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Why Are Human Breasts So Big?

Why Are Human Breasts So Big?

(bright music) – [Narrator] Breasts come in
different shapes and sizes, but there’s one thing
they all have in common. They are unique to humans. More than 5,000 mammalian
species inhabit this planet, yet homo sapiens are the only life forms with permanent breasts. Some may call this human anomaly sexy, but it also begs the question, why are human breasts so big, and were they an evolutionary mistake? (text clicking) Every other mammal
develops temporary breasts during ovulation and, or nursing. Basically their purpose
is to produce milk, so once the milk is gone,
the breasts disappear. But this isn’t the case for female humans whose breasts form during
puberty, not pregnancy. So at some point in our
evolution, something changed. But what? For example, in 1987,
biologist Tim Caro explored seven existing theories on this subject. One was that breasts allowed mothers to nurse newborns from their hip, giving them more mobility to multitask. But it doesn’t explain
why breasts stick around after the nursing stage is over. Perhaps the most popular
idea was first proposed by Charles Darwin and later
explored by zoologist, Desmond Morris, in his
1967 book, The Naked Ape. In it, Morris suggests
that breasts evolved as a sex symbol, to replace
the swelling rear end of other female primates during ovulation. Once our ancestors
starting walking upright, the sexual organs were no
longer as obvious to spot, so males had no way of knowing when a female was sexually mature, and breasts may have formed as a result. This theory would at least explain why women’s chests swell during puberty, but it still can’t explain why they stick around after menopause. Let’s take a closer look
at the human breast. The big difference is
that it contains more fat than other female mammals. The fat fills out the breast tissue, giving it shape, sort of
like milk, but permanent. Human breasts can become so large it can cause back and chest pain. This is why many women
get breast reductions. More than 61,000 received
a breast reduction in 2016, in the US alone. But breasts aren’t only
uncomfortable for some, they can also be deadly. Breast cancer is the number one cause of cancer related deaths
in women, world wide. It effects roughly one and a
half million women each year and it killed 570,000 of them in 2015. Yet as far as scientists can tell, breast cancer is not common
among other primates. This could be because the risk
of cancer increases with age, and other primates don’t live long enough to develop breast cancer, or perhaps, it could have something to do with the permanent breast tissue itself. – [Dr. Callahan] Cancer is more common in rapidly dividing tissue. Every time cells are born and die, there is an opportunity
within the cell cycle to make mistakes in repairing DNA and essentially, a cell with mistakes can become a cancerous cell. Breast tissue divides at a rapid pace, so there’s a greater
opportunity to make mistakes. – [Narrator] That may explain
why removing both breasts reduces a woman’s risk
of breast cancer by 95%. Of course breasts have
established their place in human culture and society. They can make women feel
wanted, liberated, or empowered. And they’ve helped build entire empires based simply on their power to attract. It looks like, for better or worse, human breasts are here to stay. (bright music)

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