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Even men's sperm like to cheat

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THE well-known connection between human sexuality and storks may be dubious, but there is a lot to be learned from our closer relatives like monkeys, gorillas and lemurs.

Robert Martin, curator of biological anthropology at Chicago's Field Museum, has dedicated a 50-year career to primate behaviour, ecology and evolution.

His own work is mixed with that of many others, from Thomas Malthus to present, to create a fact-filled tour of the reproductive process from sperms and eggs through to baby care and weaning.

A major theme throughout all the chapters is determining what is "natural," with the evidence coming from early human societies and comparisons with other primates.

For example, it turns out that differences between sperm, including the relative strength of their tails, is related to the mating habits of each species.

Primates that have evolved to be monogamous have a certain shape of sperm, while promiscuous species have a different shape. Human males, sad to say, do not have monogamous sperm.

The book poses a wide range of questions and offers many answers, without shying away from controversy. Regarding nursing habits, he confirms that breast-feeding has a clear advantage over bottle-feeding.

Regarding the rhythm method of birth control, it's not very effective and may even lead to a higher risk of birth defects.

Some of the material is simply interesting, like the differences in mothering habits between mammal species. Some mammal mothers have large litters of nearly helpless infants and offer minimal care beyond their milk. Others have just one or two well-developed offspring and care for them closely.

We humans suffer some disadvantages of both -- single offspring and long pregnancies, but our infants are still helpless compared to other higher primates. At some point, however, many years ago, women lost their back hair and babies lost their ability to hold on for themselves.

In a scientific "win" for the Bible, it turns out that the reason that human childbirth is so painful really is because of our appetite for the fruit of the tree of knowledge -- our big heads holding those big brains. If it weren't for that narrow birth canal, our heads could be even bigger (and pregnancy could be even longer).

For a book devoted from cover to cover to sex, it is far more scientific than sexy. By the end, one might be utterly desensitized to the word "copulation" and mental images of the same. On the other hand, Martin's restraint, or modesty, is evident in his near total abstinence from innuendo in the face of constant opportunity.

The book does jump from one topic to another and back and forth across evolutionary time rather abruptly, but the material is almost always compelling.

There are a couple of exceptions, including one chapter that descends into a long discourse about some academic distinction between types of placentas. The reader simply has to lie back and think of England for a few pages.

While some of Martin's conclusions about what is "natural" may be controversial, given how universal the topics of sex and child-rearing are, he is careful to not equate the natural way with the right way.

Studying our evolutionary and more recent past tells us where we came from, and it may offer clues as to why we are shaped and programmed as we are, but the future is still up to us, and our big heads.

Paul Klassen is a Winnipeg engineer.

Republished from the Winnipeg Free Press print edition June 15, 2013 A1

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