Horses and Hooves
Substantiated by vast numbers of fossil bones from North America and Europe, representing different geological strata, T.H. Huxley (grandfather of three very famous Huxleys!) had concluded that the horse had evolved from dog-sized ancestors with 4 fingers on each front and three toes on each back extremity. So, towards the latter quarter of the 19th century he had basically unravelled the palaeontological pedigree of the modern horse.
When asked why the horse evolved into a one-fingered one-toed animal, palaeo-climatologists are quick to point out the climate change that must have caused a spread of dry savannah-types of grasslands. Zoologists then explain that a four-fingered foot may have suited the irregularities of the soft forest floor, but not the uniform open and hard surfaces of a savannah. And yet, the reduction of toes and fingers started some 30 million years prior to the landscape changes and continued long after the climate change had come to a halt. It was the Russian Vladimir Kovalevsky, who tackled this discrepancy. He had actually studied law, but as a 25 year old had already made a name for himself as a palaeontologist and as an enthusiastic supporter of evolution had already translated Charles Darwin’s book “The Variation of Animals and Plants under Domestication”. He also translated two other books by Darwin.
Being well versed in several languages, Kovalesvsky published three significant monographs in three different languages (none of which was his mother tongue) on horses and other ungulates including remarks on hippopotamuses. What makes his work so impressive is that more than 100 years after the appearance of his publications, physiologists have “re-discovered” and learned to appreciate his arguments. Take a tapir, for instance, a forest-dwelling, leaf-browsing animal similar to the horse’s ancestor, but which occurs in Malaysia and South America. A tapir’s feet have 14 toes, four in the front, three in the back. A modern horse has only one on each foot. Kovalevsky argued that each toe has two supplying arteries and veins and the internal friction of the blood flow alone must lead to a considerable loss of energy in the tapir. If we add the risks of blockages, diseases and toe infections, the tapir and thus the prehistoric horse, are further disadvantaged. As long as food is plentiful, however, and opportunities to hide from predators exist (as in the jungle or woods), no real pressure to reduce the number of toes exists. But with dwindling food sources and a switch from a leafy diet to a grassy diet, the principles of economy and energetics demanded toe reductions. The harder terrain of the savannah then becomes secondary. The median toe, which carries most weight with least muscular support was favoured for reasons of mechanics, economics and maximum efficiency.
Not being an osteologist myself, I do find this physiological explanation of an evolutionary phenomenon by someone trained in law thought-provoking and interesting. Perhaps more lawyers should become involved in science – but recognition of their ideas, of course, could take 100 years or more. And what should worry them as well is that poor Vladimir committed suicide at the age of 40.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
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