Tag Archives: animals

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

The Minds of Dogs and How Pointing Evolved

Recent research sug­gests that domest­ic dogs seem cap­able of dis­play­ing a rudi­ment­ary “the­ory of mind” — 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 you’re too insec­ure in your own sexu­al­ity, just pic­ture Adam’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 […] 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.