(cm) The male follows the female, taps gently on her back with his front legs, courts her with gossamer-winged melodies, licks her genitals and, finally, curls her back so that she will let him mate with her. This sophisticated ritual is a description of a male fruit fly's courtship programme. Programme? The metaphor seems justified. An Austrian research group recently showed how a single gene acts as a switch to activate the male Drosophila's reproductive behaviour (1).

This is the result of work carried out by scientists in Austria who investigated the so-called "fruitless" gene. This gene is processed, or spliced, in different ways in the two sexes. If the genes of a female fruit fly are genetically modified in such a way that male genes are produced she acts like a male. Her courtship of other females matches that of the best Drosophila Casanova–apart from the fact that she licks less. On the other hand, interest in females is wiped out in a male fruit fly manipulated to produce the female fruitless gene.

While the underlying research was elegantly done and gripping, he was not overly surprised that complex behaviour can be steered by a single gene, was the comment of the ETH evolutionary biologist Paul Schmid-Hempel (2). It was already known that a single gene could direct a host of behaviour in bees or mice. Unfortunately, this was also true for some human hereditary disorders, such as Huntington's chorea.

It is important to note that there is not necessarily a connection between the levels of "complex" from a human point of view and the genetic mechanism for any given characteristic. A simple, linear arrangement of so-called homeo-boxes in the genome could potentially give rise to a huge variety of blueprints.

According to Schmid-Hempel the new research throws no really new light on the age-old debate of nature versus nurture. Most biologists agree that the phenotype is a product of both environment and genes. In the end, as far as individual characteristics are concerned, it was only a question of determining the degree of influence exercised by these two issues. It was far more interesting, so the ETH scientist, to investigate the frequency of the occurrence in living organisms of genetic switches like that described in the publication, and in their connections. As an evolutionary biologist he also asked himself what advantage such a form of regulation would bring in the struggle for survival. And yet another question followed from this, namely how many characteristics organisms can "afford" to have that are steered by such simple processes. It could be that it is not worthwhile for all species to have such simple reproductive behaviour patterns.

The head of the research team in Vienna, by the by, is none other than Barry Dickson. He concluded his PhD in Zurich under the supervision of the soon-to-be ETH president, Ernst Hafen. Dickson took over a research group at the University of Zurich before moving to Austria.