horizontal

Now, in bacteria — which are a type of prokaryote, or single-celled organism — a lot of evolution happens by horizontal gene transfer.

This isn’t necessarily good for us, though: antibiotic resistance has become a massive problem in large part due to horizontal transfer of genes from drug-resistant species into bacteria species that were once routinely killed by medications.

To simplify a bit, if Bacteria A acquires gene 1 by horizontal transfer and also acquires gene 2, and then we notice that Bacteria B has also acquired gene 1, we might correctly predict that Bacteria B has gene 2 as well — because in this scenario, genes 1 and 2 tend to stick together in a genome.

What this means is that evolution in E. coli, despite the serendipity of horizontal gene transfer, isn’t just a matter of chance.

Around her living room, miniature dioramas of crucial moments in Black American history took up much of the horizontal space.