Darwinian evolution [is] the transmission of genes and traits down the family line. DNA, it turns out, can also be passed laterally, between individuals, including those of different species. This discovery represented a tectonic shift in our understanding of nature, a story that David Quammen tells wonderfully in his exhaustively researched book, Tangled Tree: A Radical New History of Life.

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Darwinian evolution, of course, can explain the rise of antibiotic-resistant bugs. It happens like this. A colony of bacteria gets doused in a deadly antibiotic. Amidst the die off, one bacterium has a lucky mutation that, say, lets it manufacture a molecule that can pump the antibiotic safely out of its cytoplasm into the surrounding slime. That lucky guy thrives and divides and replaces its massacred brethren.

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But unfortunately for us (and unknown to Darwin), bacteria possess another means to acquire antibiotic resistance without having to sit around waiting for the next lucky mutation: They can swap genes the way we share recipes. When one bacterium rolls up close to another—not necessarily even of the same species—it can share a chromosome containing a slew of genes with, say, an enzyme that can smash penicillin into pieces.

Horizontal gene transfer is much more than a way for bacteria to share antibiotic resistance genes; it happens throughout nature and in the history of living things.

Read full, original post: How Scientists Discovered Extra Steps in Evolution