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In a recent paper in PNAS, you reveal evidence that, among bacteria, horizontal gene transfer events are not indiscriminate – that “the observed phylogenetic central tendency observed in genome analyses seems to be caused by two processes: shared ancestry and biased horizontal gene transfer (HGT).” Before I read this, I thought that HGT would seem, on the surface, to undermine vertical inheritance. Do you think horizontal gene transfer can actually bolster speciation?
Yes, and I think so for several reasons. One is that if an organism acquires a new gene that allows it to adapt to a new environment, and all the descendants of this organism inherit this gene, then the presence of this transferred gene becomes a perfect character for this group of organisms that descended from this ancestor. The other reason that gene transfer is not as detrimental as people usually think it is, is that it is not between randomly selected organisms. Often it occurs between very closely related organisms – but because most genes are traded between closely related organisms, the closely related organisms appear to be even more closely related. The gene transfer reinforces the similarity due to shared ancestry.
I understand that for a long time you advocated for recognizing the importance of horizontal gene transfer in microbial evolution, but you were in the minority. Whole genome sequencing has since revealed that HGT is rampant among microbes, particularly among related strains. Do you feel vindicated by these discoveries?
Not really – but it feels nice to get recognized for things I said 17 years ago. The pendulum is swinging back and forth. In the 50’s, 60’s, and 70’s, people were giving up on doing the phylogeny of microorganisms because they recognized that genes can be transferred, and with the use of rRNA as a license plate to trace microbes [in the 80’s], everything changed and it became possible to trace evolutionary history. And now the pendulum is swinging back, and we see that if you really want to see the evolutionary history of organisms you need to take both into account – vertical inheritance and the acquisition of new genetic material.
In the U.S., roughly 25% of the population does not accept the theory of evolution. As someone whose work relies on a sophisticated understanding of evolution, do you feel any responsibility for educating the public or advocating for the benefits of the scientific method?
I think it is really important to educate the public about the scientific method and the evidence for evolution. It is sad that a large section of the population, for unscientific reasons, reject the idea of evolution – that leads to a very narrow understanding of nature. I think it is possible to reconcile religion and the fact that evolution is occurring.
Where do you see your field in 10 years?
I think we will have a much better understanding of how metabolic pathways and the cellular machinery were put together in the evolutionary process. I think many biologists still see the cell machinery as a static, non-changing entity and I think the consideration of evolution will provide a much richer picture of how metabolism and metabolic pathways and features have come together. And I would hope that this understanding can be extended back to the early evolution of life.
If you had to change careers today and you could do anything, what would you do?
I might become a painter – that would be one possibility. Or I might go back into mathematics, dynamic systems. That would be more difficult to get back into.
What’s your favorite science book?
The obvious choice is the Origin of Species–it’s a really worthwhile book.
What is something about you that most people don’t know?
One of the things many people don’t realize is that I started my career as a plant physiologist, doing transport physiology of plants. And I’m also interested in dynamic systems, things like fractals. And I have an interest in non-linear dynamic systems.