Saturday, May 10, 2008

Nout as queer as the platypus?

I spotted something in a newspaper today that on the surface seemed positive but scratch below the surface and it just confirms the shallow attitude of the media to serious and important scientific endeavours these days. You can read the article accompanying the paper here.

The article was about the recent decoding of the platypus genome, and a paper that has just been published entitled "Genome analysis of the platypus reveals unique signatures of evolution."; so far so good, at least it's an article in the mainstream media about a serious scientific principal, i.e. evolution, but then I read further, "the egg-laying critter is a genetic pot-pourri — part bird, part reptile and part lactating mammal", wrong, wrong, wrong. Don't these people know anything about evolution, for a start species aren't "mixed up" as this quote implies, like some giant tumble drier or a marvel comic, half man, half spider etc. secondly they simply miss the whole point of the paper which is about lineage and what is "similar" about this creature to other mammals, not just its unique phenotype (physical body).

The platypus is NOT part bird, in fact birds are an independent and unrelated lineage, birds and the platypus certainly had a common ancestor but the evolutionary trajectory split around 315ma (million years) ago when the Synapsids and the Sauropsids went their separate ways. It is true to say it's part reptile since it directly descends from reptiles (reptiles are much older than birds), you can also equally say that we are part reptile also since we share a big chunk of that lineage up to a point around 160ma ago deep in the Mesozoic era. (see diagram below)

The platypus is certainly unique it never lost the egg producing machinery that the rest of the mammalian tree did, it also evolved the ability to produce venom as certain of its reptilian ancestors do, but interestingly all other mammals did not. This paper is a fabulous confirmation of our present understanding of evolution and as more and more genomes are decoded that confirmation gets stronger and stronger, an absolutely fascinating subject.

Some of the hard numbers stick out, for example the platypus has roughly 18,000 genes, slightly less than us (we have around 20,000), approximately 82% of the genome is shared between marsupials, eutherians, reptiles and monotremes etc. and about half the genes are "junk" (which doesn't necessarily mean pointless). All of this adds weight to the current picture of common lineage derived from the molecular biology, which in turn overwhelmingly confirms the same conclusions reached via other paths, i.e. the fossil record, comparative anatomy and animal distribution patterns etc.

I'm sure Charles Darwin would be astounded (and just a little smug) if he were alive today!

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