Human Evolution - We are a walking ecosystem

We are quite similar to the African apes anatomically and genetically, especially to the chimpanzees and bonobos. Humans have 46 chromosomes in their cells while all of the great apes have 48. In reality, this difference is not as great as it would initially seem because the human chromosome 2 is a fusion of ape chromosomes 12 and 13 with most of the same genes.

Research on learning the entire genome of common chimpanzees was completed in 2005. A comparison between this and the human genome (completed in 2001) shows that 96% of DNA base pair sequences of humans and chimpanzees are the same. Most of the 4% difference is in duplicated non-gene segments. If only gene segments are compared, there is a 98% similarity. The genes that differ mostly control speech, smelling, hearing, digesting proteins, and susceptibility to certain diseases. These dissimilarities are to be expected given that we have been on essentially separate evolutionary tracks for 6-7 million years. During that time, we have been subject to somewhat different natural selection pressures. These differences led to bipedalism for our ancestors along with a much larger brain and, ultimately, speech.

A comparison of DNA nucleotide sequences of living primate species show that humans are most closely related to the African apes. Next in descending order of genetic closeness to us come the Asian apes, Old World monkeys, New World monkeys, tarsiers, and finally the lemurs and lorises. This genetic comparison corresponds exactly with a comparison of homologous primate physical traits. It also fits nicely with what we know from the fossil record. The prosimians were the first to evolve. Next came the monkeys, then the apes, and finally humans.

Dr. Dennis O'Neil Behavioral Sciences Department, Palomar College, San Marcos, California