Control sex for humanity's future

• Book information
• How We Do It by Robert Martin
• Published by: Basic Books
• Price: ?17.99/$27.99

The purpose of sex was discovered in the 1760s, using dressed-up frogs (Image: Victoria & Albert Museum, London, UK / The Bridgeman Art Library)

The way we reproduce may have unexpected consequences for the future of humanity, suggests anthropologist Robert Martin in How We Do It

IN THE 1760s, an Italian priest called Lazzaro Spallanzani discovered the purpose of sex by dressing male frogs in taffeta pants. When the frogs were clothed, eggs laid by females didn't grow. Only if the pants were unlaced, releasing the slimy semen inside, did the eggs develop into tadpoles.

Given that many people still believed in spontaneous generation of living creatures from inanimate matter, Spallanzani's experiments were breakthrough science: his dressed-up frogs guided developments in everything from barrier contraception to in vitro fertilisation.

The more we know about the nature of reproduction, the more we can control it, just as Spallanzani did. By doing so we can also control our own future, suggests biological anthropologist Robert Martin in How We Do It, his ambitious survey of reproductive science. In a couple of hundred pages he covers 1.5 billion years of sex, encompassing the sexual evolution of microorganisms, mating practices, development of the human brain, and even cultural differences in breastfeeding. All of this is intended "to provide much-needed context" for our reproductive behaviour today, Martin writes. "Successful breeding is the key to evolution."

Martin is at his best when he addresses this goal, providing context in the form of detailed biological descriptions, along with the perils of misinformed decisions. He argues that some of the most counterproductive strategies have been advanced by the Catholic Church, whose official policy on birth control is the "rhythm method", in which intercourse is timed to avoid the monthly period of ovulation. The technique is notoriously difficult to follow, and so unreliable, according to Martin, that the annual failure rate may be as high as 25 per cent.

Part of the reason for this is a mismatch between the theory behind the rhythm method and reproductive biology: sperm can be temporarily immobilised in deep crypts of the womb, where they can remain viable for many days. Martin foresees a problem if one of those timeworn sperm eventually fertilises an egg: the chromosomes may no longer be in optimal shape. He goes on to postulate provocatively that this may be the cause of birth defects, including the above-average incidence of Down's syndrome in Roman Catholic families.

But religion is not the only domain that should be more attentive to biology. Science also has blind spots, Martin says, especially with respect to treating infertility. For instance, IVF has a statistically higher instance of birth defects than natural pregnancy.

The deeper question is what effect such procedures will have on human evolution, as natural selection is increasingly subjected to new technologies. Here Martin has little to say, beyond his cursory nod to the importance of successful breeding in the opening pages. Indeed, the vast majority of the book is comprised of information in need of insight. Dry writing, combined with a general aversion to expressing opinions, makes for a tome without a clear purpose.

Nevertheless a reader with sufficient determination can infer a lot from the facts. For example, Martin notes that the shape of a woman's pelvis has placed a limit on the size of the brain at birth. So might we expect an effect on human intelligence as caesarean sections become more prevalent?

We need to be addressing these questions. Though disappointingly limited, Martin's book at least offers an opening.

This article appeared in print under the headline "A billion years of sex"

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