Posted by: Dan | February 10, 2009

15 Gems of Evolutionary History

I wanted to link to this for Darwin’s Day, but would have forgotten if I hadn’t browsed through John Logsdon’s Sex, Genes & Evolution. In the first issue of 2009 of Nature, its editors published a 17-page article entitled “15 Evolutionary Gems“.

There’s a whole collection of essays cover a wide variety of ways to look at the theory of evolution and its significance. From the introduction to the Gems article itself:

Given that the concepts and realities of Darwinian evolution are still challenged, albeit rarely by biologists, a succinct briefing on why evolution by natural selection is an empirically validated principle is useful for people to have to hand. We offer here 15 examples published by Nature over the past decade or so to illustrate the breadth, depth and power of evolutionary thinking. We are happy to offer this resource freely and encourage its free dissemination.

I particularly liked gem #3: The Origin of Feathers:

One of the objections to Charles Darwin’s theory of evolution was the lack of ‘transitional forms’ in the fossil record — forms that illustrated evolution in action, from one major group of animals to another. However, hardly a year after the publication of On the Origin of Species, an isolated feather was discovered in Late Jurassic (about 150 million years old) lithographic limestones of Solnhofen in Bavaria, followed in 1861 by the first fossil of Archaeopteryx, a creature with many primitive, reptilian features such as teeth and a long, bony tail — but with wings and flight feathers, just like a bird.

Although Archaeopteryx is commonly seen as the earliest known bird, many suspected that it was better seen as a dinosaur, albeit one with feathers. Thomas Henry Huxley, Darwin’s colleague and friend, discussed the possible evolutionary link between dinosaurs and birds, and palaeontologists speculated, if wildly, that dinosaurs with feathers might one day be found.

In the 1980s, deposits from the early Cretaceous period (about 125 million years ago) in the Liaoning Province in northern China vindicated these speculations in the most dramatic fashion, with discoveries of primitive birds in abundance — alongside dinosaurs with feathers, and feather-like plumage. Starting with the discovery of the small theropod Sinosauropteryx by Pei-ji Chen from China’s Nanjing Institute of Geology and Palaeontology and his colleagues, a variety of feather-clad forms have been found. Many of these feathered dinosaurs could not possibly have flown, showing that feathers first evolved for reasons other than flight, possibly for sexual display or thermal insulation, for instance. In 2008, Fucheng Zhang and his colleagues from the Chinese Academy of Sciences in Beijing announced the bizarre creature Epidexipteryx, a small dinosaur clad in downy plumage, and sporting four long plumes from its tail. Palaeontologists are now beginning to think that their speculations weren’t nearly wild enough, and that feathers were indeed quite common in dinosaurs.

The discovery of feathered dinosaurs not only vindicated the idea of transitional forms, but also showed that evolution has a way of coming up with a dazzling variety of solutions when we had no idea that there were even problems. Flight could have been no more than an additional opportunity that presented itself to creatures already clothed in feathers.

Gems 9 (Differential dispersal in wild birds), and 12 (Darwin’s Galapagos finches) are excellent as well, providing examples of sympatric and allopatric speciation in birds, respectively.


Responses

  1. Since a flight feather is a highly specialized variation of the basic feather plan it must have happened that feathers evolved ‘for’ some other purpose. Sexual display is possible but that can more easily be accomplished with skin colour, it doesn’t need a new physiological structure.
    Since scales on a reptile keep parasites at bay, it may be that feathers are an improvement on that plan.
    The likeliest thing? A thing with feathers is warmer in the cold so it needs less food. Most animals die of starvation, feathers would be a really big deal.


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