The Book Of Humans by Adam Rutherford. Weidenfeld & Nicolson. Pages 258. Rs 599
Kuldip Singh Dhir
Adam Rutherford's book adds a cultural perspective to the gene-centric view of human evolution expounded by Bill Hamilton et al to make it a full package. He argues that we are not what we are as a consequence of genetic mutations. We have changed down the line not only via DNA but also due to our handing down acquired knowledge.
The cultural dimension is almost absent beyond the humans. Elementary behavioural similarities can be seen even in chimps but man alone is capable of progressive improvement, control and refinement. The non-humans cannot follow a train of thought, solve mathematical puzzle, reflect on metaphysics, analyse or create a work of art. He disagrees with Darwin that differences between us and the animals are one of degree and not kind. We have a culture that surpasses all others in sophistication.
It will, however, be futile to pinpoint a trigger for our evolution. Barring pivotal events like the birth of complex life through cellular fusion or the end of dinosaurs, life evolves messily and slowly. Our biological code is hidden in three billion letters of DNA spread over chromosomes. Gorillas, chimps and orangutans all had 24 chromosomes. We broke apart some six million years ago through a DNA mutation which crunched two chromosomes into one. This resulted in the new lineage of homo sapiens with 23 pairs of chromosomes which traces a line all the way to us. Subtle variations in the DNA make us all different. DNA changes randomly and the mutations may be detrimental to or beneficial for the survival of the organism. Over time bad mutations are weeded out and good ones spread.
The author has diligently explained prominent mechanisms of mutation like duplication, de novo gene formation, viral invasion and formation of enhancers. NOTCH2NL and SRGAP2 are examples of duplication and these relate with brain. More than 60 new genes have been identified in the last decade though we are not precisely clear about functions of many of them. The alien viral DNA is doing many things, one of which is the formation of placenta essential for successful pregnancy. HACNS1 is 546 lettered strip of DNA which works as an enhancer in the functioning of many tissues especially the forelimbs. Genes perform multiple functions. FOXP2 for example controls the growth of embryo. It is also known as language gene for the role it plays in conjunction with CNTNAP2. Language genes become useless in the absence of a highly structured hyoid, larynx, tongue, jaw, mouth and the psychological apparatus capable of perception, abstraction and description. Genes set up the frame work of speech, but vocabulary and grammar are the outcome of culture.
The author concludes that our brains got the firepower for language and speech 24 million years ago. Homo sapiens came into being 3,00,000 years ago and by 1,00,000 years ago we had bodies pretty much the same as we have today. Full language capabilities were in place by 70,000 years ago. We can see traces of modern skills and behaviour before the cognitive revolution witnessed 45,000 years ago, but these are sporadic blips only. The material culture took roots 40,000 years ago and by 20,000 years ago we have all that we call art and civilisation mainly through cultural transmission of the wealth of knowledge not encoded in our DNA. A refreshing and enlightening treatise indeed.