Lest the next 700 words put you to sleep, the punchline: pretty much every organism – from the lowly bacterium, to the sweet potato, on up to Homo sapiens – is genetically modified; every species trades genes asexually with other species. If you’d like to define your food supply by the purity of its genome, you might look into caloric restriction… and I mean total restriction, since purity is a fantasy.
Nothing is simple. Not even a label like “this is a GMO product”. In fact, such labels – imparting a sense of security – can actually dull our senses and make us vulnerable to other, bigger scary monsters the celebrities and life-style advisors never opined about.
So life is not an easy process encapsulated by safe-sounding descriptors. And most definitely evolution is not simple. This story isn’t going to make the grocery store choices easier, even if you shop at the most expensive boutique produce stands. Because your notion of ‘natural’ is wrong.
Before some Food Dipshit suggests it, I’d like to make clear that I’m not an apologist for industry, though as a professor with 2 kids and a mountain of southern Californian mortgage debt, I might be willing to be their shill if they would pay for my new timing belt. Are you listening, Monsanto?
But to get it out of the way: there are plenty of legitimate concerns about genetically modified foods, whether they be cis-genic or trans-genic. Those are not really what I’m interested in today, but they wind together the social and corporate good in a kind of technological caduceus, with twin snakes nipping constantly at the hand of humanity holding it. If you’re into dense(r) science treatises, I direct you to the Union of Concerned Scientists, but I hasten to add that acknowledging the evils of GMO crops pollinating ‘natural’ crops – while real enough – does not excuse us from actually understanding what we revile. In any case, I’m not going to write about GMO crops in particular in this post, but you can read some of my preliminary thoughts elsewhere.
As a science educator, my goal is to show people the tools they need inform their decisions with evidence. To that end I want to present a notion to you, one for which there is quite a bit of evidence. It’s not always simple, and it doesn’t parse into sound bytes, but it is beautiful and awe-inspiring in the truest sense.
Take the emerald sea slug, Elysia chlorotica. The first thing you notice is that it’s adapted to look like a leaf, a sort of camouflage that I suppose keeps the sea turtles at bay. But what’s really cool is that this animal steals chloroplasts from the algae it lives on, integrating these organelles into its own body and using them for photosynthetic sugar production for months after their original owners, um, donated them. This in itself could be an early glimpse of symbiogenesis, the process by which complex life created itself from simpler building blocks. In time, we could imagine Elysia doing more than hijacking algal structures, and instead taking ownership of the substructures (genes) that would allow it to make its own chloroplasts… then it’ll more organically resemble the sugar and oxygen-producing leaf that it already mimics.
As great as that symbiogenesis story is, though, Elysia brings us back to the terms ‘GMO’, ‘natural’, and ‘pure’. In fact, algal genes have already been found incorporated into the genome of the slug. Whatever role those foreign genes may eventually play in native photosynthesis in an animal, what we can say now is that – through a totally ‘natural’ process – Elysia has become a transgenic organism, incorporating genes from the Plant Kingdom into its own genome in a stable, permanent way. It is a GMO, and it turned into a GMO just by eating. Is it an abomination? Is it dangerous? Should we turn away from it?
Un/fortunately, we can’t really turn away from it, even if we wanted to. Because when we do, we will simply bump into another example of natural GMOs, and another, and another. The phenomenon Elysia demonstrates is called ‘Horizontal Gene Transfer’, or HGT, and it seems to be pervasive characteristic of DNA-based life (which is to say all terrestrial life). It’s horizontal, because the transfer of genetic information jumps from one branch of the tree of life to another. Usually – let’s say according to the Standard Model – genetic traits are passed down through descent. That’s a really powerful model, because it allows us to build wonderfully detailed maps, called phylogenetic trees, that reveal the relationships between all life forms; those relationships are the most beautiful story ever told, but that’s for another day. At the level of the slug, Elysia’s algally-derived genes – and so many other horizontal gene transfer events – upend that model, or at least force us to add another layer to our understanding. And adding complexity to my understanding of nature always feels good and right.
In the bacterial world, horizontal gene transfer is very, very common. But there are plenty of examples of HGT in our own genome, and the best is probably the retrovirus. Every time a retrovirus invades one of your cells, it finds a way to insert its genome into your own. Now, most of the time, infected cells are killed and eliminated, along with the viral DNA, so the new information doesn’t persist. But if the viral genome finds its way into a germline cell, and eventually into a sperm or an egg, then it has just become a permanent component of your genetic heritage (if you survive long enough to procreate).
What’s more, that virus might be carrying along a fragment of a previous host’s genome! The transfer event could bring along a packet of DNA from multiple organisms. Gene upon gene upon gene, and the virus might be considered a tool of its previous host, helping revive those dead genes. And the story gets another layer.
In fact, the human genome is replete with viral remnants, which account for more of our genome than actual genes do. I’m being careful with my adjective here, to avoid making these thousands of viral genome bits sound like ‘junk’; the word is not yet in as to the extent to which they have come to serve some functional role in our genome, and that’s not my task here. But there’s so much to the story of these ‘endogenous’ viruses, and lest they distract us too much: YOU ARE A VIRAL GMO.
We can take a step back and look more holistically at nonanthropogenic GMOs (horizontal gene transfer events). Although the original study of the human genome suggested HGT was rare, more recent work suggests otherwise. Leaving aside viral detritus, it now seems that the human genome is possessed of no less than 145 genes from other organisms. That’s fewer than 1% of our genes, to be sure, but it’s not a small number; we’re pretty heavily modified. It’s notable that most of these genes come from simple organisms, bacteria and protists. The human microbiome is another story, but let’s just say it’s pretty widely accepted that HGT mostly occurs between organisms with a long history of interaction. While none of our foreign genes come from other animals, 5 or 10 of our genes originated in plants… apparently Elysia isn’t the first animal to borrow from our green brethren. And isn’t it fun to think that, while we mostly worry about how we are modifying plant genomes, they’ve actually been modifying us for millions of years?
It’s important to note, too, that these foreign genes are not just gathering dust; it seems they have been actively recruited into crucial functions. One particularly fun plant gene, now working away in our genome, encodes a protein called Hephaestin – after the blacksmith son of Zeus and Hera – since it helps mobilize dietary iron. Within genomes, recruitment of one gene to a new purpose is pretty standard; but isn’t it beautiful to imagine ‘invading’ genes being turned to useful ends in their new locus?
Returning to endogenous retroviruses, that insertion of a new gene in an existing framework could cause problems is pretty intuitive. And problems fit well into the ‘Dangers of GMOs’ narrative. Dropping in on working genes can inactivate them, resulting in a whole host of diseases. But there are many examples of how foreign genes have become wholly integral to human biology, as well.
A favorite of mine is HERV-W (Human Endogenous RetroVirus-W) that is only activated in human placenta. The retrovirus has bequeathed us a gene that encodes the protein syncytin. Originally (the virus that became HERV-W infected us >25 million years ago), syncytin was an envelope protein, providing the virus with its protective sheath. Since then, however, syncytin has been recruited to perform a fundamentally important job in humans: formation of the placenta. What could be more essential than reproduction? Even cooler is to think that viral envelope proteins, which encapsulate viral genomes, can be repurposed to fuse human membranes to form the placental syncytium, encapsulating embryos instead. What power! No only did we survive a plague 25 million years ago, but the survivors reshaped the monster into the most beautiful of seashells.
To bring this train into the station: it is my sincere hope that a deep understanding of a problem helps us turn our right intention into right action. In order to understand the meaning of the lightning rod term ‘GMO’, and not just irrationally react to it, we need to learn about just how common the cross-species sharing of genes actually is. I’d like to see the fear and ignorance replaced with with wonder at nature’s beautiful mess. The bitter pill is that losing our ignorance means learning some molecular biology, or wait… maybe that’s the spoonful of sugar!