Size and Complexity: Why Animals Are the Way They Are

From bone strength and oxygen absorption in larger animals, to the perils of surface tension and poor eye design in smaller ones: just some ideas to consider when studying comparative anatomy and why animals are the way they are.

A perfect take on the topic is J. B. S. Haldane‘s 1928 On Being the Right Size. In this absorbing short essay, Haldane looks at why rhinos have short, thick legs; why the smallest mammal in Spitzbergen is the fox; and, primarily, how the size of an animal determines almost everything about its anatomy.

There is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. A man coming out of a bath carries with him a film of water of about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight of water. A wet fly has to lift many times its own weight and, as everyone knows, a fly once wetted by water or any other liquid is in a very serious position indeed. An insect going for a drink is in as great danger as a man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water—that is to say, gets wet—it is likely to remain so until it drowns. […]

The higher animals are not larger than the lower because they are more complicated. They are more complicated because they are larger. Just the same is true of plants.

As is typical of Haldane, he finishes with something a bit more political than anatomical, stating that “just as there is a best size for every animal, so the same is true for every human institution”. Something to consider.

via The Browser