Oct 13 2016

GMOs and Horizontal Gene Transfer

horizontal-gene-transferPeople reject genetically modified organisms as food (GMOs) for a variety of reasons, but the single most cited reason is the false belief that they are unhealthy. That specific belief also represents the single greatest disconnect between the opinion of scientists and of the general public in a 2015 Pew poll, greater than evolution, climate change, or vaccine safety.

The reason for this disconnect is that the public is relying upon their intuition, rather than scientific knowledge, to arrive at their conclusion. Further, that intuition has been hijacked by a deliberate anti-GMO campaign orchestrated by misguided environmentalists and by the organic food lobby to help promote their brand.

As Stefaan Blancke and his coauthors argue in the above article:

This intuitive reasoning includes folk biology, teleological and intentional intuitions and disgust.

One of the primary “folk biology” talking points of the anti-GMO crowd is that it is “unnatural” to place genes from one species into a distant species. No further reasoning is offered to defend this position – just the invocation of what is “natural” seems to be enough. Those who defend the scientific position often point out that this irrelevant, just a manifestation of the appeal to nature fallacy. Whether or not something occurs in nature does not determine if it is good or bad for human health.

In fact, most plants evolved toxins and poisons specifically to be harmful to animals and things that would eat them. Humans greatly expanded the number of plants they can eat by artificially and dramatically changing those plants, reducing natural toxins and improving flavor and nutritive value.

The anti-GMO crowd rejects that argument, however, saying that there is a difference between changing a plant slowly over time through breeding and cultivation vs changing a plant quickly through direct genetic manipulation. But again, they are just invoking their intuition, and not any specific scientific reality.

Horizontal Gene Transfer

There is another, equally fatal, flaw to the argument that GMOs are “unnatural” because distant species do not exchange genes in nature – it’s wrong.  Biologists refer to the transmission of genes from parent to child as vertical gene transmission. Likewise, transfer of genes from one organism to another not through parentage is referred to as horizontal gene transfer.

Genetic modification is simply a technique for accomplishing directed horizontal gene transfer, but such exchange of genetic material happens all the time in nature, without any human intervention, and even across kingdoms.

This can happen partly because another bit of anti-GMO folk biology is also completely wrong. The infamous “fishmato” invokes disgust in some because of their false intuition that fish genes do not belong in tomatoes. In fact, 40% of Americans surveyed believed that a tomato modified with a fish gene would taste fishy. (Meanwhile, 22% of Canadians in another survey thought they would taste fishy, but 30% in that same survey did not think that regular tomatoes have genes.)

The scientific reality is very different. There is, in fact, no such thing as a “fish gene.” Sure, fish have genes, but their genes are the same as any other gene. Every living organism on earth shares the same genetic structure, machinery, and genetic code. We also share an evolutionary history. Fish and tomatoes already share about 60% of their genes (depending on how you count it, but that is a reasonable estimate). You and tomatoes share about 60% of your genes.

There is nothing inherently “fishy” about the genes in fish, and transferring a “fish gene” into a plant will not transfer some fishy essence with it. It will simply transfer whatever protein that gene codes for.

As a clear demonstration that genes can comfortably be swapped between different species (species that cannot breed) and even between kingdoms, there are many examples from nature. In fact, every species has genetic material that it acquired in their evolutionary history from horizontal gene transfer. But here are some examples of functional genes acquired this way.

Viruses that infect bacteria often “steal” genes from those bacteria, but a recent study shows that one such virus, that infects bacteria that live in insects and spiders, acquired genes from a black widow spider for a poison that enables it to punch through cell walls.

Another recent study demonstrates that an amoeba, Paulinella, which is photosynthetic, took genes from engulfed bacteria to replace broken genes that it needed. Specifically, Paulinella has an endosymbiotic organelle that does the photosynthesis (it had previously engulfed a photosynthetic bacteria about 100 million years ago). There is a tendency for endosymbiotic organisms to lose function over time as their genes succumb to random mutations, since they are isolated from their free-living cousins. Paulinella solved this problem by engulfing other bacteria and taking their genes to replace the broken genes in their photosynthetic organelles.

“The major finding of the study is the microbial world, which we know is full of valuable genes, can move these genes between organisms according to need,” said Debashish Bhattacharya, a study co-author and distinguished professor in the Department of Ecology, Evolution and Natural Resources at Rutgers. “When a microbe has a gene deficit, it can in some cases fill that deficit by grabbing the same gene from the environment. This shows how fluid microbial genomes really are.”

Genes are more fluid in the microbial world, but they are also fluid in the macro world as well. Sweet potatoes have been found to have a gene acquired from soil bacteria about 8,000 years ago. All domestic sweet potato varieties examined to date have the bacterial genes, which likely helped the plants develop their enlarged and edible roots.

Bacteria are a different kingdom of life from plants. You cannot get more evolutionary distance than that. And yet the bacteria gene, transferred by nature without any human intervention, works just fine in the plant.


Our intuitions about nature do not seem to be accurate. This is broadly true – science has largely been the practice of disproving our intuitions about reality.

Our intuition tells us that species are very specific things unto themselves. Pre-evolutionary biologists certainly accepted this without question. That is why our creation myths talk about creating creatures each according to its own “kind.”

The reality is that species are fuzzy, they blend into each other. Life is messy, and all living things are related to each other. We also swap genes all the time.

Human, for whatever reason, evolved strong emotions and intuitions surrounding food. We tend, in fact, to be neurotic about food. This probably had an advantage when we had to find food in a hostile world of mostly poison. Now it leads to some strange behaviors, like the obsession of many children with keeping their food segregated on their plate.

The emotion of disgust is clearly adaptive, but emotions are blunt instruments. We like our food to be pure and pristine, uncontaminated, and wholesome. This is reasonable, but the problem comes when we try to operationally define what we mean by these things.

The “clean eating” and “natural” eating movement is largely based on a misapplication of the clumsy emotion of disgust and our inaccurate intuitions about nature. Putting a gene from one kingdom into another is not unnatural, and being natural does not mean anything anyway. Genes are being swapped all over the place. Genes do not contain the “essence” of the “species” to which they belong. Genes are just tools, they are instructions for assembling amino acids into proteins. Genes are promiscuous tools – they don’t care who they work for.

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