There are two ways to interpret this question. The first is whether humans have eaten foods produced by GMO technology, or as scientists call it, genetic engineering. The answer to that is straightforward. We’ve been eating GM crops (GM = genetically modified) and food ingredients produced from them for over 20 years—literally trillions of human meals contain GM ingredients. In spite of a barrage of scary claims about the risks of GMOs made by anti-science advocates, not a single case of harm to humans from eating GMOs has been documented. As environmental activist and writer Mark Lynas noted, “you have a better chance of being hit by a meteor [than being hurt by GM food].”
If the questioner is asking whether GMO technology or genetic engineering has been used on humans, the answer is a little more complicated. If we define GE as using the tools of modern genetics to make permanent changes to an organisms chromosomes then there are two possible classes of changes. Living organisms that depend on sexual reproduction, like humans, are comprised of what biologists call somatic cells which are simply the cells that make up our bodies. These are sometimes called vegetative cells. The other kind of cells are involved in reproduction and are called germ cells. Germ cells give rise to gametes; in mammals the gametes are ova and spermatozoa which combine after mating to make a new individual. The reason this fundamental difference in body versus reproductive cells is important to this discussion is that if the somatic cells are genetically engineered the changes stay with that individual and are not passed on to the progeny and will not be present in future generations. On the other hand, if the germ cells of an individual are genetically altered, those changes can be passed on to progeny.
Genetic changes in germ cells could be used in many useful ways. Many diseases have a genetic basis. Perhaps someday in the future the genes which cause diseases will be knocked out, or genes that are missing or defective will be replaced. If these kinds of changes are made to a prospective parent’s germ cells then their children will not carry the defective or missing genes associated with that genetic disease. Using these technologies it might even be possible someday to allow parents to pick the color of their children’s hair, improve their odds of be tall, or of having a certain eye color. The question immediately arises if we really want to do this? Some have asked is it right (ethical) to make changes that might permanently impact future generations. Where should we draw the line between making health beneficial genetic changes that prevent diseases from changes that cause some to worry that we are playing God? Society needs to answer the ethical and moral questions posed by germ line engineering. Currently, germ cell modification is a subject for research but has not been applied to human subjects. Proposals to engineer humans in this way would not be approved by review boards or regulators. Scientific societies and almost all scientists agree that society is not ready to accept engineered humans at this time.
Somatic cell engineering has, on the other hand, been the subject of a great deal of research. Engineering genetic changes in an individual’s somatic cells could eliminate genetic defects for that single individual. Most of us would accept that eliminating genes that cause sickle cell anemia or other inborn genetic errors from someone who suffers from that disease is ethically equivalent to administering a pharmaceutical; it is curing or preventing a disease in that one person. There are several systems for genetically engineering changes in somatic cells that have been used to advance a handful of products through clinical trials to the market place. There are also billions of dollars being spent in research in this area. A quick Google search or visit to Wikipedia using search term gene therapy will provide those interested in learning more about this exciting new branch of medicine a portal to a wealth of information regarding the many diseases for which researchers are trying to develop solutions.
Germ line engineering has been used to produce improved seeds and animals. GMO or GM crops are examples of successful germ line modification.