Peter Andrews is an Irish science journalist and writer, based in London. He has a background in the life sciences, and graduated from the University of Glasgow with a degree in Genetics

Male preference for women’s permanently swollen globular breasts is somewhat anomalous, but to date, no widely accepted evolutionary explanation has been offered. What is the latest in this titillating area of research?

Science has always been concerned with the big questions. How did we get here? How did the universe begin? What is the nature of reality? And now, the scientific method has turned its dispassionate gaze towards that eternal and pressing question: Why do men like women’s breasts?

‘’Because they do’’ or ‘’because they’re nice’’ are not acceptable answers here. Neither, for that matter, is ‘’because media portrayals brainwash them into liking breasts’’ (if you believe this, have a conversation with any straight man). In science we must seek always to be disinterested and unbiased, and to apply the principles of discovery as rigorously as we can. That is how a recent column in Psychology Today by Robert D. Martin, a distinguished anthropologist, treated this topic. So let us examine the evidence, and please, let us have no giggling or smart comments from the back of the room.

Breastology

Although the reason for breasts’ existence is obviously breast-feeding, women’s capacity for milk production is not associated with breast size (at least not before pregnancy). Furthermore, there has been no clear association between hormone levels and breast size. So why have men evolved to like them?

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An early hypothesis was that breasts are an honest signal of fat reserves, which would come in handy during lean times for our hunter-gatherer ancestors. If that were true, however, men should find breasts no more erotic than fat elsewhere on the body. Chalk that one off.

One of the most popular theories has to do with pair-bonding. Neurology studies have proven that women are flooded with oxytocin, the bonding hormone, when their nipples are stimulated by a nursing baby, or indeed by a sexual partner. So, men who pay extra attention to this will impress their mate, and make it more likely that she will have his babies. Make of this theory what you will – it seems to suggest an unlikely degree of unselfishness in men – but there may be something to the bonding aspect.

Switching positions

One person who thinks bonding plays a part is British anthropologist Edward Dutton; he has suggested that breasts evolved to resemble buttocks. Seeing as our distant ancestors mated from behind, like our primate cousins, at some point they must have switched to face-to-face. This moment in evolutionary history was hugely important, because with front-facing intercourse came sustained and intense eye-contact theretofore absent from the act of procreation.

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Much has been speculated about the profound anthropological changes face-to-face sex may have brought on the human species, not least the new depths of pair-bonding it must have triggered. Dutton thinks that one of the byproducts of the change may have been that female breasts expanded so as to create a cleavage reminiscent of the previously all-important backside.

How old are you?

Possibly the most intriguing argument is that of evolutionary psychologist Frank Marlowe. His ‘nubility hypothesis’ proposes that full, pert breasts are an honest signal of youth, and therefore fertility. In the ancestral environment, humans often went without clothing on their torsos, meaning the females’ breasts would have been more on show. Before birth records and possibly even before the advent of language, there was no way to know the age of other adult humans, except by visual physiological signals.

As women age their breasts begin to sag due to the pull of gravity. Therefore, fleshy lumps on females’ chests became one fool-proof way for males to know the rough age of females, even if it was subconscious. Over aeons of time and thousands of generations, those men with an internal urge to mate with women with younger breasts would on average have had greater reproductive success, seeing as they were mating with younger (but adult) women.

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Once a preference for a certain kind of breast kicked in, sexual selection may have also entered the picture. Women having the types of breasts men prefer also had the most reproductive success, leading to a feedback loop of selection for the permanently swollen breasts we see in Homo sapiens, somewhat unlike any other mammal species.

Fast forward millions of years, and attraction to breasts is a near ubiquitous trait among heterosexual men (and homosexual women).

It’s a good story, but does that make it true? And do the cultural elements have any role to play at all or is it all just cold hard evolutionary biology? And if natural selection is still at work, what kind of breasts will the man of the future find attractive - if any at all?

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