So, the british Medical Association, and virtually everyone else, has joined the lobby against genetically modified (GM) food. GM maize harms monarch butterflies in the American cornbelt. Our sexuality is under threat from oestrogen-mimics produced in GM soya beans sprayed with herbicide. We feel bullied by big business and suspect government collusion in GM food release without proper safety trials. We fear threats to the ecosystem, the food chain and human health. We fear the escape of foreign genes into the wild. We fear an alien and unnatural technology.
Yet genetic modification is not unnatural: indeed, for those of us still old-fashioned enough to smoke, every time we puff on a ciggie, we inhale the combustion products of a natural GM event which took place millions of years ago somewhere in the Andes. At Queen Mary and Westfield College, University of London, Andrew Leitch and I are studying the evolutionary origin of viral gene fragments we discovered in tobacco and four of its relatives. How did this ancient genetic "accident" happen? Why has it perpetuated during evolution? Answers to these questions may also help to assess artificial GM escapes into the wild.
Genes are handed on from parents to offspring and during this "vertical transmission," natural genetic changes (mutations) result in variation in the offspring. Natural selection for the more successful variants results in the formation of new species. This is evolution as Charles Darwin presented it, with the added spice of genes from Gregor Mendel plus our modern understanding of both DNA, as the physical embodiment of genetic information, and of how mutations occur.
Language also changes during "vertical transmission," for example, from Chaucer's to Shakespeare's to our modern English. But just as English has acquired and assimilated foreign words -"robot" from Czech, "pundit" from Hindi, "guerrilla" from Spanish-so organisms can acquire foreign genes from other species, a process known as "horizontal transmission."
Horizontal gene transfer happens frequently in nature. For example, soil bacteria produce antibiotics for waging chemical warfare upon their competitors. Antibiotic-resistance genes, which equip these bacteria with antidotes against their own toxins, are transferred naturally from these warmongers to other bacteria, including human and animal bacterial pathogens. So, when antibiotics are used by doctors to treat bacterial infection those pathogens which have naturally acquired these resistance genes can, alas, survive.
Horizontal transmission can also be exploited artificially for our benefit. For example, it can equip GM crops with resistance to insect pests, herbicides and viruses. In a model study we made virus-resistant GM tobacco plants. We inserted a viral replication gene into the plant's DNA, and designed it to prevent invading viruses from producing the replication protein. The experiment worked: the GM plants prevented the invaders from producing more copies.
But then, ironically, we found that DNA sequences very similar to the ones we were putting in artificially were already present in hundreds of apparently inert copies in non-engineered tobacco plants. We also found these sequences in other plants, but only ones that were very close relatives of tobacco. In tobacco and its four close relatives they are found in the same place in a particular chromosome and are so similar that they could only have arisen from a single event. Tobacco is a hybrid of two species, rather like the English language which, following the Norman invasion, became a hybrid of two languages. Norman invasions are frequent events among plants: many plant species are natural hybrids.
Our results suggest that one fine morning in May, about 5m years ago, an aphid bit a plant and transmitted the virus. Some infected cells survived but not before a segment of the virus had inserted itself into a single chromosome. This GM plant cell must have given rise to cells that developed into a flower that produced seeds carrying this new DNA. These seeds germinated and new plants arose. Either by chance, or by virtue of a new advantage, plants carrying these genes came to predominate in the population so that eventually all members of this species came to carry them. This plant was the ancient ancestor which then evolved into the five distinct species that carry these sequences today.
So GM is not in itself alien or unnatural, nor is the spread of foreign genes in the wild. Nature has already performed such experiments to generate genetic variation. The issue is whether the particular gene chosen for introduction to a new species gives the new GM plant a competitive advantage which leads to its spread. (Esperanto is an example of an "engineered" language with no selective advantage that foundered, leaving remnants such as a faded shop-front for the Esperanto Society somewhere in Holland Park.)
Of course, GM, like most things, can be dangerous if it is mishandled. Whether or not a GM crop perturbs the ecosystem or poisons our food depends upon the specific foreign gene inserted. But there is nothing inherently sinister about it. And we should see these new risks in the broader context of our current crops, which are awash with agrochemicals, and of the spread of genes from cultivated crops into the wild over the past 12,000 years of human agriculture.
Species change, language changes, yet we are romantics and lament it. Years later, I am still grieving over the plastic replacement of a metal lid on the Marmite jar.
