Why a sudden menopause?

Why do we — and the dolphins or orca — usually have sudden well-defined menopauses in mid-life while all other animal species do not? In other animals, fertility only fades away gradually with advancing age in the same way as youthful strength and vigour.

Ah, but how do we know that it’s sudden in dolphins? After all, with dolphins spending almost all their time under water, and only momentarily leaping above water — and only then when they are keenly interested to observe us on our boats — or are they showing off? — it is surely impossible to know.

The realisation came only recently to a long-term scientific project studying a pod of orca — of about 80 individuals — in the Pacific not far from the shore in California. After 50 years of observations — during which they knew the history of every individual — the researchers were able to confirm a suspicion they’d had fro many years. At around the age of 40 a female dolphin had either recently given birth or she had stopped giving birth altogether. There was no half-way house — it was just like us.

The reason for the sudden change was clearly shown by the fact that the females continued to lead an undiminished strenuous life afterwards. If anything, they take to keeping the more exuberant adolescent males in line and need to be even more energetic.. They also act as midwives to young females.

More than anything else, the older females lead others in their pod to feeding grounds, particularly when times were difficult and past experience is at a premium. Youn males, even when they have families of their own sometimes return to swim closely with their mother as though to absorb her skills and knowledge.

In short, post=menopausal females were absolutely necessary for the survival of their pod. If their usual source of food failed them then one or two of the very old females might remember techniques they had seen other pods using in different regions of the ocean.

Like early man, pods with entirely different cultures and call-signs in different parts of the world, could only survive by making one particular hunting method into a fine art, sometimes eating fish as small as anchovies, sometimes by attacking creatures larger than themselves.

This razor-edge existence on one oceanic region or another requiring different skills is very similar indeed as early man’s, both having to diversify in order for the species to survive as a whole. The story of the dolphins suggests very strongly that the human menopause evolved in the way that it did for the same reason as in the orca.

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