The (mon)Keys of Evolution

by Jordan Pennells

The human evolutionary timeline is a contentious topic within academia, repeatedly being revised with the development of genetic technologies. A common misconception is that we evolved from Chimpanzees. This idea is somewhat incorrect in the sense that (it is theorised that) both species evolved from a common ancestor between 6.5-7 million years ago, according to calibration of genetic mutation rates. The Chimpanzee is human’s closest relative, sharing 98% genetic similarity (note: when considering the genome sequence as is without including regulatory elements). This value may seem disconcertingly high, but considering the 3 billion plus base pairs in our genome, there still is scope for the significant degree of variation between species that we are accustomed to.

Conserved regions confer the proteins for vital biochemical processes, general structural elements and organ development; essentially preserving the similarities that we see between great apes and ourselves. Varied regions, however, are an evolutionary device that have allowed us to all but disentwine ourselves from the predacious web of nature. The human race has developed towards an advanced global civilization, capable of feats such as releasing specialised objects into our planet’s orbit that track our precise geographical location, and creating a virtual community containing the entirety of human knowledge, which we undoubtedly couldn’t live without.

But what makes us human? What are our features that have defined our cognizance and propelled us to the apex of the food chain? The evolutionary development that has allowed for our speciation from apes has occurred in a multitude of genetic steps over a millennial timescale. Looking back at the culmination of the major physical traits (phenotypes) that have emerged since the speciation of ancestral humans, the main features include:

  1. Bipedalism – evidence of the shift from 4-limb locomotion to upright walking has been seen to originate in paleontological findings of the prehistoric species S. tchadensis, which existed approximately 6-7 million years ago. Compared to previously classified primordial apes, a shift in the location of the foramen magnum (the hole in the base of the skull through which the spinal cord passes) further towards the underside of the cranium indicates that anatomically, this species would have held its head on an upright body.
    s_tchadensis-reconstruction

    Reconstruction estimate of Sahelanthropus tchadensis based on cranial fossil evidence

    Evolutionists, pioneered by Charles Darwin in his book The Descent of Man, have theorised that bipedalism was driven by the selective desire of freeing up the arms during walking, and has been linked to the establishment of monogamy. As a result of climate change, African jungles became seasonal ecosystems, which necessitated the use of unoccupied arms to carry a bounty of food back to an abode. A mutually beneficial deal was struck between males and their female partner, who was tasked to care for their offspring. If the male provided food, collected with their free arms, the females would mate solely with their provider. Although this notion is difficult to confirm, a recent study into Chimpanzee behaviour concluded that they would walk upright to carry valuable resources away from competitors. If you aren’t convinced, take a look at this Chimpanzee carry 12 oranges at once!

  2. Cranial volume – the next phase of human evolution comes in the form of the ‘explosive’ growth (termed as such if you’re in a conversation with an evolutionist) of the skull volume, scientifically known as encephalization. Skull volume, and therefore brain size, has as much as quadrupled from the prehistoric S. tchadensis to us Homo sapiens, as is evident from Paleoanthropology discoveries.
    brain-size-graph

    The evolution of prehistoric human’s skull volume

    Brain development allowed for improved cognitive ability (although it should be noted that brain size does not directly indicate improved cognition, with subsequent spatial specialisation within the brain playing an important role). A distinctive difference between apes and humans that allowed for the increase in brain size is the loss of excess body hair. The vast amounts of proteins fixed in creating abundant hair follicles and keratinised hair fibres could be recycled and put to better use within the brain. Although there is an extensive amount of research that delves into evolutionary-based neuroanatomical development, one of the conclusions is that the vast number of polygenic mutations developing the brain resulted in advanced tool-making capabilities and the emergence of language.

  3. Language – the development of communication in prehistoric humans provided an immense selective advantageous towards the hunting and gathering of edible food, warning of impending danger and creating interpersonal connections that provides a glimpse into the beginnings of society. The predominant physical trait that allowed for the creation of sound within a favourable vocal range to form communication is theorised to be the descent of the larynx over time (however, this theory is difficult to confirm without fossilised evidence).Of course, the evolution of language consists of more than physiological change, with the neurological ability to use this evolved vocal tract being an extremely complicated subject that still in large remains a mystery to us.

Stay tuned for a dive into the evolutionary genetics of spoken word, and how this can relate to us in the modern day.

 

Sources:

Carroll, Sean B. “Genetics And The Making Of Homo Sapiens”. Nature 422.6934 (2003): 849-857. Web.

Jobling, Mark A, Matthew Hurles, and Chris Tyler-Smith. Human Evolutionary Genetics. 1st ed. New York: Garland Science, 2004. Print.

“Sahelanthropus Tchadensis | The Smithsonian Institution’s Human Origins Program”. Smithsonian National Museum of Natural History. N.p., 2017. Web. 10 Jan. 2017.

Wayman, Erin. “Becoming Human: The Evolution Of Walking Upright”. Smithsonian. N.p., 2017. Web. 10 Jan. 2017.

 

 

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