There are those who seek to deny that Homo sapiens are descended from African apes. This post will demonstrate once and for all that the man did indeed evolve from apes, and that we are still apes. Going by comparative morphology, our anatomy is most similar to the great apes (see Fig 1). Genetically we are most similar to Pan troglodytes (chimpanzees), with only 1.6% difference in our genes (Diamond, 1991).
There are some differences of course between humans and chimps. One of which is brain size (measured in cubic centimetres). Chimpanzees have a cranial capacity of 300-400 cc (Macdonald, 2009) while humans have a much larger cranial capacity of 1100–1900 cc (Wikipedia, accessed 2012). From this we can draw a simple hypothesis: If humans evolved from apes, we should find evidence of an increase in cranial capacity over time in the fossil record.
We can make cranial endocasts of fossil hominins which can be used to give a good estimate of cranial capacity (Johanson, 2006). If we plot the age of the fossils against cranial capacity on a graph, we see very clearly that there was a trend over time towards larger brains (see Fig 2):
This indisputably shows that there is a trend towards increased cranial capacity over time in the fossil record.
We also have genetic evidence to corroborate this. There is a gene called ASPM, which can mutate to cause microcelphaly (a disorder which causes humans to have a greatly reduced cerebral cortex) – from this we can hypothesize that ASPM has something to do with the development of our uniquely large cerebral cortex. When scientists compared the ASPM gene with other species there was clear evidence that it had undergone natural selection in our lineage (because of the number of changes in the coding sequence) (Zimmer, 2005).
Another thing that we’d expect to find in the fossil record is species that show a mosaic of features between humans and apes. The most obvious example of this is Australopithecus afarensis. Who had a cranial capacity of between 375 and 550 cc (Talk Origins, accessed 2012) – which is about that of a chimpanzee. Yet we know that A. afarensis could walk on two feet, like a human. This can be seen from the anatomy of their pelvic structure and their feet (Wikipedia, accessed 2012). We even have fossilized footprints of A. afarensis which show beyond doubt that they walked on two legs (see Fig 3). What we have is a chimp-like creature that walked on two legs like a human. What could this be if not a perfect example of mosaic features in an evolutionary transition?
The truth is abundantly clear; Homo sapiens did indeed evolve from African apes. Its also worth bearing in mind that I provided the merest examples of the kinds of evidence we have for this, if you wish to see just how well supported human evolution is, I would recommend reading some of the books listed in the references.
For any creationists who might be reading this, I shall leave you with a challenge. Take a look at Fig 4 and tell me which of these specimens are human and which are apes. Let me know in the comments below.
DIAMOND, JARED (1991), Rise and Fall of the Third Chimpanzee, Great Britain: Radius
JOHANSON, DONALD & EDGAR, BLAKE (2006), From Lucy To Language, New York: Simon & Schuster
MACDONALD, DAVID W. (2009), The Encyclopedia of Mammals, Oxford: Oxford University Press
ZIMMER, CARL (2005), The Smithsonian Intimate Guide To Human Origins, New York: Harper
Talk Origins. Hominid Species. Online. Available from: http://www.talkorigins.org/faqs/homs/species.html#afarensis [Accessed 21 January 2012]
Wikipedia. Australopithecus afarensis. Online. Available from: http://en.wikipedia.org/wiki/Australopithecus_afarensis#Skeletal_morphology_and_locomotion [Accessed 21 January 2012]
Wikipedia. Cranial capacity. Online. Available from: http://en.wikipedia.org/wiki/Cranial_capacity [Accessed 21 January 2012]