Cognitive thought processes that arise from consciousness are depicted as being an exclusive human characteristic. Reflected in the metaphysical views from Aristotle (384-322 BCE) to Rene Descartes (1596-1650), the philosophical implications for our species result in an unbridgeable chasm between our species and the rest of the animal kingdom. These geocentric and anthropocentric depictions of our species would be irrevocably damaged by the theory of organic evolution by Charles Darwin (1809-1882). With evidence refuting the traditional view of our species held by both philosophers and theologians, speculation as to our relationship with other primates began a critical point of inquiry. Inquiry into this relationship by Thomas Huxley (1825-1895) provided critical evidence in support of his pithecometra hypothesis, whereby he stated that our species is closer to the great apes (orangutan, chimpanzee, and gorilla) than the two lesser apes (gibbon and siamang). In further support of Huxley’s hypothesis via embryology, Ernst Haeckel (1834-1919) concluded that not only does our species resemble other primates, but we share a common ancestor in the form of the illusive “missing link” that was speculated to be found in Asia. These scientific inquiries supported Darwin’s claim that our species differs from other primates in degree and not in kind. These differences in degree can be extended to anatomical, physiological, and cognitive functions of the primate brain. Such bold statements would require evidence from the fossil record.
Though Darwin and Haeckel differed regarding the geographic location of human evolution (Darwin supported Africa, whereas Haeckel supported Asia), the search for fossil evidence resulted in the successful discoveries of fossil hominids in many areas of the world. Discoveries and interpretations by Davidson Black (1884-1934), Robert Broom (1866-1951), Raymond Dart (1893-1988), Eugene Dubois (1859-1940), Donald Johanson (1943-), and the Leakey family (Louis, Mary, Richard, and Meave) have contributed crucially needed evidence to aid in reconstruction our species’ phylogenic past. Though the fossil record is far from being complete, the accumulated evidence can suggest an evolutionary descent as speculated by Darwin. Utilizing cladistic analysis, our species’ phylogeny is speculated as having the following relationship: Australopithecus afarensis gave rise to A. africanus, which then split into two branches, one leading to Homo habilis and the other leading to A. robustus/boisei. Our species, whose descent is from the Homo line, can trace its origin back to these primitive hominid forms.
Our relationship to other primates extends back further than these hominid forms. The discovery of the fossil Proconsul indicates a common ancestor dating back 18 to 20 million years ago. Further back in time, around 40 million years ago, there was a split between New World and Old World monkeys. An additional split between Old World monkeys and apes had occurred around 35 million years ago. Of the great apes, it is speculated that there was a split that was ancestral to the orangutan around 16 million years ago and the gorilla split from the chimpanzees around 8 million years ago. The most recent split between hominids, the third chimpanzee, and both chimpanzees (common and pygmy) was as little as 6 million years ago. Supported by both immunology and molecular methods, the DNA hybridization indicates and vindicates the fossil record, whereby the human primate is closer to the chimpanzee and gorilla than any other primate. In fact, our species shares 98% of our DNA sequence with our chimpanzee cousins. However, it must be noted that sharing 98% DNA does not confer or equate that our species is exactly the same; a similar misconception applied to the Darwinian model of evolution erroneously states that our species descended from the chimpanzee and not the fact that our species shares a common ancestor. Just as cranial capacity does not confer complexity, the sharing of common genetic material does not confer exact characteristic and behavior shared by all primates. Our species does resemble the chimpanzee (and other apes) in both in anatomy and physiology, same dental formula (2-1-2-3), close embryonic development, and a degree of mental capabilities and behavior. However, does 2% make a difference, not only in morphological features, but in the degree of complexity of the brain? Regardless of the percentage held to be in common, the evolutionary differences among the primate brain (in terms of reorganization) is evident; yet it does produce an affinity between our species and our cousin, the chimpanzee. The exact circumstances surrounding the evolution of primate brain is a point of speculation; however, certain anatomical and physiological features that coincide with cranial expansion may give the necessary indications as what factors may be responsible.
The exact nature surrounding the advancement of the primate brain is continuously a source of inquiry. Random mutations, changes in diet, environmental factors, and bipedality are the most speculated influences that are implicated in the evolution of the brain. It is the contention of this author that morphology features of the cranial base hold determining factors as to the degree of bipedality and an indication of efficiency concerning the anatomical changes between bipedality and cranial capacity (inferring complexity). Such efficiency would translate to an enlarged cranial capacity that is capable of sustaining the advanced hominid brain. These revolutionary changes in morphology that had occurred during our species’ evolution are reflected in both cranial (and postcranial) and endocranial casts of these early hominid forms. The evidence appears to support this author’s speculation and other scientific evaluations. What the endocasts had revealed, starting with A. afarensis, was the presence and location of the lunate sulcus and frontoorbital sulcus, all of which indicates an emergence of an advanced hominid brain. Though there is much controversy as to their interpretation, regarding it being more ape or human in appearance, the emergence of a “humanlike” Broca’s area and development of the prefrontal cortex suggests that a rudimentary form of language and associated skills was used by the H. habilis stage in human evolution, all of which indicates the development of cerebral symmetry.
A degree of symmetry can be found in all primates, though our species expresses the greatest degree. These characteristics, along with morphological features of the cranium, can give an indication as to our ancestral behavior. If bipedality and endocranial casts indicate a trend to a more humanlike appearance, perhaps the behavior suggested by Odeodontokeratic, Oldowan, and Mousterian cultures are well-founded. Furthermore, if research correctly indicates the degree of complexity and similar physiology (brain) of our primate cousins, any remaining anthropocentric attitudes concerning our place in nature would have to capitulate for the lack of scientific evidence and reason. Our species, as Darwin indicated, differ only in degree and not in kind. The progression by which these changes in various portions of the brain occurred and are sustained is grounded within biological processes of evolution.
Advancements in the hominid brain that resulted in phylogenic change are due to random mutation and the selective forces of environmental factors and behavior. The genetic sequence that resulted in the advanced hominid brain are due to random nucleotide base changes, whereby nucleotides that contain methylated cytosine control the rate by which mutations occur, via insertions, deletions, and structural sequencing. Though in a constant state of genetic flux, the phenotypic expressions that translate into the hominid brain are speculated as being a result of the stochastic nature stemming from the founder effect. These mutations most likely changed the composition and function of brain peptides and fostered great cytological alterations (reorganization). This resulted in both an enlarged cerebral cortex and asymmetry, which allowed for “human” characteristics of language, dexterity, and other distinctly human behavior patterns. Once expressed, these phenotypic changes of an enlarged brain, neural reorganization, and behavior are then offered to the selective forces of evolution.
Though random genetic shuffling created the advanced hominid brain, sustaining this “new adaptation” would require positive outcome when offered for selection. The advanced hominid brain (multifarious rational thought), bipedality, and complex behavior allowed for our ancestors to manipulate their environment and broaden their dietary base. The environmental factors surrounding these hominid forms indicate few predators in a semiarid climate, with sporadic open woodlands, bush, and grassy savannahs. These roving bands of hominids, utilizing their evolutionary and revolutionary cerebral adaptations, migrated, occupied, and successfully adapted to different environments. With an increase in diurnal hunting activities (including higher efficiency) and later the use of fire, the increase in particular meat consumption (liver) would affect Ca” levels in the bloodstream. High levels of Ca” would influence synaptic response, resulting in greater memory and learning capabilities. In addition, meat proteins, which contain amino acids of tryptophan, tyrosine, and lecithin, would affect the performance of neurotransmitter activity. Essentially, behavior that influences diet will influence neurotransmitters, which then in turn influences behavior. Together, this cyclical process not only contributed to the sustaining of any genetic advancements of the hominid brain but also aided in the direction of its evolution toward greater reorganization. Considering these processes, the arbitrarily set traditional “Cerebral Rubicon” of 750 cc, as posed by Sir Arthur Keith, must be rejected in light of recent scientific advancements. Such distinction between complexity and cranial capacity serves to illustrate the obscurity of that defining moment of becoming “Homo” within our hominid ancestry. Furthermore, our close affinity with the other great apes forces our species to reconcile its metaphysical views concerning our own place within nature. Only with such naturalism within an evolutionary framework can our advanced hominid brain allow the discovery of its true humanity in ourselves and, to a lesser extent, the other primates.
Though the evolution of the advanced hominid brain, as with evolution in general, is accepted by the scientific community, there are contentions as to which evolutionary model correctly depicts this evolutionary process. In Darwinian evolution, the rate of change is slow or gradual. Regardless of population size, sympatry or allopatry provides unidirectional phylogenic change toward phylogenic speciation. Contrary to this view, the punctuated equilibria model of evolution, as postulated by Eldridge and Gould, states that environmental changes spur highly episodic rates of change of small and isolated populations. It is the survival of stochastic changes that results in allopatric speciation. In a synthesis of these perspectives, the advanced-brain model of evolution, as postulated by Bennett Blumenberg, states that the episodic and unidirectional change on isolated populations resulted in the survival of nonrandom stochastic expressions. Similar to punctuated equilibria model, survival of stochastic changes results in allopatric speciation. In this manner, once the advanced hominid brain emerged from the process of evolution, the symbiosis between our species’ physiological process and expressed behavior had a directional impact on the accumulative complexity or reorganization of our ancestral brain. As if by design, but certainly not, the greater degree of mental capabilities allows our species not only to discover the processes by which it was derived but also to understand and direct its own future.
As there is evolution, so too is there extinction. These two aspects of the same evolutionary coin reveal not only our origin but also the future of our species. In this manner, extinction becomes a real possibility, if not an eventuality. Our advanced primate brain, an overspecialized product of evolution, has interred within its evolution a responsibility toward its environment and the rest of the animal kingdom. In regarding our primate relatives, greater care and diligence should be taken in order to both conserve their natural habitat and to ensure their prosperity and longevity; for if 6 million years ago, the DNA difference of 2% produced different results than today, it would be interesting to speculate on our own primate’s future and final outcome. Such speculation should indicate both the chance and consequences of evolution. Furthermore, environmental conservation guided by reason should regulate the extent of our modifying activities of the external world. Excessive modifications of the environment can lead to critical thresholds and total collapse of ecological systems. With the unity of life on this planet and the intricate symbiosis among species, it would be in the best interest of our species to reduce these environmental problems down to a minimum. This will help to ensure the survival of our species, all of which propels the evolution of our species into the future.
With advancement made in the areas of genetics and the cognitive sciences, the mysteries of the human brain and cognition are beginning to become demystified. The nature of the relationship among sensory receptors and logarithmic processes of mental processes are being explored by revenant computer simulations provided by science. Such advancements in computer technology, which is in itself a recent product of the primate brain, can not only simulate the mathematical process of organic evolution but also reflect the mental processes that created it. Innovations in artificial intelligence, genetic engineering, cloning, and environmental changes (both controlled and uncontrolled) will certainly challenge the regality of our primate brain. With rapid advancements in technology stemming from our complex brain (more rapid than the evolutionary process that produced the biological foundation for their development), the next evolutionary change is a point of curious speculation, for the future can lead to the evolutionary direction as envisioned by Arthur C. Clark’s 2001: A Space Odyssey or Friedrich Nietzsche’s Ubermensch. Evolution or exoevolution (as postulated by H. James Birx), our species now has limited control over the direction of its evolution, all due to the evolution of the primate brain.
- Birx, H. J. (1988). Human evolution. Springfield, IL: Charles C Thomas.
- Buss, D. M. (1999). Evolutionary psychology. Boston: Allyn & Bacon.
- Corballis, M. (1991). The lopsided ape: Evolution of the generative mind. New York: Oxford University Press.
- Corballis, M. (1999). Phylogeny from apes to humans. In M. C. Corballis & S. E. G. Lea (Eds.), The descent of mind: Psychological perspectives on hominid evolution (pp. 40-70). New York: Oxford University Press.