Quammen is right that the horizontal transfer of genetic information does complicate our effort to understand the evolutionary past, but he goes too far in claiming that HGT essentially undermines any and all attempts to reconstruct the evolutionary past: “The tree of life is not a true categorical because the history of life just doesn’t resemble a tree.” Before accepting this radical conclusion, we must answer two questions: How in practice can horizontal genetic transmission occur, and how common is it?
In the end, Quammen provides us with a lucid guide to a lot of interesting science, but he overstates the impact of horizontal genetic transmission on our ability to reconstruct Darwin’s diversifying evolutionary tree. Today, that sketched-out tree of Darwin still looks good, even if, à la Quammen, we should add a couple of faint dashed lines showing HGT between its spreading branches. Jerry A. Coyne, “A challenge to Darwin’s branching view of evolution” at Washington Post (paywall)
The thing is, once the guardians of Darwin’s legacy have conceded that non-Darwinian evolution occurs, it is not their sole prerogative to decide whether and how it matters. Of course, they will pretend as long as they can that it is.
See also: At New York Times: Darwin skeptic Carl Woese “effectively founded a new branch of science” In fairness, many of us DID sense that the people splintering lecterns in favor of Darwin’s Tree of Life were more certain than the facts would turn out to warrant. Every so often, a new poll would announce, to general hand-wringing, that much of the public doesn’t “believe in” evolution. Most of us didn’t fight with anybody about it, we just waited… A world where horizontal gene transfer is a “thing,” (and epigenetics as well) actually makes a lot more sense from experience than the “selfish gene” world.
John Hawks is cool to epigenetics shedding light on evolution The assertion that natural selection can account for complex, detailed changes, given enough time, is a mantra: That is, if specific probability calculations render that unlikely, so much the worse for probability theory. Responses like this from a usually level-headed thinker mainly demonstrate that epigenetics is likely to upset quite a few applecarts.
Horizontal gene transfer: Sorry, Darwin, it’s not your evolution any more