When one sex is different to the other,
this is known as "sexual dimorphism".
Seals spend much of the year swimming
through the seas fishing as they go, while they may spend time with
other seals, they do not form strong bonds with a partner to rear their
When born, the young are fed only
on milk by the mother and soon learn to fish for themselves. Birthing
usually takes place on a beach with many other seals and the female
comes into oestrous (i.e. is ready to mate again) shortly after giving
Because of this life-style, many seals
have evolved a strong sexual dimorphism. The males arrive on the birthing
beaches often before the females and fight to establish and defend their
territories. The most successful male, often known as the "beachmaster"
gets to mate with as many as a hundred females that are in his territory.
Therefore there is a great advantage
to being big and strong, and if a male is not among the biggest and
strongest, he will not get to mate at all. This has led to a pronounced
sexual dimorphism. (difference in size and/or appearance between the
Photo; © Paul Ward - Pentax equipment,
100mm lens, 35mm film, K64.
This picture may not be copied or
used in any manner without prior written permission.