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Randall
J. Randall Murphy
Interesting examples. I have no idea how long it took those features to evolve. But even if they evolved fairly quickly by evolutionary standards, do we consider all evolution equally likely regardless of complexity? I think not. Complexity is a critical factor in evolution and the more complex something is, the longer it's supposed to take to evolve. Therefore it doesn't seem to be an equitable comparison to compare a tooth, jaw or even a dinosaur sail with the complexity of the neocortex and in particular the prefrontal cortex of homo sapiens sapiens.
Muadib
Paranormal Adept
There's really no need to invoke gods or aliens when discussing the evolution of the brain. Irreducible complexity is an "argument from ignorance" whether it's used in creationism or alien intervention theories because even if there was a failure of current science to explain how an irreducibly complex organism did or could evolve, it does not automatically prove the impossibility of such an evolution. The actual science behind the evolution of the brain is much more interesting anyway. I know it's a lot to read, but it's relevant to the discussion. I'm not going to include the last section on Learning and Memory just for the sake of space but you can click on the link at the beginning of the article if you're interested in reading it, it also includes the references section.
Without Miracles
Brain Evolution and Development:
The Selection of Neurons and Synapses
Instruction versus Selection
The 10,000 or so synapses per cortical neuron are not established immediately. On the contrary, they proliferate in successive waves from birth to puberty in man. . . . One has the impression that the system becomes more and more ordered as it receives "instructions" from the environment. If the theory proposed here is correct, spontaneous or evoked activity is effective only if neurons and their connections already exist before interaction with the outside world takes place. Epigenetic selection acts on preformed synaptic substrates. To learn is to stabilize preestablished synaptic combinations, and to eliminate the surplus.
--Jean-Pierre Changeux[1]
The most complex object yet discovered anywhere in the universe is the organ that fills the space between our ears. Although weighing only about 1300 to 1500 grams (three to four pounds), the human brain contains over 11 billion specialized nerve cells, or neurons, capable of receiving, processing, and relaying the electrochemical pulses on which all our sensations, actions, thoughts, and emotions depend.[2] But it is not the sheer number of neurons alone that is most striking about the brain, but how they are organized and interconnected. And to understand how neurons communicate with each other we first must consider their typical structure.
Although there are many different types of neurons, almost all of them share certain common features as portrayed in figure 5.1. The cell body, or soma, contains the nucleus of the neuron, which in turn houses a complete set of the organism's genes. The nucleus is surrounded by cytoplasm, the chemical "soup" of the cell that contains the organelles essential to the neuron's functioning and metabolism. In these respects, neurons are similar to other cells throughout the body, except for the fact that unlike most other cells they rarely divide to reproduce new neurons.
The ways in which neurons are specialized to carry out their communicative function is made evident by closer examination of the appendages they sport, that is, their dendrites and axons. The dendrites can be likened to a bushy antenna system that receives signals from other neurons. When a dendrite is stimulated in a certain way, the neuron to which it is attached suddenly changes its electrical polarity and may fire, sending a signal out along its single axon where it may be picked up by the dendrites of other neurons.[3] Considering the small size of the neuron's body, the length of an axon can be considerable, up to several meters in the neck of the giraffe. Thus the firing of one neuron can influence the firing of another one a considerable distance away.
For one neuron to influence another, the two must be connected, and this is accomplished by junctions called synapses (figure 5.2). These synaptic junctions usually connect the axon of one neuron with the dendrites of another, a typical neuron in the cortex of the human brain having about 10,000 synapses. The synapses therefore constitute an exceedingly complex wiring system that surpasses by many orders of magnitude the complexity of even the most advanced supercomputers. It is this organization of connections both within the skull and to more distant sense organs and muscles that gives the brain its amazing abilities. Indeed, it is widely believed today by neuroscientists, psychologists, and even philosophers that all of the knowledge the human brain contains--from being able to walk to the ability to perform abstract scientific and mathematical reasoning--is a function of the connections existing among the neurons.
How this unfathomably complex organization allows us to perceive, behave, think, feel, and control our environment presents us with what may be the most striking puzzle of fit we have yet encountered. The puzzle actually has three aspects. First, we must consider how over millions of years the primitive nervous system of our early ancestors evolved into an organ that has made it possible for the human species to become the most adaptable and powerful organism on the planet--living, thriving, and modifying the environment (both intentionally and unintentionally) from the tropics to the polar regions, and perhaps soon in outer space and on other planets.[4] Second, we must understand how it is possible for the intricate structure of the brain to develop from a single fertilized egg cell. Finally, we must try to comprehend how the mature brain is able to continue to modify its own structure so that it can acquire new skills and information to continue surviving and reproducing in an unpredictable, ever-changing world. In this chapter we will consider the research and theories that are beginning to provide answers to these questions. Indeed, the 1990s has been referred to as "the decade of the brain," as scholars and scientists in fields from philosophy to molecular neurobiology focus their energies on understanding humankind's ultimate inner frontier.
Continued...
Without Miracles
Brain Evolution and Development:
The Selection of Neurons and Synapses
Instruction versus Selection
The 10,000 or so synapses per cortical neuron are not established immediately. On the contrary, they proliferate in successive waves from birth to puberty in man. . . . One has the impression that the system becomes more and more ordered as it receives "instructions" from the environment. If the theory proposed here is correct, spontaneous or evoked activity is effective only if neurons and their connections already exist before interaction with the outside world takes place. Epigenetic selection acts on preformed synaptic substrates. To learn is to stabilize preestablished synaptic combinations, and to eliminate the surplus.
--Jean-Pierre Changeux[1]
The most complex object yet discovered anywhere in the universe is the organ that fills the space between our ears. Although weighing only about 1300 to 1500 grams (three to four pounds), the human brain contains over 11 billion specialized nerve cells, or neurons, capable of receiving, processing, and relaying the electrochemical pulses on which all our sensations, actions, thoughts, and emotions depend.[2] But it is not the sheer number of neurons alone that is most striking about the brain, but how they are organized and interconnected. And to understand how neurons communicate with each other we first must consider their typical structure.
Although there are many different types of neurons, almost all of them share certain common features as portrayed in figure 5.1. The cell body, or soma, contains the nucleus of the neuron, which in turn houses a complete set of the organism's genes. The nucleus is surrounded by cytoplasm, the chemical "soup" of the cell that contains the organelles essential to the neuron's functioning and metabolism. In these respects, neurons are similar to other cells throughout the body, except for the fact that unlike most other cells they rarely divide to reproduce new neurons.
The ways in which neurons are specialized to carry out their communicative function is made evident by closer examination of the appendages they sport, that is, their dendrites and axons. The dendrites can be likened to a bushy antenna system that receives signals from other neurons. When a dendrite is stimulated in a certain way, the neuron to which it is attached suddenly changes its electrical polarity and may fire, sending a signal out along its single axon where it may be picked up by the dendrites of other neurons.[3] Considering the small size of the neuron's body, the length of an axon can be considerable, up to several meters in the neck of the giraffe. Thus the firing of one neuron can influence the firing of another one a considerable distance away.
For one neuron to influence another, the two must be connected, and this is accomplished by junctions called synapses (figure 5.2). These synaptic junctions usually connect the axon of one neuron with the dendrites of another, a typical neuron in the cortex of the human brain having about 10,000 synapses. The synapses therefore constitute an exceedingly complex wiring system that surpasses by many orders of magnitude the complexity of even the most advanced supercomputers. It is this organization of connections both within the skull and to more distant sense organs and muscles that gives the brain its amazing abilities. Indeed, it is widely believed today by neuroscientists, psychologists, and even philosophers that all of the knowledge the human brain contains--from being able to walk to the ability to perform abstract scientific and mathematical reasoning--is a function of the connections existing among the neurons.
How this unfathomably complex organization allows us to perceive, behave, think, feel, and control our environment presents us with what may be the most striking puzzle of fit we have yet encountered. The puzzle actually has three aspects. First, we must consider how over millions of years the primitive nervous system of our early ancestors evolved into an organ that has made it possible for the human species to become the most adaptable and powerful organism on the planet--living, thriving, and modifying the environment (both intentionally and unintentionally) from the tropics to the polar regions, and perhaps soon in outer space and on other planets.[4] Second, we must understand how it is possible for the intricate structure of the brain to develop from a single fertilized egg cell. Finally, we must try to comprehend how the mature brain is able to continue to modify its own structure so that it can acquire new skills and information to continue surviving and reproducing in an unpredictable, ever-changing world. In this chapter we will consider the research and theories that are beginning to provide answers to these questions. Indeed, the 1990s has been referred to as "the decade of the brain," as scholars and scientists in fields from philosophy to molecular neurobiology focus their energies on understanding humankind's ultimate inner frontier.
Continued...
Muadib
Paranormal Adept
Continued...
The Evolution of the Brain
Neurons are quite distinct from other body cells in ways that make them suited to their specialized role of signal processing and communication, but it is not too difficult to see how they could have evolved from less specialized cells. All living cells are surrounded by a cell membrane that separates the special chemical composition of its interior from that of the external world. This difference in chemical composition results in a small electrical potential between the inside and outside of the cell, in much the same way that a voltage exists between the two sides of a battery. When a part of a cell's membrane is disturbed in a certain way, it loses its electrical potential, becoming depolarized at the site of the disturbance. This sudden change in electrical potential can itself be a disturbance, causing additional depolarizations along the membrane. In most cells, such depolarization would not spread far, certainly not to neighboring cells. But a few changes in the shape and arrangement of cells (in just the way that neurons are fashioned) permits depolarization to propagate quickly from one neuron to the next, and allows it to travel quickly as an electrochemical signal from one end of an animal to the other.
An example of a simple nervous system is provided by the jellyfish (or Medusa). The jellyfish's nervous system forms an undifferentiated network and serves primarily to coordinate the animal's swimming motions. Since the jellyfish's skirt must open and contract in a coordinated manner for the animal to move through the water, its nervous system serves as a simple communications network making it possible for all parts of the skirt to open repeatedly and then contract at the same time.
Worms are the simplest organisms to have a central nervous system, which includes a distinct brain that is connected to groups of neurons organized as nerve cords running along the length of its body. This more complicated nervous system allows worms to exhibit more complex forms of behavior. An anterior brain connected to a nerve cord is the basic design for all organisms with central nervous systems, from the earthworm on the hook to the human on the other end of the fishing rod. But although we can discern a separate brain in worms, it is not the case that the brain is the sole "commander" of the animal that the rest of the nervous system and body obeys. Indeed, even with its brain removed, worms are able to perform many types of behaviors, including locomotion, mating, burrowing, feeding, and even maze learning.[5]
As we move to insects we find increased complexity in all aspects of the brain and nervous system. So-called giant fiber systems (also found to some extent in worms and jellyfish) that allow rapid conduction of nerve impulses connect parts of the brain to specific muscles in legs or wings. Such connections permit the cockroach to dart away as soon as it senses the moving air preceding a quickly descending human foot. The brain itself is typically divided into three specialized segments, the protocerebrum, the deutocerebrum, and the tritocerebrum. In addition, insects possess a greater variety of sensory receptors than any other group of organisms, including vertebrates, that are sensitive to the odors, sounds, light patterns, texture, pressure, humidity, temperature, and chemical composition of their surroundings. The concentration of these sensory organs on the insect's head provides for rapid communication with the tiny yet capable brain located within.
Although minuscule by human standards, the range of abilities made possible by insect brains is impressive. These creatures show a remarkable variety of behaviors for locomotion, obtaining food, mating, and aiding the survival of their offspring. They can crawl, hop, swim, fly, burrow, and even walk on water. The female wasp hunts down a caterpillar, paralyzes it with her venom, and then lays its egg on the motionless prey so that her offspring will have a fresh and wholesome meal immediately after hatching. Leafcutter ants harvest leaves and bring them into their nest where they use them to cultivate indoor gardens of edible fungus. Honeybees live in social communities where there is a strict division of labor, and where foodgathering worker bees perform a special dance to communicate the location and richness of food sources to their hivemates. It is the evolution of their brains, together with the complementary evolution of their other body parts, that make insects the most abundant multicellular organisms on our planet.
The brain becomes both much larger and still more complex as we move to vertebrates such as fish, amphibians, and reptiles. The spinal cord, now protected within the vertebrae of the backbone, has become primarily a servant of the brain, a busy two-way highway of communication with fibers segregated into descending motor pathways and ascending sensory ones. The brain itself is now composed of a series of swellings of the anterior end of the spinal cord (the brain stem), the three major ones making up the three major parts of the vertebrate brain: the hindbrain, midbrain, and forebrain. From the hindbrain sprouts a distinctive structure, the "cerebellum" (Latin for "little brain").
Among mammals, the brain keeps its three major components, but with two new structures. The neocerebellum ("new cerebellum") is added to the cerebellum, looking much like a fungal growth at the base of the brain, and the neocortex ("new cortex") grows out of the front of the forebrain. In most mammals, these new additions are not particularly large relative to the brain stem. In primates they are much larger, and in the human they are so large that the original brain stem is almost completely hidden by this large convoluted mass of grey neural matter. In keeping with this remarkable increase of neocerebellar and neocortical tissue, humans enjoy the largest ratio of brain weight to body weight of any of earth's creatures.
It is not possible to know exactly why the human brain evolved as it did, but consideration of the structural evolution of the brain and results of comparative research on human and nonhuman brains provides some useful clues. It is now believed that during the long evolution of our brain, nervous systems changed in four principal ways. First, they became increasingly centralized in architecture, evolving from a loose network of nerve cells (as in the jellyfish) to a spinal column and complex brain with impressive swellings at the hindbrain and forebrain. This increasingly centralized structure also became increasingly hierarchical. It appears that newer additions to the human brain took over control from the previous additions and in effect became their new masters. Accordingly, the initiation of voluntary behavior as well as the ability to plan, engage in conscious thought, and use language depend on neocortical structures. Indeed, the human neocortex can actually destroy itself if it wishes, as when a severely depressed individual uses a gun to put a bullet through his or her skull.
Second, there was a trend toward encephalization, that is, a concentration of neurons and sense organs at one end of the organism. By concentrating neural and sensory equipment in one general location, transmission time from sense organs to brain was minimized. Third, the size, number, and variety of elements of the brain increased. Finally, there was an increase in plasticity, that is, the brain's ability to modify itself as a result of experience to make memory and the learning of new perceptual and motor abilities possible.
One way of understanding the evolution of the human brain is to see it as the addition of higher and higher levels of control. We will see in chapter 8 that the function of animal and human behavior can be understood as the control of perceptions, with perceptions corresponding to important aspects of the environment. For a sexually reproducing organism to survive and leave progeny, it must be able to control many different types of perceptions, that is, sensed aspects of its environment. At a minimum, it must be able to find food, avoid enemies, and mate. But as life evolved, the environment of our ancestors became more complex due to increasing numbers of competing organisms. So it would have been of considerable advantage to be able to perceive and control increasingly complex aspects of this environment. The bacterium E. coli can control its sensing of food and toxins only in a primitive way; organisms with more complex brains are able to sense and control much more complex aspects of their surroundings.
This capacity for increased environmental control is nowhere more striking than in our species. Using the advanced perceptual-behavioral capacities of our brain together with our culturally evolved knowledge of science and technology, we can visit ocean floors, scale the highest peaks, and set foot on other worlds. (The role that language is believed to have had in the evolution of the human brain will be considered separately in chapter 11.) But can the most complex human abilities and mental capacities be explained by natural selection? Our brain has certainly not changed appreciably over the last couple of hundred years, and yet we can solve mathematical, scientific, technological, and artistic problems that did not even exist a hundred years ago. So how could natural selection be responsible for the striking abilities of today's scientists, engineers, and artists?
This is actually the same problem that troubled Alfred Russel Wallace, as mentioned in chapter 3. It will be recalled that Wallace, despite being an independent codiscoverer of natural selection, could not, for example, imagine how natural selection could account for Africans' ability to sing and perform European music, since nothing in their native environment could have selected for such an ability. Consequently, for him the brain could only be a creation provided to us by God. We now know that in his embrace of this providential explanation, Wallace failed to realize that natural selection can lead to new abilities unrelated to those that were originally selected.
To use an example from technological evolution, the first personal computers were used to perform financial calculations in the form of electronic spreadsheets. However, these same machines with the proper software could also be used for word processing, telecommunications, computer games, and many other purposes, even though they were not originally designed with these functions in mind. A classic example of this phenomenon of functional shift in biological evolution is the transformation of stubby appendages for thermoregulation in insects and birds into wings for flight.[6] In the same way, selection pressure was undoubtedly exerted on early hominids to become better hunters. The ability to understand the behavior of other animals and organize hunting expeditions must have been very important in the evolution of our species. And the increasingly complex and adapted brain thus selected would have made other skills possible, such as making tools and using language, traits that in turn could become targets for continued natural selection. This transformation of biological structures and behaviors from one use to another was given the unfortunate name of preadaptation by Darwin, unfortunate since it can too easily be misunderstood to imply that somehow evolution "knows" what structures will be useful for future descendants of the current organisms.
American evolutionary paleontologist Stephen Jay Gould provided a better term for this phenomenon--exaptation. He made a major contribution to our understanding of evolution by insisting that we distinguish adaptation, the evolutionary process through which adaptedly complex structures and behaviors are progressively fine-tuned by natural selection with no marked change in the structure's or behavior's function, from exaptation, through which structures and behaviors originally selected for one function become involved in another, possibly quite unrelated, function. Exaptation makes it difficult if not impossible to understand why our brain evolved as it did. Although the brain allows us to speak, sing, dance, laugh, design computers, and solve differential equations, these and other abilities may well be accidental side effects of its evolution. As Gould and his associate Vrba cautioned:
Continued...
The Evolution of the Brain
Neurons are quite distinct from other body cells in ways that make them suited to their specialized role of signal processing and communication, but it is not too difficult to see how they could have evolved from less specialized cells. All living cells are surrounded by a cell membrane that separates the special chemical composition of its interior from that of the external world. This difference in chemical composition results in a small electrical potential between the inside and outside of the cell, in much the same way that a voltage exists between the two sides of a battery. When a part of a cell's membrane is disturbed in a certain way, it loses its electrical potential, becoming depolarized at the site of the disturbance. This sudden change in electrical potential can itself be a disturbance, causing additional depolarizations along the membrane. In most cells, such depolarization would not spread far, certainly not to neighboring cells. But a few changes in the shape and arrangement of cells (in just the way that neurons are fashioned) permits depolarization to propagate quickly from one neuron to the next, and allows it to travel quickly as an electrochemical signal from one end of an animal to the other.
An example of a simple nervous system is provided by the jellyfish (or Medusa). The jellyfish's nervous system forms an undifferentiated network and serves primarily to coordinate the animal's swimming motions. Since the jellyfish's skirt must open and contract in a coordinated manner for the animal to move through the water, its nervous system serves as a simple communications network making it possible for all parts of the skirt to open repeatedly and then contract at the same time.
Worms are the simplest organisms to have a central nervous system, which includes a distinct brain that is connected to groups of neurons organized as nerve cords running along the length of its body. This more complicated nervous system allows worms to exhibit more complex forms of behavior. An anterior brain connected to a nerve cord is the basic design for all organisms with central nervous systems, from the earthworm on the hook to the human on the other end of the fishing rod. But although we can discern a separate brain in worms, it is not the case that the brain is the sole "commander" of the animal that the rest of the nervous system and body obeys. Indeed, even with its brain removed, worms are able to perform many types of behaviors, including locomotion, mating, burrowing, feeding, and even maze learning.[5]
As we move to insects we find increased complexity in all aspects of the brain and nervous system. So-called giant fiber systems (also found to some extent in worms and jellyfish) that allow rapid conduction of nerve impulses connect parts of the brain to specific muscles in legs or wings. Such connections permit the cockroach to dart away as soon as it senses the moving air preceding a quickly descending human foot. The brain itself is typically divided into three specialized segments, the protocerebrum, the deutocerebrum, and the tritocerebrum. In addition, insects possess a greater variety of sensory receptors than any other group of organisms, including vertebrates, that are sensitive to the odors, sounds, light patterns, texture, pressure, humidity, temperature, and chemical composition of their surroundings. The concentration of these sensory organs on the insect's head provides for rapid communication with the tiny yet capable brain located within.
Although minuscule by human standards, the range of abilities made possible by insect brains is impressive. These creatures show a remarkable variety of behaviors for locomotion, obtaining food, mating, and aiding the survival of their offspring. They can crawl, hop, swim, fly, burrow, and even walk on water. The female wasp hunts down a caterpillar, paralyzes it with her venom, and then lays its egg on the motionless prey so that her offspring will have a fresh and wholesome meal immediately after hatching. Leafcutter ants harvest leaves and bring them into their nest where they use them to cultivate indoor gardens of edible fungus. Honeybees live in social communities where there is a strict division of labor, and where foodgathering worker bees perform a special dance to communicate the location and richness of food sources to their hivemates. It is the evolution of their brains, together with the complementary evolution of their other body parts, that make insects the most abundant multicellular organisms on our planet.
The brain becomes both much larger and still more complex as we move to vertebrates such as fish, amphibians, and reptiles. The spinal cord, now protected within the vertebrae of the backbone, has become primarily a servant of the brain, a busy two-way highway of communication with fibers segregated into descending motor pathways and ascending sensory ones. The brain itself is now composed of a series of swellings of the anterior end of the spinal cord (the brain stem), the three major ones making up the three major parts of the vertebrate brain: the hindbrain, midbrain, and forebrain. From the hindbrain sprouts a distinctive structure, the "cerebellum" (Latin for "little brain").
Among mammals, the brain keeps its three major components, but with two new structures. The neocerebellum ("new cerebellum") is added to the cerebellum, looking much like a fungal growth at the base of the brain, and the neocortex ("new cortex") grows out of the front of the forebrain. In most mammals, these new additions are not particularly large relative to the brain stem. In primates they are much larger, and in the human they are so large that the original brain stem is almost completely hidden by this large convoluted mass of grey neural matter. In keeping with this remarkable increase of neocerebellar and neocortical tissue, humans enjoy the largest ratio of brain weight to body weight of any of earth's creatures.
It is not possible to know exactly why the human brain evolved as it did, but consideration of the structural evolution of the brain and results of comparative research on human and nonhuman brains provides some useful clues. It is now believed that during the long evolution of our brain, nervous systems changed in four principal ways. First, they became increasingly centralized in architecture, evolving from a loose network of nerve cells (as in the jellyfish) to a spinal column and complex brain with impressive swellings at the hindbrain and forebrain. This increasingly centralized structure also became increasingly hierarchical. It appears that newer additions to the human brain took over control from the previous additions and in effect became their new masters. Accordingly, the initiation of voluntary behavior as well as the ability to plan, engage in conscious thought, and use language depend on neocortical structures. Indeed, the human neocortex can actually destroy itself if it wishes, as when a severely depressed individual uses a gun to put a bullet through his or her skull.
Second, there was a trend toward encephalization, that is, a concentration of neurons and sense organs at one end of the organism. By concentrating neural and sensory equipment in one general location, transmission time from sense organs to brain was minimized. Third, the size, number, and variety of elements of the brain increased. Finally, there was an increase in plasticity, that is, the brain's ability to modify itself as a result of experience to make memory and the learning of new perceptual and motor abilities possible.
One way of understanding the evolution of the human brain is to see it as the addition of higher and higher levels of control. We will see in chapter 8 that the function of animal and human behavior can be understood as the control of perceptions, with perceptions corresponding to important aspects of the environment. For a sexually reproducing organism to survive and leave progeny, it must be able to control many different types of perceptions, that is, sensed aspects of its environment. At a minimum, it must be able to find food, avoid enemies, and mate. But as life evolved, the environment of our ancestors became more complex due to increasing numbers of competing organisms. So it would have been of considerable advantage to be able to perceive and control increasingly complex aspects of this environment. The bacterium E. coli can control its sensing of food and toxins only in a primitive way; organisms with more complex brains are able to sense and control much more complex aspects of their surroundings.
This capacity for increased environmental control is nowhere more striking than in our species. Using the advanced perceptual-behavioral capacities of our brain together with our culturally evolved knowledge of science and technology, we can visit ocean floors, scale the highest peaks, and set foot on other worlds. (The role that language is believed to have had in the evolution of the human brain will be considered separately in chapter 11.) But can the most complex human abilities and mental capacities be explained by natural selection? Our brain has certainly not changed appreciably over the last couple of hundred years, and yet we can solve mathematical, scientific, technological, and artistic problems that did not even exist a hundred years ago. So how could natural selection be responsible for the striking abilities of today's scientists, engineers, and artists?
This is actually the same problem that troubled Alfred Russel Wallace, as mentioned in chapter 3. It will be recalled that Wallace, despite being an independent codiscoverer of natural selection, could not, for example, imagine how natural selection could account for Africans' ability to sing and perform European music, since nothing in their native environment could have selected for such an ability. Consequently, for him the brain could only be a creation provided to us by God. We now know that in his embrace of this providential explanation, Wallace failed to realize that natural selection can lead to new abilities unrelated to those that were originally selected.
To use an example from technological evolution, the first personal computers were used to perform financial calculations in the form of electronic spreadsheets. However, these same machines with the proper software could also be used for word processing, telecommunications, computer games, and many other purposes, even though they were not originally designed with these functions in mind. A classic example of this phenomenon of functional shift in biological evolution is the transformation of stubby appendages for thermoregulation in insects and birds into wings for flight.[6] In the same way, selection pressure was undoubtedly exerted on early hominids to become better hunters. The ability to understand the behavior of other animals and organize hunting expeditions must have been very important in the evolution of our species. And the increasingly complex and adapted brain thus selected would have made other skills possible, such as making tools and using language, traits that in turn could become targets for continued natural selection. This transformation of biological structures and behaviors from one use to another was given the unfortunate name of preadaptation by Darwin, unfortunate since it can too easily be misunderstood to imply that somehow evolution "knows" what structures will be useful for future descendants of the current organisms.
American evolutionary paleontologist Stephen Jay Gould provided a better term for this phenomenon--exaptation. He made a major contribution to our understanding of evolution by insisting that we distinguish adaptation, the evolutionary process through which adaptedly complex structures and behaviors are progressively fine-tuned by natural selection with no marked change in the structure's or behavior's function, from exaptation, through which structures and behaviors originally selected for one function become involved in another, possibly quite unrelated, function. Exaptation makes it difficult if not impossible to understand why our brain evolved as it did. Although the brain allows us to speak, sing, dance, laugh, design computers, and solve differential equations, these and other abilities may well be accidental side effects of its evolution. As Gould and his associate Vrba cautioned:
. . . current utility carries no automatic implication about historical origin. Most of what the brain now does to enhance our survival lies in the domain of exaptation--and does not allow us to make hypotheses about the selective paths of human history. How much of the evolutionary literature on human behavior would collapse if we incorporated the principle of exaptation into the core of our evolutionary thinking?[7]
But although we may never know the actual events and specific selection pressures responsible for our brain power, we have no scientific reason to believe that evolution could not have fashioned our brain through natural selection. The fact that living organisms today have nervous systems and brains ranging from quite simple to amazingly complex is compelling evidence that our brain evolved through forgotten ancestors in progressive stages from simple to complex. And somehow, as a part of this evolutionary process, that most remarkable and mystifying of all natural phenomena came into being--human consciousness.Continued...
Muadib
Paranormal Adept
Continued...
The Development of the Brain
From this evolutionary perspective, one might be led to conclude that our brain in all its striking adapted complexity is an inherited legacy of biological evolution. That once evolved it is thereafter provided to each individual by good old natural selection, specified in all its fine detail in the genome and transmitted through the generations from parent to offspring.
This type of genetically providential thinking of course is selectionist from the viewpoint of biological evolution, but nonetheless providential at the level of the individual organism. It can be seen in the pioneering work on brain development and function of Roger Sperry for which he shared a Nobel prize in 1981. This research in the 1950s involved disturbing the normal location of nerve fibers in the developing brains of fish and rats. For example, nerve fibers that normally connect the top part of the fish's retina with the bottom part of the brain, called the optic tectum, were surgically removed and reconnected to the top part of the optic tectum. Despite this modification, the nerve grew back to its normal position in the brain. Similar experiments carried out by other researchers on rats indicated that fibers that innervate muscles also "knew" to which muscle they should be attached and made their proper connections despite surgical disturbances. This led Sperry to conclude that the connections of the nervous system are completely specified in the organism's genes. As his former student Michael Gazzaniga explains:
How then is the brain able to achieve the very specific and adapted wiring required to function in so many remarkable ways? For example, how does a motor neuron know to which particular muscle fiber it should connect? How is a sensory neuron in the visual system able to join itself to the correct cell in the visual cortex located in the occipital lobe of the brain? If this detailed neuron-to-neuron connection information is not provided by the genes, whence does it come?
The first clues to solving this puzzle go back to 1906 when it was observed that in embryonic nerve tissue, some neurons did not stain well and appeared to be degenerating and dying.[12] Since it had been assumed that in a developing embryo, nerve cells should be increasing in number and not dying off, this finding was somewhat surprising. But nerve cell death in the developing nervous system has since been observed repeatedly. The extent to which it occurs was dramatically demonstrated by Viktor Hamburger. He found that in a certain area of the spinal cord of the chicken embryo over 20,000 neurons were present, but that in the adult chicken only about 12,000, or 60%, of these cells remained.[13] Much of this neuronal death occurs during the early days of the embryo's existence. Nerve cells continue to expire thereafter, albeit at a slower pace.
A particularly striking example of neuronal elimination in development involves the death of an entire group of brain cells:
The ability of axons to connect to the appropriate regions of the brain during development has been studied in careful detail since the beginning of this century. Axons grow in the brain like the stem of a plant. At the end of the growing axon is found a growth cone which was described by Spanish neuroscientist Ramón y Cajal in 1909 as "a sort of club or battering ram, possessing an exquisite chemical sensitivity, rapid amoeboid movements, and a certain driving force that permits it to push aside, or cross, obstacles in its way . . . until it reaches its destination."[15] Although the exact mechanisms by which this is accomplished are still unknown, it appears that the growth cone is sensitive to certain chemicals along its path that are released by its target region. In this way visual system axons originating in the lateral geniculate nucleus find their way to cortical layer 4 in the occipital lobe of the brain in much the same way that a police bloodhound is able to sniff out the escaped prisoner hiding in an Illinois cornfield.
But although these growth cones lead their axons to the proper region of the brain (or muscle in the case of motor neurons), they cannot lead them to the precise target addresses. For a particular growth cone, it appears that any cell of a particular type will serve as a target. Indeed, in the newborn cat, ocular columns receive axons from both eyes, not just from one or the other, as in the adult brain. For this final and important fine-tuning to be achieved (on which stereoscopic vision depends), many of the original terminal connections of the axon must be eliminated. In the case of vision, all axonal connections from the wrong eye are eliminated, and those from the correct eye are retained. In the case of motor systems that initially have many-to-many connections between motor neurons of the spinal column and muscle fibers (that is, many motor neuron axons connected to same muscle fiber, and many muscle fibers connected to the same axon), the mature animal possesses a much more finely ordered system with each muscle fiber enervated by one and only one motor neuron. The mammalian nervous system changes from birth to maturity from a degenerate system having many redundant and diffuse connections, to a much more finely tuned system that makes both adaptedly complex behaviors and perceptions (such as stereoscopic vision) possible.
So now the question naturally arises, how does the nervous system know which connections to retain and which to eliminate? The work of David Hubel and Torsten Wiesel in the 1970s (both of whom shared a Nobel prize with Sperry in 1981) provided the first clue. They conducted their ground-breaking experiments by closing the lid of one eye of newborn cats, and found that even one week without sight altered the connections of the eyes to layer 4 of the occipital cortex. Axons carrying nervous signals from the closed eye made fewer connections with the cortex, whereas axons from the open eye made many more connections than was normal. This suggested that visual system axons compete for space in the visual cortex, with the result of the competition dependent on the amount and type of sensory stimulation carried by the axons. Subsequent research by others using drugs to block the firing of visual system neurons, as well as artificial stimulation of these neurons, showed that it is not neural activity per se that results in the selective elimination of synapses, but rather that only certain types of neural activity result in the retention of certain synapses, while all others are eventually eliminated.
Nonetheless, interactive postnatal experience of the external world is required for normal development of senses and nervous systems in mammals. Cats who have one eye sewn shut at birth lose all ability to see with this eye when it is opened several months later. The same applies to humans. Before the widespread use of antibiotics, eye infections left many newborn infants with cloudy lenses and corneas that caused functional blindness, even though their retinas and visual nervous systems were normal at the time of birth. Years later a number of these individuals underwent operations to replace their cloudy lenses and corneas with clear ones, but it was too late. Contrary to initial expectations, none of these people was able to see after the transplant.[18]It was simply not known at the time that early visual experience was essential to the normal maturation of the brain's visual circuitry. Similarly, some children are born with a wandering eye that does not fixate the same part of the visual field as the normal eye, and other children have one eye that is seriously nearsighted or farsighted; in both cases, the retina of the abnormal eye must be provided with clear visual stimulation, usually by age four years, or it will become functionally blind since its connections to the brain's vision centers will be eliminated in favor of the normal eye.
We thus see that the normal development of the brain depends on a critical interaction between genetic inheritance and environmental experience. The genome provides the general structure of the central nervous system, and nervous system activity and sensory stimulation provide the means by which the system is fine-tuned and made operational. But this fine-tuning does not depend on adding new components and connections in the way that a radio is assembled in a factory, but rather it is achieved by eliminating much of what was originally present. It is as if the radio arrived on the assembly line with twice as many electrical components and connections as necessary to work. If such an overconnected radio were plugged in and turned on, nothing but silence, static, or a hum would be heard from its speaker. However, careful removal of unnecessary components and judicious snipping of redundant wires would leave just those components and connections that result in a functioning radio. This snipping is analogous to the elimination of synapses in the human brain as part of its normal development.
The process by which brain connections change over time as maturing animals interact with their environments has been studied in detail by psychologist William Greenough of the University of Illinois at Urbana-Champaign. Using sophisticated techniques for determining the numbers and densities of neurons and synapses in specific regions of the rat's brain, he and his associates found that during the first months of the rat's life a rapid spurt in the growth of synapses occurs regardless of the amount or type of sensory experience.[19] This period of synaptic "blooming" is followed by a sharp decline in the number of synapses. That is, an elimination or "pruning" of synapses then takes place based on the activity and sensory stimulation of the brain, and ultimately results in the configuration of connections characteristic of the mature rat's brain. Greenough refers to this initial blooming and pruning of synapses as "experience-expectant" learning, since the initial synaptic overproduction appears to be relatively independent of the animal's experiences. It is as though the brain is expecting important things to be happening during the first weeks and months of life, and is prepared for these experiences with an overabundance of synapses, only a fraction of which, however, will be selectively retained.
The work of Greenough and his associates is limited to rats and monkeys, but their findings have much in common with those of Peter Huttenlocher of the University of Chicago who counted the synapses in specific regions of the brains of humans who died at various ages. Huttenlocher found that:
The Development of the Brain
From this evolutionary perspective, one might be led to conclude that our brain in all its striking adapted complexity is an inherited legacy of biological evolution. That once evolved it is thereafter provided to each individual by good old natural selection, specified in all its fine detail in the genome and transmitted through the generations from parent to offspring.
This type of genetically providential thinking of course is selectionist from the viewpoint of biological evolution, but nonetheless providential at the level of the individual organism. It can be seen in the pioneering work on brain development and function of Roger Sperry for which he shared a Nobel prize in 1981. This research in the 1950s involved disturbing the normal location of nerve fibers in the developing brains of fish and rats. For example, nerve fibers that normally connect the top part of the fish's retina with the bottom part of the brain, called the optic tectum, were surgically removed and reconnected to the top part of the optic tectum. Despite this modification, the nerve grew back to its normal position in the brain. Similar experiments carried out by other researchers on rats indicated that fibers that innervate muscles also "knew" to which muscle they should be attached and made their proper connections despite surgical disturbances. This led Sperry to conclude that the connections of the nervous system are completely specified in the organism's genes. As his former student Michael Gazzaniga explains:
In the original Sperry view of the nervous system, brain and body developed under tight genetic control. The specificity was accomplished by the genes' setting up chemical gradients, which allowed for the point-to-point connections of the nervous system.[8]
But there is a vexing problem with the notion that the genome provides complete information for the construction of the nervous system of humans and other mammals. It is estimated that just the human neocortex alone has about 1015 (one followed by 15 zeros, or one thousand million million) synapses.[9] Since the human genome has only about 3.5 billion (3.5 x 109) bits of information (nucleotide base pairs), with 30% to 70% of these appearing silent,[10] some neural and molecular scientists have concluded that our genes simply do not have enough storage capacity to specify all of these connections, in addition to including information on the location and type of each neuron plus similar information for the rest of the body. The problem is not unlike trying to save a document made up of 100 million characters on a computer disk that can hold only 1.4 million characters. As Changeux noted:Once a nerve cell has become differentiated it does not divide anymore. A single nucleus, with the same DNA, must serve an entire lifetime for the formation and maintenance of tens of thousands of synapses. It seems difficult to imagine a differential distribution of genetic material from a single nucleus to each of these tens of thousands of synapses unless we conjure up a mysterious "demon" who selectively channels this material to each synapse according to a preestablished code! The differential expression of genes cannot alone explain the extreme diversity and specificity of connections between neurons. [11]
Additional understanding of the relation between the genome and the nervous system can be gained by considering Daphnia magna. Commonly referred to as the water flea or daphnid, this small fresh-water crustacean is familiar to many aquarium owners since it is relished by tropical fish. But what makes the daphnid interesting for our current purposes is that when the female is isolated from males, she can most conveniently reproduce by the asexual process of parthenogenesis, giving birth to genetically identical clones. In addition, the daphnid has a relatively simple nervous system that facilitates its study. If its genome completely controlled the development of its nervous system, it should be the case that genetically identical daphnids should have structurally identical nervous systems. However, examination of daphnid eyes using the electron microscope reveals that although genetically identical clones all have the same number of neurons, considerable variation exists in the exact number of synapses and in the configurations of connections leading to and away from the cell body of each neuron, that is, the dendritic and axonal branches. As we move to more complex organisms, the variability of their nervous systems increases. This provides clear evidence that the structure and wiring of the nervous system are not the result of following a detailed construction program provided by the genes.How then is the brain able to achieve the very specific and adapted wiring required to function in so many remarkable ways? For example, how does a motor neuron know to which particular muscle fiber it should connect? How is a sensory neuron in the visual system able to join itself to the correct cell in the visual cortex located in the occipital lobe of the brain? If this detailed neuron-to-neuron connection information is not provided by the genes, whence does it come?
The first clues to solving this puzzle go back to 1906 when it was observed that in embryonic nerve tissue, some neurons did not stain well and appeared to be degenerating and dying.[12] Since it had been assumed that in a developing embryo, nerve cells should be increasing in number and not dying off, this finding was somewhat surprising. But nerve cell death in the developing nervous system has since been observed repeatedly. The extent to which it occurs was dramatically demonstrated by Viktor Hamburger. He found that in a certain area of the spinal cord of the chicken embryo over 20,000 neurons were present, but that in the adult chicken only about 12,000, or 60%, of these cells remained.[13] Much of this neuronal death occurs during the early days of the embryo's existence. Nerve cells continue to expire thereafter, albeit at a slower pace.
A particularly striking example of neuronal elimination in development involves the death of an entire group of brain cells:
Most frequently, neuron death affects only some of the neurons in a given category. However, in one case . . . a whole category of cells dies. These particular neurons of layer I, the most superficial layer of the cerebral cortex, characteristically have axons and dendrites oriented parallel to the cortical surface rather than perpendicular to it, like the pyramidal cells. These cells were first observed in the human fetus but have since been found in other mammals. Purely and simply, they disappear in the adult.Changeux (1985, p. 217).[14]
But the death of obviously useless brain cells cannot account for the specific connections that are achieved by the remaining neurons. For example, the visual cortex of cats and monkeys has what are called ocular dominance columns within a specific region known as cortical layer 4. In any one column of this brain area in the adult animal we find only axons that are connected to the right eye, while in the neighboring column are located only axons with signals originating from the left eye. So not only must the axons find their way to a specific region of the brain, which can be quite far from where their cell bodies are located, they must also find a specific address within a certain neighborhood.The ability of axons to connect to the appropriate regions of the brain during development has been studied in careful detail since the beginning of this century. Axons grow in the brain like the stem of a plant. At the end of the growing axon is found a growth cone which was described by Spanish neuroscientist Ramón y Cajal in 1909 as "a sort of club or battering ram, possessing an exquisite chemical sensitivity, rapid amoeboid movements, and a certain driving force that permits it to push aside, or cross, obstacles in its way . . . until it reaches its destination."[15] Although the exact mechanisms by which this is accomplished are still unknown, it appears that the growth cone is sensitive to certain chemicals along its path that are released by its target region. In this way visual system axons originating in the lateral geniculate nucleus find their way to cortical layer 4 in the occipital lobe of the brain in much the same way that a police bloodhound is able to sniff out the escaped prisoner hiding in an Illinois cornfield.
But although these growth cones lead their axons to the proper region of the brain (or muscle in the case of motor neurons), they cannot lead them to the precise target addresses. For a particular growth cone, it appears that any cell of a particular type will serve as a target. Indeed, in the newborn cat, ocular columns receive axons from both eyes, not just from one or the other, as in the adult brain. For this final and important fine-tuning to be achieved (on which stereoscopic vision depends), many of the original terminal connections of the axon must be eliminated. In the case of vision, all axonal connections from the wrong eye are eliminated, and those from the correct eye are retained. In the case of motor systems that initially have many-to-many connections between motor neurons of the spinal column and muscle fibers (that is, many motor neuron axons connected to same muscle fiber, and many muscle fibers connected to the same axon), the mature animal possesses a much more finely ordered system with each muscle fiber enervated by one and only one motor neuron. The mammalian nervous system changes from birth to maturity from a degenerate system having many redundant and diffuse connections, to a much more finely tuned system that makes both adaptedly complex behaviors and perceptions (such as stereoscopic vision) possible.
So now the question naturally arises, how does the nervous system know which connections to retain and which to eliminate? The work of David Hubel and Torsten Wiesel in the 1970s (both of whom shared a Nobel prize with Sperry in 1981) provided the first clue. They conducted their ground-breaking experiments by closing the lid of one eye of newborn cats, and found that even one week without sight altered the connections of the eyes to layer 4 of the occipital cortex. Axons carrying nervous signals from the closed eye made fewer connections with the cortex, whereas axons from the open eye made many more connections than was normal. This suggested that visual system axons compete for space in the visual cortex, with the result of the competition dependent on the amount and type of sensory stimulation carried by the axons. Subsequent research by others using drugs to block the firing of visual system neurons, as well as artificial stimulation of these neurons, showed that it is not neural activity per se that results in the selective elimination of synapses, but rather that only certain types of neural activity result in the retention of certain synapses, while all others are eventually eliminated.
In a sense, then, cells that fire together wire together. The timing of the action-potential activity is critical in determining which synaptic connections are strengthened and which are weakened and eliminated. Under normal circumstances, vision itself acts to correlate the activity of neighboring retinal ganglion cells, because the cells receive inputs from the same parts of the visual world.[16]
The dependence of the development of the visual system on sensory stimulation would seem to indicate that the fine-tuning of its connections would have to wait until the birth of the animal when it is delivered from the comforting warm darkness of the womb to the cold light of day. However, recent evidence suggests that this fine-tuning actually begins to take place in utero. Prenatal development appears to depend on spontaneous firing of retinal cells that do not depend on light stimulation from the external world. Similar endogenous patterns of activity may also exist in the spinal cord, and may refine the synaptic connections of motor systems as well.[17]Nonetheless, interactive postnatal experience of the external world is required for normal development of senses and nervous systems in mammals. Cats who have one eye sewn shut at birth lose all ability to see with this eye when it is opened several months later. The same applies to humans. Before the widespread use of antibiotics, eye infections left many newborn infants with cloudy lenses and corneas that caused functional blindness, even though their retinas and visual nervous systems were normal at the time of birth. Years later a number of these individuals underwent operations to replace their cloudy lenses and corneas with clear ones, but it was too late. Contrary to initial expectations, none of these people was able to see after the transplant.[18]It was simply not known at the time that early visual experience was essential to the normal maturation of the brain's visual circuitry. Similarly, some children are born with a wandering eye that does not fixate the same part of the visual field as the normal eye, and other children have one eye that is seriously nearsighted or farsighted; in both cases, the retina of the abnormal eye must be provided with clear visual stimulation, usually by age four years, or it will become functionally blind since its connections to the brain's vision centers will be eliminated in favor of the normal eye.
We thus see that the normal development of the brain depends on a critical interaction between genetic inheritance and environmental experience. The genome provides the general structure of the central nervous system, and nervous system activity and sensory stimulation provide the means by which the system is fine-tuned and made operational. But this fine-tuning does not depend on adding new components and connections in the way that a radio is assembled in a factory, but rather it is achieved by eliminating much of what was originally present. It is as if the radio arrived on the assembly line with twice as many electrical components and connections as necessary to work. If such an overconnected radio were plugged in and turned on, nothing but silence, static, or a hum would be heard from its speaker. However, careful removal of unnecessary components and judicious snipping of redundant wires would leave just those components and connections that result in a functioning radio. This snipping is analogous to the elimination of synapses in the human brain as part of its normal development.
The process by which brain connections change over time as maturing animals interact with their environments has been studied in detail by psychologist William Greenough of the University of Illinois at Urbana-Champaign. Using sophisticated techniques for determining the numbers and densities of neurons and synapses in specific regions of the rat's brain, he and his associates found that during the first months of the rat's life a rapid spurt in the growth of synapses occurs regardless of the amount or type of sensory experience.[19] This period of synaptic "blooming" is followed by a sharp decline in the number of synapses. That is, an elimination or "pruning" of synapses then takes place based on the activity and sensory stimulation of the brain, and ultimately results in the configuration of connections characteristic of the mature rat's brain. Greenough refers to this initial blooming and pruning of synapses as "experience-expectant" learning, since the initial synaptic overproduction appears to be relatively independent of the animal's experiences. It is as though the brain is expecting important things to be happening during the first weeks and months of life, and is prepared for these experiences with an overabundance of synapses, only a fraction of which, however, will be selectively retained.
The work of Greenough and his associates is limited to rats and monkeys, but their findings have much in common with those of Peter Huttenlocher of the University of Chicago who counted the synapses in specific regions of the brains of humans who died at various ages. Huttenlocher found that:
The increase in synaptic density plus expansion of total cortical volume leave no doubt that the postnatal period is one of very rapid synaptogenesis in human frontal cortex. By age 2 years, synaptic density is at its maximum, at about the same time when other components of cerebral cortex also cease growing and when total brain weight approaches that of the adult. Synaptic density declines subsequently, reaching by adolescence an adult value that is only about 60% of the maximum.[20]
Muadib
Paranormal Adept
Continued...
This wealth of synapses is thought to be responsible for the striking plasticity of the immature brain that permits the learning of skills that can be learned only with much greater difficulty or not at all by the already pruned adult brain. We already saw how immature animals and children are unable to develop normal vision if they are not exposed to a sharply focused visual world during this period of brain development. It has also been repeatedly observed that although many adults initially may make quite rapid progress in learning a foreign language, young children appear to have an important advantage over adults in being able to master the sounds of languages. Canadian child language researchers Janet Werker and Richard Tees observed that children younger than one year appear able to distinguish between the speech sounds used by any human language. By age 12 months, however, they begin to lose the ability to discriminate between sound contrasts that are not used in the language they hear every day. So whereas all normal infants can distinguish between the two related but distinct sounds represented by the letter t in Hindi, those who hear only English quickly lose this ability, and Hindi-speaking children retain it.[21] The work of Werker and Tees therefore provides important human behavioral evidence that is consistent with the view that normal brain development involves the loss of synaptic connections, which results in the loss of certain skills as the brain approaches its adult form.
A sensitive period for the acquisition of a first language was demonstrated by the plight of Genie, an American girl who was brutally isolated from all normal human interaction until she was found at age 13 years, and who never subsequently developed normal language abilities.[22] There is striking evidence that the immature, overconnected brain is also better suited than a mature one to acquiring second languages and sign languages.[23]
Taken together, these findings paint a picture of the developing brain that contrasts sharply from the genetic providentialism favored by Sperry. Instead of the brain unfolding according to a genetically specified blueprint, we see instead a process of selection by which overly abundant neuronal connections are eliminated through a weeding-out process, leaving only those connections that permit the animal to interact successfully with its environment.
This wealth of synapses is thought to be responsible for the striking plasticity of the immature brain that permits the learning of skills that can be learned only with much greater difficulty or not at all by the already pruned adult brain. We already saw how immature animals and children are unable to develop normal vision if they are not exposed to a sharply focused visual world during this period of brain development. It has also been repeatedly observed that although many adults initially may make quite rapid progress in learning a foreign language, young children appear to have an important advantage over adults in being able to master the sounds of languages. Canadian child language researchers Janet Werker and Richard Tees observed that children younger than one year appear able to distinguish between the speech sounds used by any human language. By age 12 months, however, they begin to lose the ability to discriminate between sound contrasts that are not used in the language they hear every day. So whereas all normal infants can distinguish between the two related but distinct sounds represented by the letter t in Hindi, those who hear only English quickly lose this ability, and Hindi-speaking children retain it.[21] The work of Werker and Tees therefore provides important human behavioral evidence that is consistent with the view that normal brain development involves the loss of synaptic connections, which results in the loss of certain skills as the brain approaches its adult form.
A sensitive period for the acquisition of a first language was demonstrated by the plight of Genie, an American girl who was brutally isolated from all normal human interaction until she was found at age 13 years, and who never subsequently developed normal language abilities.[22] There is striking evidence that the immature, overconnected brain is also better suited than a mature one to acquiring second languages and sign languages.[23]
Taken together, these findings paint a picture of the developing brain that contrasts sharply from the genetic providentialism favored by Sperry. Instead of the brain unfolding according to a genetically specified blueprint, we see instead a process of selection by which overly abundant neuronal connections are eliminated through a weeding-out process, leaving only those connections that permit the animal to interact successfully with its environment.
Stagger Lee
Paranormal Adept
Hey starise, yeah, big fan since late 1980's.
I prob shouldn't have used the term "disclosure" as a thread title... as I'm thinking more along the lines of some type of extraordinary event that might occur, forcing everyone to take a serious look at the reality of this subject. I saw an interesting list someone posted in this forum, of the snowball effect this would have. Obviously, it would have to be something the media takes and beats the heck out of- not just a headline in the huff post.
Ezechiel
Paranormal Adept
This is a view that is starting to make a lot more sense to me.
The moment we uncover a shortcut enabling humanity to bypass Einsteinian limitations we should rapidly discover all the other life forms in this universe that have also learned how to manipulate space/time dimensions. We'll finally be part of a sentient grid... a Matrix and finally learn why this sentient grid never interfered in earthly matters... or how it did.
In the grand scheme of things we'll simply discover that planet earth is lost among an infinity of life pods... except that we will have awakened and now have an impact on a cosmic scale. What lies beyond this nursery are probably forces that protect it. I foresee a meeting with the managers
Trajanus
Paranormal Adept
IIRC the Kaprosuchus yielding beds conformably overlie the El Rhaz in which nothing like it is known, which suggests rapid evolution. Same apparently true for Tyrannosaurus, which was already evolving by mid Maastrichtian, or soon after the Nemegtian period in which the tyrannosaurs, albeit related to T., lacked its posterior skull expansion and extraordinary jaw musculature.
.
There was a leap in complexity but it did build on the earlier advances of Homo erectus and H. ergaster over australopithecus. No doubt the case for ET intervention would be stronger if H. s. sapiens was preceeded by nothing more brainy than say, A. robustus.
Randall
J. Randall Murphy
What does that amount to in a time span of years?
The earlier advances are IMO just as odd, if not more so. Standard evolutionary theory suggests that organisms should evolve very slowly over a long time in a manner that is much more integrated. But the neocortex was essentially bolted on after the fact as an entirely different layer of the brain. What we should be seeing is an expansion of the existing neuro-architecture. Instead what we have is analogous to overlaying a next generation high density chip with significant differences in design and capacity onto an existing core. A longer tooth, stronger jaw or sharper claw are not the same as radically new jaws, claws or teeth. Then that new brain layer for some as yet unexplained reason spontaneously makes a few leaps in size and capacity resulting in extreme complexity that gave rise to higher thinking, the kind of thinking we'd never had before. On this issue, evolution suggests that natural selection is based on proven traits that increase survival and perpetuates the species. A claw, tooth or jaw makes sense, as does a better wing or cooling system. They are practical things used every day, or in the case of the dinosaur sail, used continuously and without any added effort. It seems very natural that such things should evolve ( even fairly rapidly ). But what reason would billions of connections of neuro-processing power spontaneously come into existence for? By all logic, their purpose would have been literally incomprehensible to previous generations, and therefore they would not have been of any proven value. The typical explanation is random mutation. Forgive me for being dubious about the idea that the most powerful neuro-processor known to exist just randomly mutated into existence. Followed by that we begin to find creation myths that credit some highly advanced entities with bringing about these changes. What evidence do we have that such entities may exist? Are multiple witness radar/visual reports sufficient? Are ancient myths of similar things only just myths?
Nevertheless you still make fair points. Left unattended nature does some pretty amazing things, so I certainly wouldn't bet my life savings on the theory that intervention has taken place. Also, what I find really excellent about these kinds of discussions is that friendly and rational point/counterpoint encourages participation in mainstream science, history and other fields of inquiry. All too often discussions about the mysteries in life are criticized as detracting from scientific progress, but discussions like this IMO do exactly the opposite. They make us think and encourage people who become interested and seek out the answers by investigating and using the amazing tools and advancements we've made. So for me, even though alien intervention is a really cool concept that I'd like to see proven, all the science that we can apply to making that determination is also really cool. Provided we can keep our sense of perspective and not become so invested in our beliefs that we ignore facts favoring one theory or the other, it's a win-win situation for learning.
Trajanus
Paranormal Adept
The ages of these units are poorly constrained. In the case of Tyrannosaurus, from virtually nothing to 1-2 million years.
Hominid/human evolution seems to have turned the usual course of evolution on its head. For most of evolutionary history, greater physical strength usually won out; in this case, better brains, which presumably conferred an ability to make weapons or better ones, prevailed. Even before our species beat out H. s. neanderthalensis, H. erectus seems to have done the same to A. robustus.
I think the selection pressures were pretty strong.
The latter can be attributed simply to an inability to explain things any other way. Modern sightings have more evidence.
Bingo!
Randall
J. Randall Murphy
The ability to use physical objects as tools is demonstrated by quite a few animals, even ones with fairly small brains, including birds, but that is entirely different. For example, Homo floresiensis, had a brain size of only 380 cc, a third of that of their proposed ancestor H. erectus, but used fire, hunted, and made stone tools at least as sophisticated as those of H. erectus. So what we're getting into with modern humans is a substantially different type of thinking, something never experienced before, and therefore unproven as a force in natural selection ( the key factor driving evolution ). So without the influence of natural selection, what gives an organ safely enclosed inside a case of bone and unexposed to the environmental and physical forces that gave rise to better claws, teeth, jaws, wings ( whatever ) the stimulus to evolve? One theory suggest that when we started walking upright ( like bonobos are starting to do now ), it freed our hands to do more things directly related to survival ( like carrying food and supplies with our hands and arms ). But then we're still left to suppose that the kind of abstract thinking that makes us truly human and takes place in very specialized regions of the brain just sort of ... well what exactly? We still don't know exactly why or how it happened.
Then again, maybe there really isn't any why or how, and it was just spontaneous mutation, but our brains can't accept that because we're just not wired that way. In an odd sort of way those without mutation might even see it as a kind of evolutionary freak of nature without any apparent value. How many times are we told to "work don't think". The primitive practical physical brain is still very active. We could even look at this as a kind of sci-fi analogy where some mutation gives someone some extrasensory powers or Rain Man like abilities without the downsides. At first it might seem that such people are freaks or misfits too.
Trajanus
Paranormal Adept
It's one thing to be able to use tools, another to be able to make them. I'd assume the latter required better brains. H. floresiensis is very recent and controversial.