Genetically engineered organisms

Why I’m not particularly worried about genetically engineered organisms harming people or their ecosystem.

People who do not have a good background in biology often do not understand that living organisms are constantly experiencing random genetic mutations of the same kind that scientists create when they attempt to do genetic engineering. For thousands of years humans have noticed these mutations in their crops, animals and in each other. Further, for thousands of years we have acted to select for desirable genetic mutations and their physical expression (phenotypes) in the offspring of plants, animals and even ourselves by selective breeding. Now, rather than waiting for chance alone to produce useful genetic mutations, we can make them ourselves and use them to improve our crops, our livestock and, perhaps, even cure genetic diseases and cancer.

The following quotation is from The Outer Reaches of Life, by John Postgate (Cambridge University Press, 1994). It does an excellent job of putting into a “real world” perspective the relative importance of the mutant organisms produced by our recent efforts to use the techniques of molecular biology in genetic engineering.

“Gene-transfer processes and their capacity for gene rearrangement provide bacteria with the potential for substantial and rapid genetic change. But there is yet another consideration. Mutation is a very rare event as far as higher organisms are concerned, but is an important part of the everyday biology of bacteria such as Escherichia coli. The reason stems from the fact that the bacteria are extremely numerous and have rather a small complement of genes. Let me illustrate this point with a simple calculation concerning the global population of E. coli living in the human gut.

Humans on an average discharge about 200 grammes of faeces a day. Human faeces contain a surprisingly constant figure of about 100 million E. coli per gramme. Thus a single person produces about 20 billion E. coli per day, almost all freshly grown since the last defecation.

In 1990 there were about 5 billion humans in the world (there are lots more now). The global growth rate of our intestinal E. coli was thus about 100 billion billion (10^20) cells per day.

In the last couple of decades, molecular biologists have established that E. coli possesses enough DNA for about 4000 genes, which seem to be all that it needs to be E. coli.

Mutations which do the organism no serious harm (such as those which lead it to acquire resistance to a drug, or to need some fairly common nutrient) occur spontaneously in multiplying E. coli at frequencies in the range of 1 per 100 thousand to 1 per billion of new progeny. For the sake of argument, say 1 per 10 million.

Obviously, therefore, more than 10 thousand million E. coli genes mutate daily inside humanity. Each mutation signifies an altered gene. Since E. coli contains only 4000 or so genes, it follows that every gene of the gene pool of E. coli traversing the human intestine mutates at least 2.5 billion times daily.

That calculation makes some crude approximations, especially over the spontaneous mutation rate. But it is not more than an order of magnitude wrong: the message is that the daily mutability of E. coli’s collective genetic material is astronomical. Add in the E. coli inhabiting the guts of other mammals, and be informed that stresses experienced when E. coli leaves the gut increase its mutation rate, and the number of mutations gets even larger. The upshot is that among the terrestrial population of E. coli, every possible mutation is occurring an enormous number of times a day.”

Another upshot of Postgate’s calculation is that human activities directed at producing potentially useful mutations in bacteria, plants and animals simply vanish from view when compared with the truly immense numbers of naturally-occurring mutations in the bacteria and viruses living within us and in the wild. Each of these mutations is a natural experiment in genetic engineering. Each of these “experiments” is at least as “dangerous” as the experiments in genetic engineering now taking place in laboratories around the world.

For example, Postgate’s calculation can be used to show that each of us produces 20 x 10^9 (20 billion) E. coli each day and that E. coli mutates at the approximate rate of one mutant gene per 1 x 10^7 (10 million) bacteria. Thus we can calculate that in each of our guts each day there are two thousand mutations in E. coli genes. I wonder if Jeremy Rifkin has ever considered the fact that, each time he travels to give a public lecture on the alleged dangers of genetic engineering, he is releasing two thousand or so mutant strains of E. coli from his own gut into the local public sewer system (I’m assuming here that he spends one day in the city where he speaks and that he is a regular guy). It is very unlikely that the research labs Rifkin is so fond of excoriating release such a number of mutant bacteria into the environment in a year. Should his movements be restricted on the grounds that he is releasing 730,000 mutant bacteria per year into the environment?