Phylogeny: Rewriting evolution
Tiny molecules called microRNAs are tearing apart traditional ideas about the animal family tree.
Elie Dolgin
27 June 2012
Kevin Peterson has kicked many mammals, including the Alaskan Brown Bear, off their traditional perch on the evolutionary tree.
DANA SMITH
Kevin Peterson grabs a pen and starts to scribble an evolutionary tree on the paper tablecloth of a bar in Hanover, New Hampshire. Drawing upside down to make it easier for me to see, he maps out the standard phylogenetic tale for placental mammals. First, Peterson scratches a line leading to elephants, which branched away from the rest of the placentals around 90 million years ago. Then came dogs, followed by primates (including humans) and finally rodents — all within a frenetic 20 million years. This family tree is backed up by reams of genomic and morphological data, and is well accepted by the palaeontological community. Yet, says Peterson, the tree is all wrong.
A molecular palaeobiologist at nearby Dartmouth College, Peterson has been reshaping phylogenetic trees for the past few years, ever since he pioneered a technique that uses short molecules called microRNAs to work out evolutionary branchings. He has now sketched out a radically different diagram for mammals: one that aligns humans more closely with elephants than with rodents.
“I've looked at thousands of microRNA genes, and I can't find a single example that would support the traditional tree,” he says. The technique “just changes everything about our understanding of mammal evolution”.
Peterson didn't set out to rewrite textbooks. A mild-mannered but straight-talking Montanan, Peterson had made a quiet career studying how bilateral body plans originated more than 500 million years ago. He has a particular interest in marine invertebrates and had intended to stick with that relatively obscure branch of the animal tree. But a chance investigation of microRNAs in microscopic creatures called rotifers led him to examine these regulatory molecules in everything from insects to sea urchins. And as he continues to look, he keeps uncovering problems, from the base of the animal tree all the way up to its crown.
That has won him many critics, but also some strong supporters. “Peterson and his colleagues have demonstrated that microRNAs are a powerful tool in determining the relationships of major animal groups,” says Derek Briggs, director of the Yale Peabody Museum of Natural History in New Haven, Connecticut.
Now, together with his colleagues around the world, Peterson is putting it all on the line with mammals. “If we get this wrong, all faith that anyone has in microRNAs [for phylogenetics] will be lost,” says Philip Donoghue, a palaeobiologist at the University of Bristol, UK, who has teamed up with Peterson. And there is more at stake than just the technique. “It could well be the end of all our careers,” he says.
Fossil find
If Peterson does end up switching careers, it won't be the first time. In the early 1990s, he was working the night shift unloading trucks at a freight company in his hometown of Helena, Montana, trying to figure out what to do with his life. He had recently graduated with a pre-medical degree from a local liberal arts college, but he knew he didn't want to become a doctor. Then, rummaging in his parents' barn, he happened on the first fossil he had ever collected, as a four-year-old: a crinoid, or sea lily, about the size of a button. “After I found it, I knew right away that this was what I wanted to do,” he says. “I applied to graduate school the next week.”
He soon enrolled in a PhD programme in the Department of Earth and Space Sciences at the University of California, Los Angeles. There, he teamed up with developmental geneticists Eric Davidson and Andrew Cameron at the California Institute of Technology in Pasadena, and over the course of his graduate and postdoctoral work the three men developed a provocative idea, dubbed the set-aside cell hypothesis 1. They posited that the ancestor of modern-day animals was a larva-like creature containing a group of undifferentiated cells that retained the capacity to give rise to the spectrum of adult body types seen during the Cambrian explosion. The idea subsequently came under fire from the evolutionary and developmental-biology communities.
A few years after moving to Dartmouth in 2000 to start his own lab, Peterson was looking for a way to test the hypothesis when he became intrigued with microRNAs. First discovered in 1993 by Victor Ambros, now at the University of Massachusetts Medical School in Worcester, these short, hairpin-shaped molecules bind to messenger RNAs and stop them from making proteins. A team that included Davidson had shown that a microRNA called let-7 was present in animal lineages that had bilateral body plans but not in simpler organisms such as jellyfish and sponges 2, hinting that microRNAs could hold the secret to morphological complexity.
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Read more here/Leia mais aqui: Nature
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NOTA DESTE BLOGGER:
Um pequeno artigo desses contrariando o DOGMA darwinista da Árvore da Vida saindo na renomada publicação científica Nature sinaliza o que? Uma revisão profunda nas especulações transformistas de Darwin de ancestralidade comum (descendência com modificação) que é ferreamente defendido pela Nomenklatura científica?
Fui, nem sei por que, rindo da cara da Galera dos meninos e meninas de Darwin que, quando afirmei ser a Árvore da Vida de Darwin uma miragem ideológica, caíram de pau neste blogger na blogosfera. E fui rachando de rir dos signatários do Manifesto da Sociedade Brasileira de Genética sobre Ciência, Criacionismo e Design Inteligente: foram apanhados epistemologicamente de calças nas mãos!!!
Mais uma vez este blogger é vindicado por um cientista evolucionista honesto!
Um pequeno artigo desses contrariando o DOGMA darwinista da Árvore da Vida saindo na renomada publicação científica Nature sinaliza o que? Uma revisão profunda nas especulações transformistas de Darwin de ancestralidade comum (descendência com modificação) que é ferreamente defendido pela Nomenklatura científica?
Fui, nem sei por que, rindo da cara da Galera dos meninos e meninas de Darwin que, quando afirmei ser a Árvore da Vida de Darwin uma miragem ideológica, caíram de pau neste blogger na blogosfera. E fui rachando de rir dos signatários do Manifesto da Sociedade Brasileira de Genética sobre Ciência, Criacionismo e Design Inteligente: foram apanhados epistemologicamente de calças nas mãos!!!
Mais uma vez este blogger é vindicado por um cientista evolucionista honesto!
