What is it makes us human?

It is well know (and extremely misleading, as I shall show) that human beings and chimps are more than 98% the same genetically. It is true but we need to understand what this means. A gene is something that has a particular effect, usually to make a protein or to control other genes. One way in which we can say that two genes are the same is if they do the same job. There is gene that makes the vital protein hormone insulin. All mammals have the gene to make insulin. But the insulin and its gene are slightly different in DNA composition in different species even though they do the same job. The easiest way to understand this is to go back before the era of modern genetic engineering. The insulin injected to treat diabetes used to come from cows, pigs or sheep. It was a by-product of the meat industry. These animal insulins function correctly in human beings but they are not identical in composition because the DNA has a few substitutions in its bases. Most of the genes in human and chimps have the same functions but they differ in a few bases in the way that the animal insulins differ from human. These small genetic differences must be responsible for the profound and stable differenecs between the two species.  

Insulin shows us that these occasional substitutions often have no significant effect. But we also know that a single base change can sometimes have a dramatic effect: cystic fibrosis is caused by a single base substitution. Besides having these crippling negative effects, small changes can sometimes have large positive effects. 

The Foxp2 gene is a major research focus for human/chimp differenecs. This came to light from studies of a family with speech defects running through several generations. This was traced to a break in a gene, Foxp2, which is found intact in all animals with only minor differences between them. Human Foxp2 differs from chimp Foxp2 by only two amino acids and mouse by only 3. DNA from Neanderthal man shows that they had the same Foxp2 gene as us. 

Foxp2 is a transcription factor with many effects besides speech. It is necessary for lung development in mice and it is involved in the development of birdsong. It is clearly a vital gene and the suspicion is that those two amino acid substitutions compared to the chimp have enabled the great gift of human speech. Probably many other genes are also needed to perfect human language but Foxp2 seems to be a necessary if not sufficient condition. 

As genomics develops, more such correlations between genes and body structures and behaviour will come to light. We will then know just what the significant tiny differenecs are that make us Not a Chimp, as a forthcoming book by Jeremy Taylor puts it.