We *Are* Apes, Silly!
If you do happen to be a member of that anachronistic group that still hasn't learned this fact yet, I'll explain just one of the many ways we know. We used to have vitamin C synthesis genes, but as we switched our diet to include more fruit we no longer needed these genes to produce vitamin C. The energy spent producing the enzymes needed for vitamin C production could have been better spent doing something else, such as finding food or pursuing mates. So losing the complex vitamin C synthesis pathway resulted in a survival advantage once we had plenty of vitamin C in our diet.
Studying information enables us to compare different species and observe the exact DNA differences between them. Vitamin C is a vitamin because it is essential, but it is not produced naturally by our bodies. Many species still have the genes for producing vitamin C. We know the pieces of machinery that are involved in its biosynthesis, and we know which DNA sequence makes these pieces of machinery. When humans had their DNA sequenced, scientists found relics of vitamin C biosynthesis genes. A broken gene with no function; still mostly intact but riddled with a number of mutations. When the DNA sequences of other simian primates are sequenced, not only do we find the same broken gene, in exactly the same place, we find the same mutations too. This is just one of many excellent pieces of evidence that show that humans and other apes share the same common ancestry.
But the story goes deeper. There are other primates that still have vitamin C genes intact - such as tarsiers and members of the strepsirrhini sub-order. These primates eat mainly insects, and we higher order primates eat more fruit. Fruit is rich in vitamin C, insects are not. We know that the last common ancestor that we shared with insect eating primates was approximately forty million years ago, as ascertained by dating the fossils which connect us and them. It appears that around forty million years ago primates switched from a vitamin C poor diet to a vitamin C rich diet. As there was no longer any evolutionary pressure on the vitamin C producing gene, mutations accumulated because detriment of this gene no longer affected survival rates.
What biological studies show is that we share EXACTLY the same broken gene, in EXACTLY the same position, on EXACTLY the same chromosome, with EXACTLY the same mutations, in EXACTLY the same positions in the gene. This is even more remarkable when we consider how big the human genome actually is; we have more than six billion base pairs. This is precisely what we would expect from common ancestry. The fact that the genes correlate with feeding habits is both the icing on the cake and the cherry. Moreover, it isn't just this broken gene with which we see common ancestry. Genetic homologues are the same for almost every single gene in the human body. Of the 22,500 genes in the human body, every one that has ever been used in comparative genomic studies shows EXACTLY the pattern expected.
That's the rub folks - we may be very intelligent apes, with fecundity and awareness unlike any other primates - but we are apes nonetheless!
