Well-developed brain

Source: scientias.nl
Of all new-born mammals, the baby Weddell seal has the most developed brain. This fact is of great importance given the dangerous environment in which they live. This well-developed brain, however, comes at a price.
The brain mass of twelve Weddell seals was studied: ten new-born pups and two adult females. On average, the pups’ brains were found to be 69 per cent as large as those of adults. Supplementary data from another study boosted this to more than 70 per cent, an absolute record for new-born mammals. In comparison: the brain of a new-born human baby has only 25% of the adult human brain’s mass.

Weddell seals truly need that more highly developed brain. They must be able to orient themselves under water right away, and at less than three weeks old they start to dive under the ice. Such a dive is dangerous: if they don’t find their way back out in time, they drown. These seals must develop this capability quickly, as they must live independently very soon — Weddell seal mothers leave them to their own devices from the time they are 40 to 50 days old.

The seal pups’ large and well-developed brain comes at a price: brains cost a good deal of energy in the form of glucose. While nursing the pups, the seals’ mothers have to supply this energy. The mothers rapidly lose body mass, sacrificing their own reserves for the sake of their young’s survival and growth.