Tuesday, December 3, 2013

Brain and the Birth Canal

In human beings, giving birth is a difficult and risky job. No other animal faces such difficulties while delivering babies. Why should it be so?
Sometime during our journey of becoming human from apes, our ancestors became upright and began walking on two legs. This happened 20 lac years ago, or may be even earlier.
One effect of the upright position was that the birth canal became narrow. Giving birth became an ordeal that women go through till today.
At the same time, the human brain was becoming larger. The large size of the brain is one of the things that makes us human. Our brain is around 1.4 Kg, 2% of our body weight. Elephant’s brain is 5 Kg, only 0.08 % of its weight.
So it was a double challenge. The birth canal became narrow and brain became large. In order to make birth possible, the brain of a baby is only 28% of in size at birth. But it is still too large for the narrow canal. Then evolution came up with another trick.
The head of a baby is not one solid ball like us adults. It is made up of five separate parts, joined by soft patches. Search Fontanelle on internet and you can see what it is. The Fotanelle serves two purposes:
- At birth, the head is pressed together so that it can pass through the birth canal.
- After birth, the brain grows rapidly. The Fontanelle allow this growth. One fotanelle closes a few weeks after birth, another sometime after the first birthday of the baby.
The twin challenge of large brain and small canal has another interesting effect- family and societies. The baby’s brain is not complete at birth. So it needs a long time to learn even basic things like eating. To ensure training of the babies, long term bonds like marriage evolved. Family became a very important unit in human culture, owing to a large brain and small birth canal.

No comments:

Post a Comment