Philip Kitcher

In February 1943, Erwin Schrödinger delivered a series of three lectures in Dublin. A year later, they were published as a book, under the title What Is Life?, so ensuring that Schrödinger’s ideas reached an audience far larger than the four hundred – a number, he wryly notes, which ‘did not substantially dwindle’ over the three lectures – who...

‘Each week I plot your equations dot for dot, xs against ys in all manner of algebraical relation, and every week they draw themselves as commonplace geometry, as if the world of forms were nothing but arcs and angles. God’s truth, Septimus, if there is an equation for a curve like a bell, there must be an equation for one like a bluebell, and if a bluebell, why not a rose?’ So says Lady Thomasina Coverly, the heroine of Tom Stoppard’s Arcadia, to her tutor Septimus Hodge. Her question was echoed a century after her (fictitious) life by the unorthodox biologist D’Arcy Wentworth Thompson, whose mathematical investigations of the living world were collected in On Growth and Form, published in 1917. Although they have excited the admiration of some important thinkers, including Alan Turing and the biologists John Tyler Bonner and Stephen Jay Gould, Thompson’s ideas do not figure prominently in the biological curriculum or the mainstream of research.‘

Organisms that contribute to the reproductive success of their species by doing things that decrease the size of their own brood appear to be inevitable losers in the Darwinian struggle. Since the 19th century, biologists have regarded the evolutionary possibility of altruism as an important theoretical puzzle, and in past decades, it has become clear that it can’t be solved by vague appeals to the idea that co-operative behaviour is good for the flock, the herd or the species. There are alternatives, however. If altruists direct their helpful behaviour towards relatives, then the genes associated with altruism may spread, because they are present in the beneficiaries and transmitted to their offspring; or if today’s altruist is tomorrow’s recipient, the present loss may be made up with interest. Models of kin selection and reciprocal altruism are widely regarded as solving the puzzle.

From the late seventies to the mid-Nineties, biological orthodoxy insisted that the artificial production of animals with an identical complement of nuclear genes – clones, in the vernacular – could only be achieved by means of the transfer of nuclei from embryonic cells, and then only in non-mammalian species. There were excellent grounds for insisting on the impossibility of cloning from adult cells. For, although virtually all the cells in a mature animal contain the same complement of genes, cellular differentiation, the process by which the cells of different systems and tissues take on their distinctive properties, modifies the nuclear DNA in such a way that some regions are effectively silenced. In consequence, nuclei from adult cells were not supposed to be able to direct normal embryonic growth – which accounted for the disappointing results of transplantation experiments using adult nuclei, i.e. the deaths of embryos at early stages.