The cost of massive brains

As we all know,humans have extraordinarily large brains compared to other animals.Mammals weighing sixty kilograms have an average size of 200 cubic centimetres.The earliest men and women,2.5 milion years ago,had brains of about 600 cubic centimestres.Modern Sapiens sport a brain averaging 1,200 to 1,400 cubic centimetres.

We all know that the larger brain is the reason why we have high intelligence.But why are we,human,have such large brains.Why can't there be other animals,like cats,have large brains like us,which makes them can do calculus like us too?

The fact is that a jumbo brain is a jumbo drain on the body.It's not easy to carry around,especially when encased inside a massive skull.It's even harder to fuel.In Homo sapiens,the brain takes about 2-3 per cent of total body weight,but it consumes 25 percent of the body's energy.While the brains of other apes require only 8 percent of the body.

Thus,we huam paid a lot for the large brains we have.

Firstly,we spent more time in search of food which reduced the time we could spend on other things.

Secondly,our muscles atrophied since large amount of energy has been diverted from biceps to neurons which put huam at a disadvantage when competing with other animals.A chimpanzee can't win an argument with a Homo sapiens,but they can rip the man apart like a rag dool.

The reason our big brains pay off nicely is because of the advanced tools like cars and guns that enable us to move faster and attack other animals from a safe distance.But these kind of tools apear in resent times.Before that,human neural networks kept growing and growing,but apart from sharp weapons.During this time,what drove forward the evolution of the massive human brain?We don't know it yet.

Our back and necks paid a lot for the lofty vision and industrious hands.Because of some reasons we,human started to walk upright on two legs.Some scientists argued that it because that walking on two legs saves energy while others argued that it's because of the the environment.Standing up enables us scan the environment easier and free our arms to do more things,like making weapons.However,walking upright has its down sied.It's not easy to supporting an extra-large cranium when standing.Our back and necks suffer a lot when carrying such a brain.

Women paid extra.An upright gait required narrower hips,constricting the birth canal when babies' heads were getting bigger and bigger.Narural selection consequently favoured earlier births.And compared to other animals,humans are born prematurely,as many of their vital systems are still underdeveloped.Human babies are helpless,dependent for many years on their elders for sustenance,protection and education.