The Biology of Twinning in Man

Twins are probably by no means unknown to most people - for instance in the sporting world of my Australian homeland there are quite a number of cases of note - yet very few people understand the biology behind twins. Although this book suffers a good deal from its age - people like Tim Flannery, Tom McMahon, John Rushton, and Michael Laker clearly give evidence that there is something much more "designed" than randomness involved in dizygotic twin frequencies around the world - if you want a basic introduction to the facts about twinning in humans you will get it here without any doubt. Bulmer deals with every aspects of twinning from the frequency of twinning in humans to the liabilities mothers of twins face vis-à-vis those of single children. He also goes into less common detail about the extreme difficulties of higher order multiple births - and provides little-known but easily understandable details about their frequency. Bulmer shows that for most of human history mothers of twins were at huge disadvantages both in terms of their much greater health risks and the low birth mass and short gestation of their children. For this reason, Bulmer shows that only when major health improvements were made could twins compete with singleton children, and he shows this had and has major consequences culturally. Another very interesting sidelight is Bulmer's look at how single birthing evolved as the most productive strategy in humans and other primates (except for the primitive tree shrews). Bulmer compares this with the situation in animals that typically give birth to multiple young. He should, however, have looked at the environmental conditions that encourage singleton births and compare with those animals that give birth to multiple, highly precocial offspring. All in all, though it is certainly dated, "Biology of Twinning in Man" is a simple and useful overview of what most people should know about multiple births in humans.