A Natural History of Ourselves (1)

By Hannah Holmes.

“Whenever biologists discover a new animal it’s their custom to crank the creature through a factual sausage grinder, producing tidy links of information. With academic detachment they tabulate the number of legs and teeth, note food preferences, and characterize habits of reproduction. […] But I’ve never encountered a full description of the two-legged ape. We Homo sapiens, so eager to describe the rest of the world, have been chary about committing our own natural history to paper.
This seems unfortunate. For one thing, it reinforces the notion that we’re not normal animals. It lends the impression that we’re too wonderful to summarize; that although the giraffe can be corralled in paragraphs, the human cannot. That’s unfair to other species. On the flip side, it suggests we’re misfits, as animals go. It lends the impression that we’re not worthy to take our place beside the gemsbok and the gorilla; that we are excluded from the brotherhood of mammals. This is unfair to my species.
It also seems unnecessarily dour. What could be more fun than describing the human, after all?”

From the introduction. The book is quite funny and you learn a lot of new stuff. That said, it also gets a few things wrong, and I’ve gotten a bit annoyed a couple of times because she keeps repeating a common mistake people make when dealing with evolutionary bioloy: Assuming traits or behavioural strategies which are widespread today must necessarily have been advantageous in the past. It’s an easy mistake to make, but it’s the wrong way to think about these things: A general rule of thumb is rather that all it takes for a given trait to persist over time is for the trait to not be so costly as to give rise to a significant evolutionary disadvantage. Traits that impact the number of offspring in a positive way will generally spread (if certain other conditions are met), but neutral traits and adaptions can easily persist over time as well. Harmful traits are the only ones that generally have a hard time making it over time, and if you see the trait in individuals today and it’s been around for a while, the trait probably isn’t all that harmful – at least in terms of offspring impact, likelihood of mating ect.. She makes the mistake both when talking about traits more or less directly linked to genetics (‘color blindness has persisted because: “it gave hunters an advantage in spotting khaki-colored animals in the khaki-colored grasslands of human prehistory”) and also when talking about purely cultural adaptions (according to her, the new HIV study showing that circumcision reduces infection risk (slightly) might indirectly be part of the explanation why people thousands of years ago decided to cut off parts of the penis of their male children and keep doing it – “If circumcision does indeed reduce the risk of males contracting fatal diseases, that could well have kicked “cultural evolution” into gear long, long ago: Those groups of humans who practiced the cultural behavior would enjoy better survival rates.” My response would go somewhere along these lines: Sorry for asking, but what about wound infection risk 2000+ years ago? Risk of botched circumcision reducing number of offspring to 0? And just how big would the impact on transmission rates of i.e. sexually transmitted diseases have to be to actually offset these costs (the effect size in the HIV study was quite small)? Also, lots of fatal diseases one might come up with, including quite a few sexually transmitted ones, aren’t even impacting fitness to any significant degree despite the fact that they’re deadly (which is part of why there are so many of them still around) – if you die at the age of 35, after having had 10 kids, for all practical purposes the disease doesn’t really matter all that much in the big picture. To me, the interesting question is not how a cultural adaption like circumcision might have provided the group with an evolutionary advantage, but rather why it was not so disadvantageous to the group as to go out of style completely over time). In her book she’s finding ‘evolutionary explanations’ all over the place also in places where it seems rather obvious to me that really none need even exist – these are not the only examples.

Aside from this, it’s really quite good, interesting and fun – there’s lots of good stuff as well. I’ll post more on the book later on.


September 29, 2011 - Posted by | Anthropology, Biology, Books, Evolutionary biology, Genetics

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