How Big Bird Evolved into Little Kiwi
The latest story about flightless birds is so counter-intuitive, maybe it belongs on Sesame Street instead of textbooks.
Staunch Darwin disciple Charles Q. Choi has done it again: written a pro-evolution article for Live Science with a provocative title that borders on silliness: “Closest Living Relative of Ancient Elephant Bird Is Tiny.” He can hardly be blamed, though; he’s just echoing what Aussie biologists said in Science this week, “Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution.” Michael Slezak at New Scientist is playing right along: “Emu-style birds have abandoned flight six times,” his headline reads.
The old story was that flightless birds “evolved” (actually, devolved, since they lost a complex function–flight) on Gondwana, then ran to different areas that later split up. The new story is that the ancestors flew to different continents after the breakup. Choi summarizes,
Ostriches and their flightless relatives are found across the globe not because continental drift forced them apart, but rather because the ancestors of these birds spread across the world through flight, and only later became flightless, researchers say.
Where do “elephant birds” come in? These large flightless birds from Madagascar, known only from fossils, grew up to 10 feet tall. You’d never guess who their cousins are:
After sequencing and analyzing genetic data from two species of elephant bird, scientists unexpectedly discovered the closest living relative of these birds is actually the small kiwi, and not the large ostrich, to which the elephant birds bear a closer physical resemblance.
That’s not the only conundrum. Slezak quotes one of the paleontologists saying, “In both cases, the moa and the elephant bird, the nearest relative is on the other side of the world.” David Penny quips, “It shouldn’t be surprising but it is.”
Nothing is surprising if you have a powerful enough god. From Live Science:
The unexpected relationship between the elephant bird and the kiwi “highlights the power of evolution to produce radically different forms over a relatively short period of time,” Mitchell said. The scientists detailed their findings in the May 23 issue of the journal Science.
The new study suggests that ratites did not evolve from populations of a common flightless ancestor that were separated by continental drift. Rather, it appears these flightless birds surprisingly evolved from ancestors that flew long distances to new corners of the world and then evolved independently to be flightless.
“We have to completely reconsider the origin of ratites as a whole,” Mitchell said. “It totally changes our understanding of how these lineages moved around and arrived at their current homes. They can’t have rafted on continental fragments — they must have flown.”
Totally changing one’s understanding is permissible, as long as the total stays inside evolutionary theory.
“The power of evolution” sends birds around the world, except when they stay put. It evolves flight, except when it evolves flightlessness. It produces radically different forms over a short period of time, except when it keeps animals unchanged for hundreds of millions of years. It produces big cousins, except when it makes them tiny. Its relatives live near one another, except when they live on opposite sides of the world. It totally changes understanding, except when it maintains dogma. Evolution is all-powerful. Evolution works in mysterious ways. Evolution is like a god, but without the purpose.