Joined: May 2002
Another bit on wheels:
Some thoughtful points provided by Dawkins, but it should be pointed out that other macro-scale features like horns and armor don't require vessels or nerves. Dawkins asks this question for the macro-scale wheel:
"But what would the evolutionary intermediates have looked like?"
The same question remains in play for the micro-wheel.
Just to be picky, antlers at least (e.g. deer antlers) do require blood vessels to grow (deer scratch off the velvet before breeding season and then the horns fall off). Other forms of armor etc. I'm not so sure, it depends if they are derived from hair or bones or what.
But yes, it's the intermediates that are the key. The twisting blood vessels seem to be impossible to gradually convert into vessels with rotary joints.
As for whether car-style wheels, if intelligently designed into a critter, would even be favored vs. legs, I'm not so sure. The african savanna and similar plains areas seem like the most likely places (salt flats and beaches etc. are pretty restricted environments).
That appears to be the primary conclusion of LaBarbera, who actually got an article out of this bit of speculation we're doing:
“It was one of those curiosity questions that you get asked after a lecture that has nothing to do with the lecture,” LaBarbera said. The student came up and asked, “Why don’t animals have wheels?”
LaBarbera gave the stock answer. Animals with wheels would have to evolve a circulatory system that could pump fluids through a rotating joint, an unlikely though not impossible development. But LaBarbera further wondered if wheels would really help an organism. The answer is no.
“Wheels are useful on manmade, artificial terrain like streets and parking lots, but they’re not terribly useful on natural terrain,” LaBarbera said. “If you put on a pair of Rollerblades, you can go like crazy down the sidewalk, across the street and around the parking lot, but don’t try it on the grass. It doesn’t work.”
LaBarbera also asked himself in what natural environments would wheels actually be useful? It turned out that rolling forms of locomotion––the equivalents of wheels––have evolved in those environments where the vegetation is sparse and the landscape is relatively flat. On the African savanna, for example, dung beetles make little balls out of elephant dung, which they use to feed their larvae.
“The student forced me to think about the question in a different way than I ever had and indeed than anyone had ever thought about it,” he said. “The real answer turned out to be a lot richer, I think, than the standard answer.”
And the American Naturalist article that the question inspired continues to be LaBarbera’s most frequently requested reprint.
The article is online in JSTOR if you have access:
Why the Wheels Won't Go
American Naturalist, Vol. 121, No. 3. (Mar., 1983), pp. 395-408.
The scarcity of rotating systems in nature is a function primarily of the limited utility of such systems in natural environments; constraints intrinsic to biological systems (such as physiological problems of nutrient supply) are of secondary importance. In aquatic environments, rotating systems are advantageous only at low Reynolds numbers; in terrestrial environments, rotating systems are feasible as a form of transportation only on relatively flat, open terrain and become less useful as the size of the rotating element decreases. Prokaryotic flagella are popularly believed to be the only rotating system in nature, but dung beetles and tumbleweeds also use such systems for transportation. Whenever rotating systems are a feasible mode of transportation, organisms have evolved that use these systems.