Tuesday, November 28, 2006

Review: Genes in Conflict

I've got a piece (registration required) in the current London Review of Books on Genes in Conflict by Austin Burt and Robert Trivers.

The book's a brilliant resource, bringing together what must be pretty much every piece of information on selfish genetic elements, such as transposable elements, selfish sex chromosomes and imprinted genes. These genes can thrive at the expense of the organisms that carry them, causing conflict and selection to operate within genomes and organisms, as well as between them.

Such conflict has led to some extremely odd biology (such as the sperm that can eject the maternal chromosomes from the eggs they 'fertilize'), some extremely fundamental aspects of our biology (such as the uniparental inheritance of mitochondria, and probably some details of mitosis and sex itself), and some extremely interesting potential effects on our behaviour and psychology, caused by different bits of the genome pulling in different directions. I imagine this will be explored further in Trivers' next book, which is apparently going to be about the evolution and uses of self-deception.

This is the sort of book that would work splendidly as an online resource — it doesn't take a linear approach (early on the authors say it can be read in any order, which is a bit dispiriting for a reviewer settling down to read the whole thing), so hyperlinking would be valuable. And this is such a fast-moving field that regular updates would be welcome (such as, say, the power of transposable elements as a creative force in evolution, which is a bit off-message from the book's main thrust, but an exciting area, as a recent N&V feature (registration required) in Nature shows). Magisterial overviews such as this still clearly have a place on academic bookshelves, but they need to cope with the way that the internet has made the information they collate easier to find and access.

Wednesday, November 15, 2006

Leonardo's notebooks

Anyone interested in science would do worse than go to the Leonardo da Vinci exhibtion at London's V&A museum, running until 7 January. I went last week.

The exhibtion, of material from the man's notebooks isn't primarily an aesthetic experience (although there are some beautiful things there). What it's about is giving you an insight into Leonardo's thinking, and the full range of his preoccupations.

Nowadays, the term 'Renaissance man' is applied to any science PhD who's read a novel and got grade 3 clarinet (women tend to do lots of different things without running around giving themselves grand names). This exhibition shows you better than anything I've ever seen what being a Renaissance man really meant. Leonardo treated the artistic, scientific, mathematical, biological, architectural, mechanical, you name it, as all one and the same - often on the same sheet of paper. Designs for musical instruments are alongside those for palaces, and stage sets, which are alongside plans for epic murals, or engines of war, or anatomical drawings, or clouds. Astonishing.

On the science side, it looks very much as if he was thinking about problems, such as finding a shape's centre of gravity, or a volume's solid, that were solved by Newton/Leibniz's invention of calculus. He also seems to have pondered other Newtonian stuff, such as gravity and mechanics. (And he tried to square the circle, and build a perpetual motion machine. Nothing I could see on thurning base metals into gold, though.)

He also did some drawings on the form of trees, river networks, and blood vessels that (looking at things with a biased eye, I admit) intriguingly prefigures the network models of metabolic rate, river networks, and other stuff by West et al. and Banavar et al.

And here's a quote, presented in the exhibition, which could have come straight out of D'Arcy Wentworth Thompson's mouth, and which sums up world view (one of them, anyway) I write about in ITBOAH:

"A bird is an instrument working according to mathematical law."

Pegged to this exhibtion, there's an interesting piece by Guardian art critic Jonathan Jones on how the notebooks ended up in the hands of the British royal family.

Monday, November 06, 2006

Is natural selection a law of physics?

More on applying the physics of statistical mechanics and thermodynamics to ecology and evolution. This paper by Guy Hoelzer and colleagues appeared recently in the Journal of Evolutionary Biology:

On the logical relationship between natural selection and self-organization

…In this study, we attempt to describe the logical framework that relates the general process of self-organization to the specific process of natural selection. We describe natural selection as a mechanism that coordinates the coevolution of species in an ecosystem to effectively capture, process and dissipate solar energy into the earth’s shadow. Finally, we conclude that natural selection is an emergent process founded on the same thermodynamic imperatives that are thought to underlie all self-organization. This perspective suggests … the possibility that there may be a physical basis for understanding the origin of the process of natural selection. Rather than being merely a fluke of nature, the origin of natural selection that may be driven by energy flows across gradients.

As an example of the kind of links between biology, thermodynamics, and self-organization that they are pursuing, Hoelzer et al. give photosynthesis. They point out how good it is at levelling out the gradient of solar energy, and suggesting either that "photosynthesizing life is a statistically favoured component of the biosphere, or that a high-flux channel for light transduction is a favoured endpoint, towards which perturbed ecosystems recover. Physical principles expressed in terms of stable end states imply a natural teleology, which we have suggested (somewhat imprecisely) is the reduction of the spectral and spatial energy gradient imposed by the situation of earth in a solar radiation bath."

They also invoke metabolic scaling theory, which explains living things' energy use in terms of the geometry of transport networks (something similar seems to apply to the geometry of lightning strikes and river basins), and suggest that a taking a self-organizational view is a good way to try and understand why, the more energy an organism uses (whether metabolically, or, for humans, in society), the fewer offspring it has. (More about all this here and in ITBOAH

Other striking quotes:

We offer the conjecture that the truly ultimate explanation for any dynamical event, and the qualities of any emergent dissipative structure, including organisms and ecosystems, is thermodynamic.

Natural selection is to self-organization as language is to communication. Language is not synonymous with communication, yet it is a quantum leap forward in communicative effectiveness. It is also not merely a more complicated for of simpler modes of communication. … Language has emerged from the drive to communicate just as natural selection has emerged from the drive to break down gradients.

Much of this is not particularly new. Dynamic, complex physical systems can take on orderly, structured states, and physicists such as Stuart Kaufmann have long suggested that the same principle applies to living things — that self-organization, as well as, or instead of, natural selection, can explain the complexity and structure of life.

Likewise, it's not a new idea that thermodynamics can explain the structure of life, and that this structure evolves to flatten out energy gradients as much as possible, and degrade energy/produce entropy as quickly as possible.

And biologists have usually resisted these concepts. Natural selection is so successful that bolt-ons from physics seem superfluous. There's no reason to believe that natural selection should maximize anything thermodynamic, and many biologists take issue with the assumptions and predictions of this approach. Someone once pointed out that the reason horses had evolved was to make more horses, not to make horse manure. John Maynard Smith thought harder about these things than most biologists, and (I think) remained sceptical. (Try here or here.)

So either all the current upsurge of this stuff is just a cyclic blip, or we're really inching towards some kind of new insight. I'm not sure which.