` The evolution of human beings is closely related to the evolution of the human brain. Brain capacity demonstrates how humans evolved from primitive to modern forms. By examining brain capacity across three different species of primates, namely Australopithecuas Africanus, Homo Habilis and Homo Erectus, it is possible to notice how brain capacity drastically increased, and with it, other modifications also took place, thus allowing modern humans (Homo Sapiens) to evolve into the present form. Based on primary research, this paper will examine brain capacity as a fundamental evolution characteristic, and will trace the transformations which took place from one stage of evolution to the other, noticing the correlated effects of this transformation, and the evidence of consequences at the level of the body and the transformation of the behavior of these primates.
The most primitive primate examined here is Australopithecus Africanus, an early species which lived approximately 3 million years ago, being the first species to be identified as hominin. The Taung specimen of Australopithecus Africanus refers to a natural endoclast consisting of a fragment of fossilized face, and a mandible which occludes with the maxillary. Taung was approximately 3 to 4 year-old when he died. The cranial capacity of this individual was 402- 407 cm3, when uncorrected for age (Falk et al. 2012). His brain size falls within the size for great apes, but presents a greater degree of encephalization, thus being recognized that the A. Africanus was a more evolved species than the earlier Paranthropus species (Falk et al. 2012). In their study of Taung, Falk and his team studied the metopic suture, which as compared to that of great apes, which typically closes immediately after birth, was not yet closed when Taung died (Falk et al. 2012). This particularity determined the authors to resemble Taung with humans, since “the MS normally becomes obliterated later in humans than in chimpanzees” (p. 8468). The authors claimed in their study that the metopic suture closure became an adaptive trait in human evolution. As Falk et al. (2012) showed, as bipedalism evolved in relation to increased neonate and adult brain size, the morphology of the birth channel determined a particular shape of the neonate. Consequently, the fontanelle and the metopic suture in human neonates are believed to be a direct result of the increased brain size, because this trait was necessary in order to facilitate the birth (Falk et al. 2012).
Homo Habilis lived between 2.4 and 1.5 million years ago, and as compared to the Australopithecine species, it featured a much larger brain capacity, more specifically, up to 45% larger than A. Africanus examined above (Tobias 1987). Arguably, it was with H. Habilis that the Homo characteristic of disproportionate brain expansion emerged (Tobias 1987). H. Habilis featured increased frontal and parietal lobes, which is a characteristic of the Homo genus. Research has also showed that the areas of the brain which are responsible for speech development are well-represented in H. Habilis, which is also an important development which does not appear at the earlier species. The brain of the H. Habilis is overall much more complex than that of the Australopithecine species. As Tobias (1987) revealed, “with H. habilis, cerebral evolution had progressed beyond the stage of “animal hominids” (Australopithecus spp.) to that of “human hominids” (Homo spp.)”(p. 741). In particular, the emergence of a structural marker which formed the basis for speech represented an aspect of evolution which clearly represented a crucial stage in the human development.
Research clearly indicated that H. Habilis had a higher brain capacity than the A. Africanus, described earlier. In his research, Holloway (1980) examined the brain endoclast of Olduvai George, a H. Habilis specimen (O.H.7). This specimen represented in 1967, the basis upon which the existence of H. Habilis was proved. While early research tried to associate this specimen with A Africanus. However, its larger capacity determined researchers to state that such a great excess is unlikely. Holloway (1980) determined that O.H. 7 had a brain capacity of approximately 700 ml. However, in this case, the poor condition of the parietals which were partially destroyed, and the low amount of bone preserved meant that these structures were not useful in estimating the brain capacity. For this reason, Holloway (1980) used a multiple regression technique based on measurements taken from other endoclasts in order to estimate the specimen’s brain capacity. As Holloway (1980) showed, “the multiple regression analyses give a wide range of values, depending on the samples chosen and their constituent members” (p. 2731). Despite these admitted problems, the reconstruction of the parietals based on multiple regression analysis was useful in determining that O.H. 7 had a much larger brain capacity than A. Africanus, and thus represented a leap in evolution.
Finally, Homo Erectus was an important species of hominins which lived for more than a million years and gave birth to multiple subspecies. This species is dated from1.9 to 70, 000 years, and is considered a close precursor of the modern species. Thus, the brain of the H. Erectus represents a fascinating insight in human development, both because this species dwelled on Earth much more than modern humans have existed, and because they are closer to H. Sapiens As Rightmire (2012) showed, there are plenty crania, mandible and teeth from H. erectus specimens, particularly as compared to older species of hominines. There are more than 30 intact crania available for research. As compared to modern humans, the braincase is broad and low (Rightmire 2012). Furthermore, there is a poor fitting between the relatively small brains which is fitted insight a huge cranial case (Right 2012).
In their research of the Mojokerto child who lived 1.8 million years ago, Coqueugnoit et al. (2004) showed that the brain growth during childhood is an evidence of evolution. As the researchers found, the Mojokerto child was about 1-year-old when he died, and his brain capacity was approximately 636 to 730 cm3, which represents 72-84 % of that of an adult H. Erectus. Because hominids have larger skulls than primates, they face the challenge of developing large brains against physiological size constraints at birth (Coqueugnoit et al. 2004). This is solved by having smaller skulls at birth. At 1 year, human brains are 50% the size of adults. Data obtained from this specimen showed that brain maturation after birth was much lower than in humans. This shorter period of growth in the social environment also meant that Homo Erectus’s cognitive skills cannot be compared to those of human beings, and also, that complex spoken language evolved much later in human evolution (Coqueugnoit et al. 2004).
Therefore, by studying the skulls of early hominins and primates, it is possible to establish the development pattern of the brain. Brain size, a defining human trait, developed progressively from one evolutionary stage to the other. As shown throughout this paper, the development of brains size also determined other changes in physical of the characteristics and cognitive abilities. Thus, whereas Taung, the A. Africanus specimen had metopic suture which suggests higher flexibility of the bones as an adaptation to the larger brain, in H. Habilis, there is evidence of physiological changes which suggest that the possibilities for spoken language were beginning to emerge. Moreover, in H. Erectus, the specimen examines proved that the child’s brain continued to grow, although its size and capacity are not comparable to those of humans. This data provides an understanding of the processes which lead to the development of specific human intelligence.
References
Coquugnoit, H., Hublin, J., Houet, V. & Jacob, T. (2004). Early brain development in Homo erectus and implications for cognitive ability. Nature 431(7006): 299-302.
Falk, D. et al. (2012). Metopic suture of Taung (Australopithecus Africanus) and its implications for hominin brain evolution. Proceedings of the National Academy of Sciences of the United States of America 109(22): 8467-8470.
Holloway, R. (1980). The O.H. 7 (Olduvai George, Tanzania) hominid partial brain endocast revisited. American Journal of Physical Anthropology 53, 267-274.
Rightmire, P. (2013). Homo Erectus and Middle Pleistocene hominins: brain size, skull form, and species recognition. Journal of Human Evolution 65, 223-252.
Tobias, P. (1987). The brain of Homo Habilis:a new level of organization in cerebral evolution. Journal of Human Evolution 16(7-8): 741-761.
