Freaks of Nature, Mark S. Blumberg
The title put me off this right away, the opening chapter helped somewhat because it promised to be more than a parade of curiosities, showing some sympathy and understanding, but ultimately I didn’t feel it did really manage to rise above that. There was a lot of reiteration about ‘circus freaks’, etc, and I don’t think it got past the novelty factor of such cases. There were some rather odd assertions — that the figure of Atlas could’ve been inspired by people with a developmental issue who ended up with a globe of brain matter sticking out from their shoulders, for example; it seems a rather ridiculous idea to me, and I couldn’t find anyone else saying the same thing. And saying Janus could’ve been inspired by cases where faces appear on both sides of the skull — maybe, but I think it more likely it’s a metaphorical depiction arising from what the god was said to do.
The science wasn’t particularly in depth or surprising. I don’t think anyone denies that developmental factors can be as important as genetics during gestation.