23 February 2005

What Species is the Best?

Why do we humans think we are the acme of creation? Is it just species ego? What is so special about Homo sapiens?

People say, "We're the only species with high intelligence; the only species with language. And don't we have opposable thumbs?" Big deal.

It is ridiculous to regard humans as the pinnacle of evolution. We are in no sense the "goal" of evolution, the "highest" organisms, or the "most advanced" species.

The Great Chain of Being is Bunk

The "chain of being", also known as the "ladder of perfection", "scale of nature" or "scala naturae", was a concept developed in classical Greek philosophy in the forth and third centuries BCE. Species were believed to be fixed, static, and to be the manifestation of ideal forms or types. These ideas were developed by Plato as the Theory of Forms and by Aristotle as the Theory of Types.

This way of looking at nature was adopted by Christian thinkers and became the basis of medieval European natural philosophy. Even Carolus Linnaeus, when he developed his "Natural System" of classification, based it on the idea of immutable, distinct species "types".

Here is how the Chain of Being was illustrated in 1579. Rocks are below, and God above. Humans are between animals and angels.
1579 drawing of the great chain of being from Didacus Valades, Rhetorica Christiana from http://en.wikipedia.org/wiki/Great_Chain_of_Being
The Scala Naturae was conceived of as a linear series of "types", from the "lowest" to the "highest". It became embedded in medieval thought and is still part of a traditional way of looking at the natural world. It survives as the concept of a "ladder of evolution" from lower organisms to higher.

One of my favorite uses of the concept of an "evolutionary ladder" is this illustration from Punch. (Remember that Darwin, here represented as the peak of evolution, had written a book about the biology of earthworms.) (You can access the image it here.)

Today the concept appears often as "humor". One of the cleverest uses of this cliche is this beer ad.

These ideas were extended during the era of European exploration and colonialism to rank "races" of people from backward to advanced. Western Europeans saw themselves as the peak of perfection, of course, and ranked other "races" below themselves.

The idea of a fixed chain of being, reflecting God's will, faded during the 19th century. It was completely incompatible with Darwin and Wallace's theory of origin of species by natural selection.

Over the past century and a half there has been a paradigm shift from trying to see how nature fits into a fixed, divinely ordained structure to understanding that species, ecological communities, and even organisms are dynamic and impermanent.

Aren't we "higher" organisms?

Images of a hierarchy of perfection are still with us, and strongly influence the thought of non-scientists. Even scientists sometimes catch themselves calling some organisms "primitive" or "lower" and others "advanced" or "higher". In particular, we should be very careful not to confuse "simple" with "primitive".

In biology "primitive" should just mean "resembling ancestors", and "advanced" or "derived" means "with features not found in ancestors".

There is no reason, except Chauvinism, to think of human beings as "more advanced" than hummingbirds, brachiopods, or octopi. Each is the result of successful adaptation to a particular ecological niche, a way of making a living and leaving offspring.

We tend to overvalue "intelligence" because it is our salient adaptation. But to quote the late, great evolutionary thinker Ernst Mayer (from a discussion of the chances of finding extraterrestrial intelligence),
Adaptations that are favored by selection, such as eyes or bioluminescence, originate in evolution scores of times independently. High intelligence has originated only once, in human beings. I can think of only two possible reasons for this rarity. One is that high intelligence is not at all favored by natural selection, contrary to what we would expect. In fact, all the other kinds of living organisms, millions of species, get along fine without high intelligence.

The other possible reason for the rarity of intelligence is that it is extraordinarily difficult to acquire. Some grade of intelligence is found only among warm-blooded animals (birds and mammals), not surprisingly so because brains have extremely high energy requirements. But it is still a very big step from "some intelligence" to "high intelligence."

The hominid lineage separated from the chimpanzee lineage about 5 million years ago, but the big brain of modern man was acquired less than 300,000 years ago. As one scientist has suggested (Stanley 1992), it required complete emancipation from arboreal life to make the arms of the mothers available to carry the helpless babies during the final stages of brain growth. Thus, a large brain, permitting high intelligence, developed in less than the last 6 percent of the life on the hominid line. It seems that it requires a complex combination of rare, favorable circumstances to produce high intelligence (Mayr 1994).
We give ourselves lots of points for intelligence, but if we were to rank species by any other feature we would be nowhere near the "top". The point is that we shouldn't rank species at all.

Sure, the giant sequoia is the biggest (or maybe an Armillaria is).) The falcon is the fastest, strain 121 the hottest, Prochlorococcus the most abundant (we always want to know the extremes), but every species has won a battle to survive, each in its own way.
Prochlorococcus is the smallest known phototrophic bacterium. It is probably the most abundant organism on earth. It may be responsible for 30-80% of the primary production (fixation of carbon using energy from the sun). It produced more of the oxygen you are breathing right now than any other organism. It was not discovered until the late 1980s. More here.
Biologists, probably more than anyone else, are in awe of the incredible adaptations of every organism to make a living and leave progeny. The more you study, the more sublime wonders you see.

further reading:
Wikipedia article
Dictionary of the History of Ideas
Evolution Education Wiki

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