From John Hall
Could it be that the intermittent beaching of cetaceans represents the rump of a former shoreline mammal’s urge to return to dry land to breed?
Marine mammals like seals manage their breeding migrations without hazard, although the bulkier sea lions are approaching the limits of their terrestrial mobility. Cetaceans, having reached the more advanced evolutionary stage of turning their backs on dry land completely, may nevertheless experience a residual instinct to return to it, as they did when they were at the half-committed stage represented by seals. They forget that they have grown to a size, and developed a musculature, which works wonderfully when supported by water, but represents a mortal handicap above the tideline.
The deaths of individuals that yield to this instinct will in due course wipe it out, since fewer and fewer beachers will pass on their genes. When we see a beached whale, we are witnessing natural selection at work.
Having started as fish, evolved into land mammals, and returned to their original element, cetaceans will not be able to change their minds again. Dollo’s law, which says characteristics abandoned in the course of evolution cannot be regained, means that when the last beachers have died out, the surviving whales and dolphins will never again experience an urge to leave the water.
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Hadleigh, Suffolk, UK
