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 anatomyÂ andÂ why animals are the way they are.
A perfect take on the topic isÂ J. B. S. Haldane‘s 1928 On Being the Right Size. In this absorbing short essay, Haldane looks atÂ why rhinos have short, thick legs; why theÂ 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 waterâ€”that is to say, gets wetâ€”it is likely to remain so until it drowns. [â€¦]
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
Recent research suggests that domestic dogs seem capable of displaying a rudimentary “theory of mind” â€” a very human characteristic whereby you are able to attribute mental states to others that do not necessarily coincide with your own (in a nutshell). Stray domestic dogs, meanwhile, do not display this trait, suggesting that such mental attributes are developed through close contact with humans. That’s interesting, but not the main reason I’m sharing this information with you.
This cognitive difference between stray domestic dogs and their housebound brethren was uncovered by testing whether or not they understood the very human action of pointing (y’know, with your index finger). What struck me most in this discussion was this brief theory of how the action of pointing evolved:
Go ahead, let your wrist go limp and look at your hand from the side, or if youâ€™re too insecure in your own sexuality, just picture Adamâ€™s limp wrist at the moment of creation in Michelangelo’s masterpiece on the Sistine Chapel’s ceiling. See how even in this relaxed state the index finger is slightly extended? By contrast, when chimps do this [â€¦] their index finger falls naturally in line with their other fingers. Povinelli and Davis reason that this subtle evolutionary change in the morphology of our hands, which occurred after humans and chimpanzees last shared a common ancestor five million to seven million years ago, is at least partially responsible for the fact that human pointing with the index finger is so culturally ubiquitous today.
The argument goes something like this. When young infants begin reaching for objects just out of their range, adults are most likely to respond to those reaching attempts and to retrieve the item for the baby when the latter’s index finger is more prominently extended. That is to say, initially, the adult mistakenly reads into the child’s reaching attempt as a communicative gesture on the part of the child. Over time, this dynamic between the child and adult serves to further “pull out” the index finger because the child implicitly learns the behavioral association, so that it slowly becomes a genuine pointing gesture.