Ancestors in Our Genome: The New Science of Human Evolution by Eugene E. Harris
My rating: 4 of 5 stars

Who Da’ Daddy?

Palaeontology and genetic biology are not for intellectual sissies. Nuclear physics may be hard for the layman to understand, but the developmental history of our species is a subject of equal complexity, with at least as many unsolved mysteries. And Harris lets us know about these without mercy.

If you thought that Darwinesque Natural Selection was all you needed to know about evolution, forget it. Its far more complicated than that. While reading Harris I found it useful to consider genetic analysis as a sort of quantum physics in reverse. The basic building blocks of analysis are genetic mutations, random alterations in DNA, which are like quantum events. Whereas physicists work forward from the events to their consequences, genetic researchers work backwards from how things stand now to the underlying events. Both disciplines have the problem of connecting their elementary events to the world as we see it - the physicist to the non-quantum world of perception, and the geneticist in the existing morphology of our species.

And this connection ain’t easy to make. As Harris says, “The field of genetics has not, by and large, been able to determine the exact genetic basis for most morphological features. When we are comparing DNA nucleotides we know when we are comparing apples with apples or oranges with oranges. With morphological features, one could very well be comparing apples with oranges.” There are an enormous (infinite?) number of ways that a feature, like a bone or a shape, can be genetically generated. Gene mutations have complex interactions with each other. Thus, for example, the mutations promoting large human brain size occur with others that reduce the size of the digestive tract which has also been adapted to process cooked meat. The result is an animal with sustainably high energy consumption... that talks; and thanks to yet another mutation, sweats over its entire body.

So there are differences in species-trees (the classification of evolutionary forebears by what they look like and who can mate with whom successfully) and gene-trees (the apparent sequence of evolution of mutations themselves). Sorting these differences out involves some complex logical analysis which takes into account things like Homologous vs Homomorphous traits, Gene Coalescence, Parapatric vs Allopatric (or even Sympatric!) speciation, Internode Times, Effective vs Census Populations, Junk DNA, and Genetic Drift. As I said: not for sissies.

So although some things about human evolution are fairly clear - like our separation from chimpanzees about 5 million years ago; and that about one third of our genetic material is shared with more primitive apes - it’s not all that certain who are our cousins and who are our grandparents. Even with the completion of the genome mapping for many of the relevant species, and the application of substantial computing power, no one really understands the route from forest ape to human biped. In fact genetic science itself casts a shadow on some of the most basic concepts of evolution: “the question of exactly how to define a species, remains a conundrum for biologists.”

There are also some other intriguing questions raised rather than answered by recent advanced research. For example, how a relatively small population of our genetic forbears got the jump on other larger populations which might also have resulted in humanoids. Or why the fossil record along with DNA analysis shows an almost catastrophic decline in the population of some fairly recent groups of our ancestors. Apparently we are not very good genetic adapters during our trek(s) out of Africa.

It’s all more than a bit like the television show Who Do You Think You Are but on a level of the species. Instead of finding out that great great grandpa was a drunken brothel keeper, we discover that our supposed superiority as a species is really just hubris. For example: our defective DNA is what allows us to contract AIDS and dementia while chimps and gorillas don’t. Rats and many other ‘inferior’ animals, it turns out are far better equipped genetically than humans to adapt to environmental changes. So where we sit on the hierarchy of species is really only a matter of what scale one chooses. Since other apes aren’t typically given a vote... well, it’s rigged ain’t it?

This is a serious book for non-specialists. Harris writes clearly and there is a logical development to the whole. But he doesn’t spoon feed the material. So be prepared to pay attention if you pick it up. Or alternatively... wait until you’re a bit more evolved.

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