The other day one of my friends sent me a link to this discussion of a recently published paper. (‘Published’ in the sense that it’s available through archiv, which I gather means it hasn’t been through peer review.) The actual paper is available here. Basically, the authors claim that life has increased in complexity – they’ve used genome size as their measure – as it’s evolved, and that extrapolating that trend backwards suggests that life evolved prior to the formation of the solar system.
But is genome size a particularly good proxy for complexity? Here’s the graph that underpins the conclusions reached by Sharov & Gordon:
Do you see what they’ve done there? ‘Worms’ – which worms? For after all, there are a lot of them: at least 10,000 species of flatworms, more than 80,000 species of roundworms (aka nematodes), and another 10,000 or so annelids (including the familiar earthworm), not to mention the less familiar taxa such as velvet worms & the priapulids. As for the arthropods – well, good old Daphnia has more functional genes than we do. (The poetical Cuttlefish has a nice take on this story here.)
And I see that plants & protists have been left out altogether – unless they’ve been lumped in under the general heading ‘eukaryotes’. Which is strange, because the overall genome size varies by 5 orders of magnitude** across the eukaryotes so far studied, so using a whole bunch of data points instead of the collective average, would make more sense. Unless that would spoil the nice straight line? (**Having said that, much of that variation is due to the number of introns & the quantity of non-coding DNA; however, the various regulatory sequence regions must surely come under the authors’ heading of ‘functional non-redundant genome’?)
I had also thought, on reading the review, that we were probably looking at an argument for panspermia. And I was right. This and other conclusions are presented in the abstract, & I note a certain amount of hubris in the assumption that humanity represents the only possibility of intelligent life in our universe (my emphasis).
(1) life took a long time (ca. 5 billion years) to reach the complexity of bacteria; (2) the environments in which life originated and evolved to the prokaryote stage may have been quite different from those envisaged on Earth; (3) there was no intelligent life in our universe prior to the origin of Earth, thus Earth could not have been deliberately seeded with life by intelligent aliens; (4) Earth was seeded by panspermia; (5) experimental replication of the origin of life from scratch may have to emulate many cumulative rare events; and (6) the Drake equation for guesstimating the number of civilizations in the universe is likely wrong, as intelligent life has just begun appearing in our universe.
A.A.Sharov & R.Gordon (2013) Life Before Earth arXiv:1304.3381v1
PS Strangely, in a paper supposedly about biological evolution, the latter part of the article goes on to discuss technological (ie cultural) evolutionary change – I’m not convinced that it’s appropriate to segue between a claimed link for genetic complexity & time, into the undoubted complexity and rapid ‘evolution’ of technology; apples & oranges, guys.