Tuesday, November 21, 2006

 

Bushes in the Tree of Life (Sean B. Carroll and Antonis Rokas)

An open access/free paper published by PLoS Biology:

Bushes in the Tree of Life
by Antonis Rokas, Sean B. Carroll* (bio)

Genome analyses are delivering unprecedented amounts of data from an abundance of organisms, raising expectations that in the near future, resolving the tree of life (TOL) will simply be a matter of data collection. However, recent analyses of some key clades in life's history have produced bushes and not resolved trees. The patterns observed in these clades are both important signals of biological history and symptoms of fundamental challenges that must be confronted. Here we examine how the combination of the spacing of cladogenetic events and the high frequency of independently evolved characters (homoplasy) limit the resolution of ancient divergences. Because some histories may not be resolvable by even vast increases in amounts of conventional data, the identification of new molecular characters will be crucial to future progress.

"... there is, after all, one true tree of life, the unique pattern of evolutionary branchings that actually happened. It exists. It is in principle knowable. We don't know it all yet. By 2050 we should - or if we do not, we shall have been defeated only at the terminal twigs, by the sheer number of species." Richard Dawkins [1] (author of The God Delusion: Amazon Astore UK | US)

Who are tetrapods' closest living relatives? Which is the earliest-branching animal phylum? Answers to such fundamental questions would be easy if the historical connections among all living organisms in the TOL were known. Obtaining an accurate depiction of the evolutionary history of all living organisms has been and remains one of biology's great challenges.

The discipline primarily responsible for assembling the TOL- molecular systematics - has produced many new insights by illuminating episodes in life's history, posing new hypotheses, as well as providing the evolutionary framework within which new discoveries can be interpreted [2]. Molecular systematics has surmounted the confusion stemming from comparisons of morphologically disparate species to reveal unexpected evolutionary relationships such as the Afrotheria, a clade composed of strikingly different mammals including elephants, aardvarks, manatees, and golden moles [3]. It has also aided the placement of the history of life in a temporal framework, shedding light on key evolutionary events independently of - and in many cases well before - the availability of fossil or biogeographic evidence. A notable example is the discovery that the Hawaiian drosophilid lineage predates by many million years the oldest extant Hawaiian island, having originated on islands now submerged [4].

Continued at "Bushes in the Tree of Life"
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*The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution By Sean B. Carroll Amazon UK | US - see "'The Making of the Fittest' (Excerpt, Audio Interview, Review)"

Books on 'Genetics and Evolution' from the Science and Evolution Bookshop: UK | US

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