Brain Evolution

INTRO
Neuroplasticity and Implications for Natural SelectionEileen DiFrancesco, M.D.

Advances in the Neurosciences force us to review Darwin’s concept of Natural Selection from a new perspective. Recent developments in our understanding of the brain include the relatively new concept of Neuroplasticity. The brain has a plasticity, meaning that enduring physical changes in brain structure are induced by learning. We call this Neuroplasticity and and it involves formation of new neurons, the basic units of brain matter, in addition to the formation of new functional circuits. The way an organism interacts with others and the environment results in changes in the brain. This is a dramatic new finding with far reaching implications. Thoughts, experiences and actions can cause neurons, their connections and entire circuits to form.

Evolution, defined as descent with modification and diversification is not debatable; it is a scientific fact. All organisms are the end products of a long natural process of change though which each species is descended from other different ones.

Natural Selection refers to Darwin’s ideas about the forces that drive evolutionary change and it forms part of the theory of Evolution. Natural Selection suggests that the sole force driving evolution is competition for food, space and mates, i.e. survival. The theory of natural selection proposes that all variations that exist amongst organisms are generated randomly; and organisms compete to increase the representation of their own genes in next generations. Any cooperation that exists amongst organisms is an incidental result of individuals seeking their own advantage.Evolution according to Darwin has no direction. It does not inevitably lead to higher things; organisms just become better adapted to their environment. Darwin described a process that relies on chance mutations and natural selection to account for the adaptive complexity of the biological world. Individuals with successful traits are more fit than their competitors; thus they reproduce and pass on their genes to offspring at a higher rate. Over time the successful traits spread to all members of the species. Natural selection coupled with inheritance of small trait differences is the agent of adaptation. It is a statistical filtering process; individuals with particular characteristics are more likely to survive and produce more offspring than others. A fundamental tenet of Darwinian evolution is that natural selection favors characteristics that enhance the fitness of individuals. It does not necessarily benefit the survival or enhance the well-being of the species. Fitness, in Darwinian evolution means the number of offspring that an individual leaves behind. Therefore individuals who die without reproducing have zero fitness. The causal association of a feature or trait with fitness operationally means that the value of a trait is directly responsible for whether an individual lives or dies, or why some individual leave behind more offspring than others. . The production of the most offspring becomes the sole mechanism for evaluation of success. Clearly Natural Selection does occur, however; many modern evolutionary biologists propose that it does not necessarily operate for the role Darwin assigned it.Developments in our understanding of the human brain suggest that natural selection may not be the only force behind evolution. Our understanding of the evolutionary layering of the human brain shows that more highly evolved brains are correlated with more cooperative behaviors. Cooperation rather than competition opposes the idea that natural selection is the sole force driving evolution. The increased complexity of behavioral patterns that emerged from reptiles to mammals to humans mirrors an enormous outgrowth of brain.

Evolutionary layering of the human brain demonstrates that it has a primitive inner core functionally analogous in many ways to an entire reptilian brain. This area of the brain serves the function of arousal and autonomic function such as regulation of blood pressure, body temperature and respiratory rate. The innermost reptilian-like layer of the human brain is surrounded by a middle layer comparable in function to the early mammalian brain. The early mammalian brain correlated with the capacity for communal activities, primitive emotion and personality. Behaviors such as separation cry, a primal vocalization, emerged along with communal bonding and territorial behavior. Early mammalian rearing of the young became more interactive than in reptilian species and is correlated with the evolution of the brain. The expanded forebrain in mammals is critically related to parental care and serves as a mechanism for extra-genetic transmission of information from one generation to the next. This transmission results from close contact with parents during infancy, which provides the young with an opportunity to observe and learn from parental behavior. The capacity to store these memories is also related to the expansion of the forebrain.

In late mammals through human primates an outer neocortical layer developed. The increased complexity of behavioral patterns that emerged in primates is correlated with outgrowth of the neocortex. The new areas of brain that evolved in the primate brain were correlated with dramatic increases in cooperative care of others. The uniquely different feature that differentiates humans from other primates is our ability to participate cooperatively in a large variety of networks from nuclear families, to neighborhoods to countries. As stated earlier in this paper , more recent developments in our understanding of the brain include the concept of Neuroplasticity. The brain has a plasticity, means that enduring physical changes in brain structure are induced by learning. The way an organism interacts with others and the environment results in changes in the brain. Thoughts, experiences and actions can cause neurons, their connections and entire circuits to form.When we consider our understanding of the evolutionary layering of the human brain and the fact that brain demonstrates plasticity ; there are implications for Natural Selection. The fact that more highly evolved species are more cooperative and caring for its members than less highly evolved species argues against the theory of natural selection, which argues for incessant competition and struggle of individual self interest as the sole force driving evolution.

In addition, the fact that brain variations are created by the manner in which individuals choose to interact with each other and their environments suggests that the species that evolve the furthest cooperate the most. Brain differences between reptiles, mammals and primates correlate with differences in functional capacity. Early mammalian rearing of the young became more interactive than in reptilian species and is correlated with a layer of brain outgrowth that surrounds an inner core which is analogous to the reptilian brain. The primate brain developed an outgrowth of neocortex that surrounds an inner core analogous to the mammalian brain. Behavioral complexities associated with outgrowth of the human primate brain include Altruism. Why would behavior involving self sacrifice for the benefit of others evolve if the force driving evolution is competition to increase the representation of one’s own genes at the expense of others? According to natural selection; individual advantage is the only criteria for success. Why do more highly evolved brains correlate with more interactive, cooperative and altruistic beings? Does the fact that behavior induces changes in the physical brain suggest that the choice to be cooperative with others wins over being competitive for self advantage? Does cooperation correlate with a more highly evolved brain and does this contribute to further evolution? Advances in the Neurosciences suggest that Darwin’s concept of Natural Selection is not the sole force driving evolution. The theory of natural Selection was formulated more than 150 years before the discovery of Neuroplasticity. The discovery of Evolution was an enormous intellectual achievement . A full understanding of the forces that drive Evolution is still ahead.