Questão 18 - UNIMONTES 2° Etapa 2016

            Our weird lack of hair may be the key to our success

 

[1]   Look closely at your friends, family and even strangers. Spot anything strange?

  Ignore any large noses or unusually-shaped brows. Instead, look at their hair – or rather, the lack of it.

  It might not seem strange, because we are used to having relatively little hair covering our bodies. But

when we compare ourselves to the rest of the mammals, and our closest living ape cousins, it is downright

[5] bizarre that we are the only large-bodied mammal with so little of it.

  Unlike hairy chimpanzees and bonobos – and all other primates – most of our skin is on display. We

have evolved this way, even though fur is beneficial: it insulates and protects the skin, and in some cases

acts as a useful camouflage. So if it is so advantageous, why did we lose so much of it?

  It was Charles Darwin who first taught the public that humans are descended from an ape-like

[10] ancestor. He also wondered why we had so little hair.

  “No one supposes that the nakedness of the skin is any direct advantage to man; his body, therefore,

cannot have been divested of hair through natural selection,” Darwin wrote in The Descent of Man.

  He proposed that we lost much of our fur due to sexual selection: we preferred hairless mates, and that

is why hairlessness became common.

[15]   But that cannot be the whole picture. Before a preference

for hairlessness began, we first had to start losing hair.

  Our earliest human-like ancestors, known as hominins, were

ape-like. For them, fur would have been useful, keeping them

warm on cold nights.

[20]   Something must have created an evolutionary pressure for

these hominins to lose their fur.

  A few million years ago, there were several hominin species

roaming the Earth. These included the famous fossil known as “Lucy”, an Australopithecus afarensis from

3.2 million years ago.

[25]   These hominins were ape-like. Lucy was a lot like a chimpanzee, except that she could walk upright

and had a slightly bigger brain. Her skin was not preserved, but she was probably covered with fur.

  However, between two and three millions years ago our ancestors began to inhabit more open

savannahs. This meant they were out in the Sun’s glaring heat for many more hours each day.

  Around the same time, they also started to hunt and eat more meat – and game animals were more

[30] abundant in the open. This move into open spaces offered an explanation for our lack of hair.

  In the 1990s, Peter Wheeler of Liverpool John Moores University in the UK came up with a

mathematical model showing how much excess heat hominins would need to lose in open habitats in order

to function. If their brains got too hot, their thought processes would be impaired.

  If the hominins were covered in hair, they could not have lost heat fast enough. Wheeler reasoned that

[35] two related changes happened that allowed our ancestors to keep cool.

  One was an upright gait. Walking on two legs meant that only the tops of their bodies were under

direct sunlight.

  But the hominins also started running long distances. This meant they could bring down large game

animals by running them to exhaustion, but it also put them at risk of over-heating. To cope with that, they

[40] needed to lose their fur – in order to help them sweat. [...]

Fonte: HOGENBOOM, Melissa. Our weird lack of hair may be the key to our sucess. 2 ago. 2016. Disponível em: http://www.bbc.com/earth/story/20160801-our-weird-lack-of-hair-may-be-the-key-to-our-sucess. Acesso em: 15 set. 2016. Adaptado.

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