Stuff like this drives me crazy:

BUENOS AIRES (AFP) – Scientists have found fossil remains of an omnivorous dinosaur in Argentina -- a missing link to the carnivores, a resear
cher said Monday. "It is an omnivore -- in other words it ate everything (plants and meat) -- which is the missing link between carnivorous dinosaurs and giant four-footed herbivores," said Oscar Alcober, also director of the Natural Sciences Museum in San Juan, 1,200 kilometers (745 miles) west of Buenos Aires. "This is a very important piece of the puzzle on the origin of dinosaurs," said Alcober.

Well, with all apologies to Dr. Alcober, while it may well be important---it's certainly fascinating---it is almost certainly not a 'missing link' in the sense the general public recognizes. The term 'missing link' is almost useless to science these days, and really almost the moment it was first proposed. It's not a term that the paleontologists typically use themselves. The actual PLoS article (summarized on-line here) of Martinez and Alcober referenced in the news item is entitled "A Basal Sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early Evolution of Sauropodomorpha." Do you see anything in there about a 'missing link'? No? Well, what are the conclusions made by Martinez and Alcober? They write:

"We regard Panphagia as the most basal sauropodomorph, which shares the following apomorphies with Saturnalia and more derived sauropodomorphs: basally constricted crowns; lanceolate crowns; teeth of the anterior quarter of the dentary higher than the others; and short posterolateral flange of distal tibia. The presence of Panphagia at the base of the early Carnian Ischigualasto Formation suggests an earlier origin of Sauropodomorpha during the Middle Triassic."

Well, gosh, that conclusion just reeks of 'missing links', doesn't it? In fact, if we compare the rather breathless claim of Alcomber cited in the Yahoo! Science News above, with the rather tightly-focused conclusion from PLoS, we might well get the impression they aren't talking about the same thing at all? What, a layperson might wonder, is the source of all this double talk?

Well, the primary source of this confusion is the radical con
ceptual disconnect between the actual science of evolution and the popular (mis)conception of evolution. Biologists visualize evolution as a process by which populations acquire adaptations in response to local environmental change. Individuals don't evolve, populations do, and what constitutes fitness is typically situation-dependent. Evolution doesn't make creatures that are more 'fit' in some cosmic sense than those creatures that went on. Therefore, our ancestors are not necessarily any more primitive or any less well-adapted to their past environment than we are adapted for the world we live in today. We are not necessarily an improvement, and we certainly can't regard ourselves as the object of evolution based on the evidence available to us. As Gould has said, Homo sapiens is an entity, not a tendency.

Contrast that, though, with the popular image of e
volution, which amounts to a paradigm of progress: 'lower' life forms rising through time to become 'higher' forms of life, culminating with (who else) 'the glory, jest and riddle of the world', ourselves. So ingrained is this image that endless variants are a regular feature of editorial cartoons:

This is just one of many examples. Why do people keep reading evolution as a principle of progress, when it manifestly isn't? Probably because they want to regard evolution favorably, and because treating evolution as 'progressive' essentially recasts it as an appealing (albeit long-discredited) way of looking at nature, Aristole's scala naturae:

So, the 'missing link' is really like a rung in the ladder shown abpve, a previously-unfilled-in piece of the puzzle, which is imagined (incorrectly) to be linear and progressive. Wonderful, except it is entirely misleading. Properly speaking, 'missing links' is a gloss for a term which is actually useful and not all that controversial within science---transitional forms. And even here the term is widely misunderstood. Alcomber and his colleagues have doubtless found an example of a fossil which has transitional features, but no scientist is saying that this particular creature, or even the population from which this fossil is found, is actually ancestral to present-day populations, or that any living organism is its lineal descendant. And yet that is almost certainly the mental image many people supply when this term ('missing link') is invoked!

1 comment:

Eamon Knight said...

To repeat something I posted over at Sandwalk a little while ago: every science journalist should be force-fed Lovejoy's Great Chain of Being and Gould's Full House (or an equivalent selection of his essays). Then maybe we'd be spared these endless misconceptions about evolution.