AVIAN EVOLUTION

20 Dec

Edward Wilson put his and the lives of his companions, ‘Birdie’ Bowes and Apsley Cherry-Garrard, at risk, when they made their scientific expedition to obtain specimens of very early penguin eggs in 1911. The three survived darkness, temperatures down to minus 76° F and a surface snow like sand, that held progress at little more than a mile on some days day. The sortie which lasted 5 weeks, was the subject of Cherry-Garrard’s book ‘The Worst Journey in the World’
Edward Wilson wanted to investigate the evolution of birds. Haekel had postulated that species pass through their early evolution in the embryo form and Wilson thought if he could get very early eggs he might find evidence of teeth or other evidence, that threw light on avian development. Had birds actually descended from dinosaurs? He chose penguins because, as they were flightless, he thought they were amongst the most primitive of birds. In spite of his fantastic efforts he did not find evidence to support the theory.
Now an international investigation The Avian Phylogenomics Consortium has revealed how birds evolved after the mass extinction of dinosaurs. After the asteroid hit some 65 million years ago, larger birds were exterminated but a few feathered species remained. These had an unrivalled opportunity to diversify.
The Consortium undertook the mass genome sequencing that has done much to explain the avian tree. Scientists examined small pieces of flesh from 45 bird species that had come from museums around the world. They were able to extract the birds’ genomes and add these to genomes of three species that had been previously sequenced. The genomes were compared and arranged into a family tree. The results of this groundbreaking work have been published extensively recently. Apparently it took nine computers the equivalent of 400 years of processor time to compare the genomes and arrange them in an avian tree.
As Wilson wished to investigate birds ARE descended from toothed dinosaurs, (as was shown in the fossil bird Archaeopteryx), but this analysis shows that their common ancestor lost their teeth more than 100 million years ago. A number of genes that allow bird song is similar to those that give humans the ability to speak.
This study throws light also on Emperors, Wilson’s particular interest. Emperors possess genes that make proteins for feathers, so that they have a dense coat that allows then to survive sub zero temperatures. The Emperor male, who nurtures his chick for weeks in the caterwauling gloom of the Antarctic winter, has three genes involved in lipid metabolism, which help it survive his ordeal without food.
Penguins evolved about 60 million years ago and have wonderfully survived ever since.

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