Paleoneurology and the evolution of mind

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What is "intelligence"? What is "biologically programmed behavior"? How do these behavioral patterns relate to other aspects of the biology of the animals that possess them, and to their reproductive biology in particular? How does intelligence relate to learned behavior and more specifically, to human culture?

"Biologically programmed behavior' explains most, but not all, non-mammal vertebrate behavior. Early studies of non-mammal vertebrates characterized behavior as "instinct" -a term that suggested that such behaviors are fixed and immutable. Later studies documented both a degree of flexibility and the ability to learn new behavioral patterns by non-mammal vertebrates. Such studies have also shown that mammals, in general, have a greater repertoire of learned behaviors than earlier vertebrates. "Biologically programmed behavior" is, therefore, better understood as a range of programmed behaviors which have increased remarkably with the evolution of the mammal biological complex.

The neurological basis for learned behavior and intelligence are, in large part, due to changes in the reproductive system. Internal fertilization first occurred in the evolution of reptiles. In the evolution of placental mammals, there was not only internal fertilization, but also embryological development in utereo. Such a reproductive system provides a basis for the animal to grow into a developed state before having to face the external world. Placentation, a mother's ability to supply nutrients and oxygen to a developing embryo, is not without disadvantages; in animals such as the higher primates, the mother's blood stream and the developing embryo blood stream have a close connection with the placenta. In many placental mammals, there is a rather non-porous membrane, which separates the maternal bloodstream from the embryonic bloodstream, while allowing nutrients to pass. If there is major mutation in the embryo, which is reflected in the embryonic blood stream, the mother's bloodstream will not interact with the mutation and will not produce antibodies, which would kill the embryo. In the higher primates, this membrane is much more permeable and much more efficient in the transmission of nutrients. A disadvantage is that any major embryonic mutation, which is reflected in the embryonic bloodstream, will produce antibodies against the mutation; this normally results in spontaneous abortion or miscarriage.

Uterine development has helped mammals insure the greater success of their offspring. The mammalian survival strategy is known as the "K strategy," and it is based upon a high parental investment in specie survival. Nurturing a smaller number of offspring ensures a higher percentage of those offspring will reach reproductive maturity. A reduction in birth number is associated with birth of live young in most mammals. This strategy is different from the vertebrate "R strategy," where the parent produces a large number of eggs, which when fertilized produce a large number of young. The difference in these two survival strategies can be supported by the different attitudes toward death. In humans (and other mammals) death of young mammals is a serious trauma; in vertebrates the death of a hatchling is the rule of nature, and survival is the exception.

The stimulus -response loop characterizes much of the behavior of earlier vertebrates. A sensory input comes into the vertebrate brain, which is linked to a stereotype motor output. A famous example of "biologically programmed behavior" is the reproductive behavior of the three-spined Stickleback of the Rhine/North Sea. An external event triggers a series of biologically linked behaviors, which results in successful reproduction. As spring occurs in North Sea, there is more daylight. This stimulates the pineal gland of the female, which, in turn, signals the hypothalamus, which produces a neurotransmitting chemical to the pituitary gland. This in turn results in the secretion of pituitary hormones, which stimulates the ovaries to produce thousands of eggs. This gives the female a swollen belly and is a "sign stimulus" to the male stickleback. In response, the male does a "zigzag dance," which is referred to as a "fixed action pattern." The dance, in turn, acts as a sign stimulus to the female, who follows the male to the nest, and through an additional series of sign stimuli and fixed action patterns, moves through the nest to deposit the eggs. The male then passes over the eggs with sperm. Natural selection favors the retention of these neurological pathways in the males and females because they successfully function to produce fertilization; to put it the other way, if a female has a neurological change where she would not recognize the zigzag dance, she will not be able to reproduce. In a series of experiments, Tinbergen and his students were able to show that the swollen belly of the female stickleback is the initiating sign stimulus. Raising male stickleback in total isolation, they introduced them into the water with both living females as well as with metal outlines of females with swollen bellies. Regardless (and even when the outline of the female was grossly distorted), the males produced the zigzag dance. It was "hardwired" in their nature. Individual animals, therefore, have little direct input in changing behavioral sequences. Once the female has laid her eggs, and they have been fertilized, that represents the end of parental investment. It is not hard to see how climate or other change can rapidly end an entire species that relies on biologically programmed behavior for reproduction. The absence of daylight for a single spring in the North Sea would mean the end of stickleback reproduction.

Young mammals are born helpless and dependent, and they go through a prolonged infancy and youth of nurturing entirely dependent on adult generation. Because the parental investment of mammals is the care of very small number of offspring, the responsibility falls mainly on females. There was also an evolution of mammary glands for this postal nurturing period. During this time of helplessness, the animal has the freedom to discover the world, while being feed and protected. This reproductive system of mammals, therefore, allows the mammal cerebral cortex to incorporate and internalize the sensory patterns the animal has experienced. The animal is utilizing intelligence -the "ability to construct a perceptual model of the world inside your head" (Jerison).

The mammal brain has developed into a structure, which provided the basis for both learned behavior and intelligence. The role of the brain is to impose a model of the world on sensory data, and provide appropriate responses to it. This is not an entirely new development; it represents an evolution of the cerebral cortex as a mediator between perception and response (motor output), and the integration of input from an acute auditory sensory system.

Learned behavior and intelligence are not the same. Learned behavior is the ability of an animal to sort through a variety of possible behavioral outcomes, and pick which behavior is appropriate. When driving a car, for example, an individual has to pick when it is appropriate to turn right at a red light. Learned behavior is part of the mammal pattern, but it is differentially distributed; humans have an enormous ability for learned behavior, compared to the limited levels of other mammals. The fundamental explanation is the cerebral cortex. Choice behavior is located in the frontal lobe. Humans have the greatest ability to observe, compose, and internalize many complicated models of the surrounding world.

Intelligence and learned behavior are necessary for humans to maintain a social reality over the long-term. In the words of Ward Goodenough, "culture is the standards of behavior learned and understood by members of a society. Not all members of the society learn the same set or range of standards, and this distinguishes the membership is a various sub-groups of the society." The ability of mammal young, during socialization, to learn the behaviors appropriate for survival in their environment and in cooperation within social groups, is essentially the ability to obtain culture. This ability distinguishes these mammals from the "hard wired" biologically programmed behavior of non-mammals. There are many mammals that are solitary (i.e. a cat), and they do have learned behaviors, which they obtained during the dependency period. Social mammals, however, have the exact standards of learned behaviors.

Culture is, therefore, the complex that allows humans to maintain social reality over the long-term. This is not specific to humans, however, because all social mammals deal with the issues of communal living. During infancy, the child observes the world around him/her and internalizes the behaviors of adults. Children in social groups then play together, because play is the practice of adult behaviors.

Human culture, in the words of Ralph Holloway, is defined as the "imposition of arbitrary form on the environment." Stone tools, for example, are iconic, because they are of arbitrary shape. The mental ability to impose this shape on the environment is a result of the evolution of the cerebral cortex. Such neurological changes would not have been possible without changes in the mammalian reproductive system.


  • Goodenough, Ward H. "Culture." Blackboard. Web.
  • Holloway, Ralph L. "Human paleontological evidence relevant to language behavior." Blackboard. Web.
  • Jerison, Henry J. "Paleoneurology and the Evolution of Mind." Blackboard. Web.
  • Mann, Alan. "The Brain, Power Point Presentations 1 and 2." Lecture.