This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

Contribute Thoughts | Search Serendip for Other Papers | Serendip Home Page

Biology 202
2004 First Web Paper
On Serendip

In Search of the Neural Substrate of Humanity

Emily Hayes-Rowan

Introduction: Ontogeny Recapitulating Phylogeny

The idea that ontogeny recapitulates phylogeny is both a catchphrase and backbone of evolutionary study. I assume, in my search for the neural root of what we call "humanity," that this assertion is true, that the development of an individual organism in many ways mirrors the evolution of its species. If this is true, then there must be some point in human neurological ontogeny that defines us, a point at which our own development stops mirroring that of our closest mammalian cousins, the chimpanzee and other higher apes. At this point, our development begins to mirror the next leg of our phylogeny: the evolution of extinct hominids. Therefore, again, there must be a point in our ontogeny at which we separate from even the most recent of these ancestors. It is this point, the point in our ontogeny that mirrors the point at which we became fully human, or distinct in derived characteristics from our hominid ancestors, that must be derived from a specific neurodevelopmental event, likely the full maturation of a specific and unique brain structure. It is this point that can lead us to the neural substrate of humanity. What is this derived characteristic? Are there many? What are their neural correlates? This is what I hope to discover.

Human Development: Ontogeny ((1),(2))

I will use the evolution of a child's play to represent development in general cognitive function. I do this because as a child's play evolves with age it becomes increasingly symbolic. We will see that this symbolism is integral in finding the neural substrate of humanity.

From the age of eighteen months to approximately three years, a child's play develops within certain parameters. Toddlers are very physically oriented; they do not so much play as do. They imitate: people, dogs, birds, cars, anything exhibiting interesting actions or sounds. This imitation is not symbolic, however. The child is not pretending to be a dog. Rather, she is making the sound a dog makes. She is getting to know what "dog" is in her environment. This may seem to be a minor distinction, but it is an important one.

During the toddler phase, a child is also beginning to develop capacity for language ((3). This, too, follows a pattern of imitation and doing. The language of a toddler progresses from babbling and repetition to the expression of simple mental activities, like hunger, in simple verbal phrases, usually lacking syntax (i.e. "want milk"). This lack of syntax correlates with a lack of the full symbolic nature of language. The child is very oriented, both in speech and play, around the present. She imitates things she has recently seen or heard and names things within her immediate environment. She may recall these things from memory but her relationship with the world is not yet fully matured, and therefore her capacity for symbolic cognition is not fully developed.

Around age three, a child begins to play pretend. She is still tied to the present in that she needs props for her games; she does not mime a phone but rather needs a play phone in order to pretend to have a phone conversation. In this way, she is not yet fully removed from the constraints of time and place, as are cognitively mature humans. At this stage, the child will also begin to assume roles in her play, but they are ones of concrete and immediate importance: mommy, daddy, and baby. This development is significant because symbolic representation, or the association of meaning with arbitrary symbols, be they auditory or pictoral, is a capacity only of the evolved intellect ((18)). There is however some confusion between reality and fantasy. She is beginning to be able to leave the present in her games of pretend, but they are not sustained, they require props, and she does not cognitively distinguish them fully from reality.

It is important to the understanding of this stage to understand what is happening in the child's development of language. During this time, the child's language is becoming more complex, her syntax more complete. Show now expresses her desire for milk by saying, "give me milk," or "I want milk," sentences rather than a phrases, with subjects (one of them implied), verbs and direct and indirect objects. This is far more advanced than the "want milk" of a toddler. While this example does not correlate directly to the examples of play development above, the more complex language it represents does. One of the major results of human language is that it allows us to be free of present time and space in that we can discuss things absent, past, future, and intangible ((19)). This allows us to think (which we do in language) about what is going on, to project into the future the consequences of a present action, and to evaluate risk and benefit. In other words, we are freed, to some degree, from the reflexive and instinctive reactions of other animals. We are able to willfully control our responses to certain stimuli. If you extend this idea of freedom from the immediate, you will see the basic outline of how humans migrated out of the tropics, tamed the environment through agriculture, and developed art, religion, philosophy, etc. So again, while the "Give me milk" of a three-year-old may seem a menial developmental step, it is an important step on her path to full cognitive maturity.

The ages of four and five bring the culmination of the child's cognitive development. By the end of these phases, she has the basic capacity for mature human cognition; in other words, her capacity for symbolic representation is complete.

Around age four, a child's distinction between reality and pretend, which was cloudy at age three, solidifies. She begins to exhibit "sophisticated role-taking;" the family in a game will expand to include the dog and cat ((1)). She becomes less physically constrained in her play. She no longer needs a toy phone to hold an imaginary conversation, but may instead pretend that a banana or a block is a phone. Also, with the full language of her age, the child can engage in "cooperative play" ((1)) in which the idea for a game is communicated among and shared by all the players. Up until this point, play was "parallel;" while several toddlers may be playing in the same vicinity, they are not sharing their games. The full language capacity that comes around age four is integral in the development of cooperative play; the children can now express their own imaginings and plans to the others in order to engage them.

Age five sees more complex games of pretend and cooperative play, but also the important arrival of our final developmental step: the ability to solve problems verbally. At this age, children are able to communicate complex mental activity, like the desire for a toy (rather than a survival-basic like food) into words and use her words to obtain said toy (to solve a problem, namely not having the toy). To an adult, this seems an obvious use for language, but in the development of a child it is a huge step. Having developed the ability to use the full symbolic character of language in communicating about imaginary games and using language to solve problems, we will call the child, for our purposes, cognitively mature. There are many other steps in cognitive development leading to a fully mature adult mind, but for our purposes these can be ignored. We will see why shortly.

What We Know About Apes and Hominids: Phylogeny

The cognitive faculties of a human two year-old have been compared to those of a chimpanzee, in that both operate using a "general intelligence," or "simple, general-use computer program" about the world ((4). Like a two year old, a chimpanzee may know what a phone is and what a banana is, but neither would use a banana to represent a phone. Here, we see a divergence in the ontogeny and phylogeny of humans: There is evidence that our closest living mammalian relative is the chimpanzee, but very early in our own development (at age four) we diverge cognitively from this close relative. This means that the human capacity to "use" a banana as a phone (in other words, our ability to pretend or imagine) is a derived characteristic; it is not shared with our close relative. But is this characteristic derived only from the chimpanzee, or from our hominid ancestors as well?

This is not an easy question to answer. We cannot put an extinct hominid in a lab, expose him to bananas and telephones, and then see if he talks into the banana as he had seen people do into a phone. However, there is evidence we can use to deduce whether a hominid would have been cognitively capable of doing this.

Language is the tool I will use to deduce whether a hominid would have been capable of the banana/phone trick. I will do this in a round about fashion, without analyzing the endocasts of various extinct hominid species. Rather, I will use two major pieces of archaeological evidence to glean a general idea of hominids' capacity for language.

KNM WT 1500, or Nariokotome Boy ((5), is a hominid specimen that has clarified, for some, the issue of whether his species, Homo ergaster, was linguate (the word KNM WT 1500 expert Walker (6) uses to describe "having the capacity for full language.") It was originally thought that Brocca's area was sufficient evidence for linguacy in hominids. It was known that Brocca's area played some role in human language, and therefore it was assumed that a bump in the region of Brocca's area on a hominid endocast was evidence of language in that species.

Walker's study of Nariokotome Boy changed this hypothesis. With the advent of PET scans, it has been discovered that while Brocca's is involved in human language, it is not the only center of high metabolic activity during language tasks; in other words, Brocca's area is not solely responsible for language. This meant that Nariokotome Boy, though he had a Brocca's area, was not necessarily linguate. Close osteological study revealed that the foramen in 1500's thoracic vertebrae were significantly smaller than those in modern humans. This implied that Nariokotome Boy did not have the capacity for the complex muscle, specifically diaphragm, control needed to produce the full range of sounds involved in human speech. If he did not have the capacity for human speech, then he certainly did not have the capacity for human language. (6)

The next piece of evidence is the center of heated anthropological debate: the date of the appearance of anatomically modern humans. (I refer to the early members of our species as "anatomically moderns" in order to avoid entanglement in the Homo sapiens v. Homo sapiens sapiens argument (7).) Anatomically moderns have been dated by some as early as 100,000 years ago in Africa and Asia, where the evidence for this speciation is the appearance of tool industries not associated with preceeding hominid forms (7). The emergence of anatomically moderns in Europe is generally dated about 50,000-60,000 years later, when they replaced or evolved from Neandertals (7), (8)). For my purposes, I assume that anatomically moderns appeared at the later date, 40,000 years ago, subscribing to the school of thought that describes human evolution in terms of two "out of Africa" waves and implying that Homo neanderthalensis is a distinct and extinct side branch of human evolution, rather than direct evolutionary predecessors to H. sapiens. Within this context, while the appearance of bone and more advanced stone tool industries is evidence of higher cognitive function by their makers, this is not significant enough to place anatomically moderns at the dates coinciding with these tools (7). Rather, the event marking the appearance of anatomically moderns occurred in Europe around 40,000 years ago: what is known as a "cultural explosion" ((9)). In simplest terms, art appeared.

This is why art, rather than advanced tool making, is the defining behavior of anatomically moderns: Art is symbolic representation. Symbolic representation is a cognitive behavior possible only with fully developed language (also evidence of symbolic representation, as discussed in the section on ontogeny). Nariokotome Boy, who, remember, was not capable of human language, was a member of Homo erectus. In the timeline of hominid evolution ((10)), H. erectus is the species directly preceding H. sapiens. It has been concluded that the evolution of the human vocal tract, necessary for full speech and therefore for language, would have been slow ((11)). Also, as the appearance of the human vocal tract would be a derived characteristic, worthy of attributing any specimen with a human vocal tract to a species separate from H. erectus, I conclude that this species is H. sapiens. Anatomically moderns, and they alone, are capable of full human speech and therefore human language. It follows, then, that only anatomically moderns are capable of the symbolic representation, which removes them from chronological, special, and biological immediacy (see section on Ontogeny), and therefore are the creators of the art appearing 40,000 years ago. In other words, we have found our derived characteristic: symbolic representation and its resulting independence from chronological, special, and biological immediacy. This would have allowed for agriculture which emerged approximately 10,000 years ago ((12)), science, philosophy, religion, etc, all of which require language and the capacity for symbolic representation.

Conclusions: Recapitulation and Neural Correlates

I have demonstrated that symbolic representation, as manifested in art and language, is the derived behavioral characteristic of humanity, as it is the basis for all other things which we consider to be "human": science, math, philosophy, religion, theology, civilization (which is based on agriculture), etc. The appearance of full capacity for symbolic representation in human ontogeny (not until 4-5 years) implies that this capacity arose late in human phylogeny. I have demonstrated that this is indeed true, with the capacity for symbolic representation being a faculty of anatomically modern humans alone. I have discussed some behavioral manifestations of symbolic representation: language, art, religion, etc. This begs the question: If brain equals behavior, then what is the neural correlate of these behaviors? What is the neural substrate of these solely human behaviors?

Recent research has demonstrated that the human brain has no more cerebral cortex than would be expected of a primate of our brain size ((13)). However, the human encephalization quotient (EQ) is 7.44, which means that, for body size, humans are seven times as encephalated as should be expected ((14)). But simply having a lot of brain can't account for symbolic representation; there must be something unique about this large quantity of brain that is the correlate.

Significant research has been done on the prefrontal cortex in humans and great apes in an effort to discern differences. In 2001 Semendeferi et al. published their findings regarding Area 10 of the prefrontal cortex, one of the regions to which "higher cognitive functions such as the undertaking of initiatives and the planning of future actions" has been attributed ((15)). Semendefri et al. discovered that the GLI (gray-level index) of humans is unique among hominoids (humans and great apes). This means that humans have more room for connections among neurons that do the great apes. To me, this implies the following: that higher cognitive functions, facilitated by symbolic representation, arise from the huge number of connections in the human brain. Somehow, this must relate to, if not solely be, the neural substrate of humanity.

While research on the uniqueness of the human brain seems to be concentrated in the prefrontal and visual cortexes, I would assert that the temporal lobe may yield interesting findings, as well. Dr. V.S. Ramachandran is conducting fascinating research at the University of California, San Diego, about the role of the temporal lobe in human spirituality ((16), (17)). I have argued that the practice of religion is one of the uniquely human behaviors made possible by symbolic representation. As spirituality is the foundation of religious practice it is likely that some important findings regarding symbolic representation could result from further study of the temporal lobe.

I am in no way educated enough in the methods and knowledge of modern neuroscience to be able to draw a highly credible conclusion about what I am calling the neural substrate of humanity. In accordance with the research that I have done, however, it seems to me that all things which we consider to be human, all things we do in excess of survival, are facilitated by or directly associated with symbolic representation and language. It makes sense to me, then, that the neural correlates for these behaviors, being the result of a complex and advanced cognitive function, would lie in the areas associated with higher cognitive functioning, namely the frontal, and as I have suggested, temporal lobes. It seems, also, that the huge EQ of humans and the large degree of connection shown by Semendeferi et al. would have something to do with the generation of these higher functions.



1) Dehouske/Schomburg, educational chart on human cognitive development, Carlow College, 3/15/80.

2) Personal interview with Nancy Hayes, Masters Equivalent in Early Childhood Education, 2/26/04

3) The Development of Children, 2nd Ed, Michael and Shelia Cole. Scientific American Books, New York: 1993.

4) Patricia Greenfield, in The Prehistory of the Mind, Stephen Mithen. Thames and Hudson, New York: 1996.

5)Nariokotome Boy A description of specimen KNM WT 1500

6) The Wisdom of the Bones: In Search of Human Origins, Alan Walker and Pat Shipman. Knopf, New York: 1996.

7)Human Evolution: Summary of the Debate

8)Indiana University, Archaeology Page

9) The Prehistory of the Mind, Stephen Mithen. Thames and Hudson, New York: 1996.


11) "On the Nature and Evolution of the Neural Bases of Human Lanugage," Philip Lieberman. Published in Yearbook of Physical Anthropology 45:36-62, 2002.

12) a paper on the Neolithic Agricultural Revolution

13)Development of the Cerebral Cortex

14)comparative neuroatnatomy site on Serendip

15) "Prefrontal Cortex in Humans and Apes: A Comparative Study of Area 10," Katerina Semendeferi et al. 2001. Available at:

16) "A 'God-module' in the human brain?" Published in: Perspectives: A Journal of Reforme Thought v.14 n.2 (1999) p. 17, 23. Available at:

17) Phantoms in the Brain, V.S. Ramachandran, M.D., Ph.D, and Sandra Blakeslee. William Morrow and Company, Inc, New York: 1998.

18) Davis, Rick, November 22, 2002. Class notes from Anthropology 101 at Bryn Mawr College, Bryn Mawr, PA.

19) The Ape That Spoke: Language and the Evolution of The Human Mind, John McCrone. William Morrow and Company, Inc, New York: 1991.

| Course Home Page | Course Forum | Brain and Behavior | Serendip Home |

Send us your comments at Serendip

© by Serendip 1994- - Last Modified: Wednesday, 02-May-2018 10:53:06 CDT