The shape of women鈥檚 breasts may have evolved to reduce the risk of mothers smothering their infants while they are feeding, suggests a British researcher.
鈥淧artly because of the obsession with breasts as a sex object, there are big, big gaps in our knowledge of how they actually work,鈥� says Gillian Bentley, a biological anthropologist at University College London.
Evolutionary biologists have long speculated on the reason for the shape of the human breast. Compared to the breasts of other primates, they are unusually large. Mothers among our close relatives, such as chimpanzees and bonobos, are all but flat-chested.
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Because breasts don鈥檛 develop until puberty, biologists have suggested that they help the female attract a mate and keep him interested in her welfare and that of her children. Those with larger breasts were more successful, the theory goes, and produced more offspring.
But that explanation didn鈥檛 ring true for Bentley. For one thing, she points out that the fascination with breasts is hardly universal. 鈥淎mong many cultures where the breast is uncovered it isn鈥檛 such a source of erotic imagery,鈥� she says.
The alternative explanation came to Bentley while she was feeding her daughter. Bentley looked down and realised that if her breast didn鈥檛 protrude, her daughter鈥檚 nose would be buried in flesh while she was trying to suckle. She would be in danger of being smothered. Could the breast have evolved and enlarged precisely to give infants room to breathe?
Most primate infants aren鈥檛 at risk of suffocation, she realised, because they have a protruding jaw and lips. So she suggests that the breast co-evolved with human facial features.
As the face became flatter, the breast became larger to compensate. 鈥淚f infants were dying, that would have provided a very strong selection,鈥� she says.