from the mother or the father – implying a sex-specific ‘imprint’ on the gene. And one study seemed to find a sex-specific effect on the mortality of Swedes according to how hungry their grandparents were when young. From a small number of such cases, none with very powerful results, some modern Lamarckians began to make extravagant claims for the vindication of the eighteenth-century French aristocrat. ‘Darwinian evolution can include Lamarckian processes,’ wrote Eva Jablonka and Marion Lamb in 2005, ‘because the heritable variation on which selection acts is not entirely blind to function; some of it is induced or “acquired” in response to the conditions of life.’
But the evidence for these claims remains weak. All the data suggest that the epigenetic state of DNA is reset in each generation, and that even if this fails to happen, the amount of information imparted by epigenetic modifications is a minuscule fraction of the information imparted by genetic information. Besides, ingenious experiments with mice show that all the information required to reset the epigenetic modifications themselves actually lies in the genetic sequence. So the epigenetic mechanisms must themselves have evolved by good old Darwinian random mutation and selection. In effect, there is no escape to intentionality to be found here. Yet the motive behind the longing to believe in epigenetic Lamarckism is clear. As David Haig of Harvard puts it, ‘Jablonka and Lamb’s frustration with neo-Darwinism is with the pre-eminence that is ascribed to undirected, random sources of heritable variation.’ He says he is ‘yet to hear a coherent explanation of how the inheritance of acquired characters can, by itself, be a source of intentionality’. In other words, even if you could prove some Lamarckism in epigenetics, it would not remove the randomness.
Culture-driven genetic evolution
In fact, there is a way for acquired characteristics to come to be incorporated into genetic inheritance, but it takes many generations and it is blindly Darwinian. It goes by the name of the Baldwin effect. A species that over many generations repeatedly exposes itself to some experience will eventually find its offspring selected for a genetic predisposition to cope with that experience. Why? Because the offspring that by chance happen to start with a predisposition to cope with that circumstance will survive better than others. The genes can thereby come to embody the experience of the past. Something that was once learned can become an instinct.
A similar though not identical phenomenon is illustrated by the ability to digest lactose sugar in milk, which many people with ancestors from western Europe and eastern Africa possess. Few adult mammals can digest lactose, since milk is not generally drunk after infancy. In two parts of the world, however, human beings evolved the capacity to retain lactose digestion into adulthood by not switching off genes for lactase enzymes. These happened to be the two regions where the domestication of cattle for milk production was first invented. What a happy coincidence! Because people could digest lactose, they were able to invent dairy farming? Well no, the genetic switch plainly happened as a consequence, not a cause, of the invention of dairy farming. But it still had to happen through random mutation followed by non-random survival. Those born by chance with the mutation that caused persistence of lactose digestion tended to be stronger and healthier than their siblings and rivals who could digest less of the goodness in milk. So they thrived, and the gene for lactose digestion spread rapidly. On closer inspection, this incorporation of ancestral experience into the genes is all crane and no skyhook.
So incredible is the complexity of the living world, so counterintuitive is the idea of boot-strapped, spontaneous intricacy, that even the most convinced Darwinian must, in the lonely hours of the night, have moments of doubt. Like Screwtape the devil whispering in the ear of a believer, the ‘argument from personal incredulity’ (as Richard Dawkins calls it) can be very tempting, even if you remind yourself that it’s a massive non sequitur to find divinity in ignorance.
For certainly the elements of things do not collect
And order their formations by their cunning intellect,
Nor are their motions something they agree upon or propose;
But being myriad and many-mingled, plagued by blows
And buffeted through the universe for all time past,
By trying every motion and combination, they at last,
Fell into the present form in which the universe appears.
Lucretius, De Rerum Natura, Book 1, lines 1021–7
An especially seductive chunk of current ignorance is that concerning the origin of life. For all the confidence with which biologists trace the emergence of complex organs and organisms from simple proto-cells, the first emergence of those proto-cells is still shrouded in darkness. And where people are baffled, they are often tempted to resort to mystical explanations. When the molecular biologist Francis Crick, that most materialist of scientists, started speculating about ‘panspermia’ in the 1970s – the idea that life perhaps originated elsewhere in the universe and got here by microbial seeding – many feared that he was turning a little mystical. In fact he was just making an argument about probability: that it was highly likely, given the youth of the earth relative to the age of the universe, that some other planet got life before us and infected other solar systems. Still, he was emphasising the impenetrability of the problem.
Life consists of the capacity to reverse the drift towards entropy and disorder, at least locally – to use information to make local order from chaos while expending energy. Essential to these three skills are three kinds of molecule in particular – DNA for storing information, protein for making order, and ATP as the medium of energy exchange. How these came together is a chicken-and-egg problem. DNA cannot be made without proteins, nor proteins without DNA. As for energy, a bacterium uses up fifty times its own body weight in ATP molecules in each generation. Early life must have been even more profligate, yet would have had none of the modern molecular machinery for harnessing and storing energy. Wherever did it find enough ATP?
The crane that seems to have put these three in place was probably RNA, a molecule that still plays many key roles in the cell, and that can both store information like DNA, and catalyse reactions like proteins do. Moreover, RNA is made of units of base, phosphate and ribose sugar, just as ATP is. So the prevailing theory holds that there was once an ‘RNA World’, in which living things had RNA bodies with RNA genes, using RNA ingredients as an energy currency. The problem is that even this system is so fiendishly complex and interdependent that it’s hard to imagine it coming into being from scratch. How, for example, would it have avoided dissipation: kept together its ingredients and concentrated its energy without the boundaries provided by a cell membrane? In the ‘warm little pond’ that Charles Darwin envisaged for the beginning of life, life would have dissolved away all too easily.
Don’t give up. Until recently the origin of the RNA World seemed so difficult a problem that it gave hope to mystics; John Horgan wrote an article in Scientific American in 2011 entitled ‘Psst! Don’t Tell the Creationists, But Scientists Don’t Have a Clue How Life Began’.
Yet today, just a few years later, there’s the glimmer of a solution. DNA sequences show that at the very root of life’s family tree are simple cells that do not burn carbohydrates like the rest of us, but effectively charge their electrochemical batteries by converting carbon dioxide into methane or the organic compound acetate. If you want to find a chemical environment that echoes the one these chemi-osmotic microbes have within their cells, look no further than the bottom of
