A quick, decent read.

This is a book about human diseases, particularly genetic diseases, and our adaptations to them, and them to us. We have a lot of diseases that are caused by genetic defenses to other diseases or to the environment, and it’s not generally appreciated how significant the impact this kind of evolution has had on us. The book is well sourced and has a lot of evidence to show that, in addition to the usual, known adaptations like sickle cell anemia to combat malaria, we have a few other fun traits: type 2 diabetes may be related to the cold, and hemochromatosis may be an adaptation to the plague. Good trivia, but nothing new here.

There’s a sparse chapter on human evolution, focusing on the aquatic ape side of things. This seems to be the pet topic of every science writer: it’s all completely unprovable but very interesting to speculate about. I’m bored of it now. Leave it to the professionals!

There’s some very interesting stuff about ‘gene hopping’. We’ve basically got chunks of genes that act like viruses, but affect only ourselves, and there’s good evidence that evolution picks up when an organism lives a stressed life. Which is saying that we’re evolved to evolve when we need to, which seems so obvious to me that it should be self-evidently expected. It’s good to see some evidence of it.

The last fourth of the book, however, was all new to me–epigenetics. Essentially, incredibly small changes can cause organisms–including complex mammals, including us–to permanently disable their own genes by attaching a methyl group to a particular gene. Zygotes–including human zygotes–are turning off genes–permanently–within hours of conception based on the mother’s environment. This is just mind-blowing; we’ve long known genes can be expressed or not, but that the triggers should be so small and sudden is pretty nuts. Fortunately, we don’t know many details yet, and it seems that ‘turning on’ many genes will result in ‘turning off’ many others, so it’s impossible to tell expectant parents what they should do. If you could, with changes this big for such small changes…pregnancy is stressful enough. I’m glad I’m male.