Thursday, May 30, 2013

Paleontologists Argue, I Shrug

What, if anything, is a bird? Paleontologists have been arguing this one for a century now, and they are still at it. Ed Yong summarizes:
Consider the origin of birds. There is now overwhelming evidence that birds evolved from small predatory dinosaurs. Hundreds of stunning fossils illustrate the transitions from dino-fuzz to flight feathers and from grasping arms to flapping wings. The avialans (all birds, living and extinct) fit within a group of dinosaurs called the Paraves, which also includes dromaeosaurids (sickle-clawed predators like Velociraptor and Deinonychus) and troodontids (large-brained predators like Troodon). But which of these creatures were the first birds, and which specific group of paravians were their closest relatives? That’s still the subject of heavy debate.
Three groups of paleontologists have recently drawn different family trees for birds and related dinosaurs. The version proposed by Xing Xu, the man behind all those Chinese feathered dinosaur fossils, puts the famous archaeopteryx, long considered the first bird, outside the avialans altogether. This would make this Chinese creature, Aurornis xui, the earliest known bird.

To which the only rational response is to shrug and say "maybe." Our knowledge of these evolutionary connections has exploded in recent decades, and who knows how things will change when the next spectacular fossil turns up? The history of science is full of debates that were waged with great intensity but then quickly forgotten when some good evidence was finally found. Right up until Apollo 11 landed, people were publishing papers staking out positions on what the lunar surface was made of, which is why Armstrong's first words as he went down the ladder were about the quality of the dust.

I have the same position about human evolution, which is that it is just crazy to get invested in which very partial 2-million-year-old skeleton is a human ancestor and which a forgotten side branch. How could we possibly know?

Many people really enjoy having firm opinions, and this is one vice that scientists seem to have in excess. A little humility would serve better than all this wrangling.

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