There was an interesting article about Charles Darwin in Smithsonian Magazine recently that mentioned something that I found really interesting, and surprising. In addition to inherited genetics, genes can also be passed between other individuals, even between those of a different species. Animals, including humans, don’t usually gain whole genes in this manner, but our DNA is full of smaller pieces of genetic material that we received from various viruses throughout our evolutionary history. This includes much material that is responsible for deciding when genes are active or dormant. Apparently this horizontal transfer of genetic material is quite common in bacteria, being how antibiotic resistance spreads from one strain of bacteria to another.
Elsewhere in the same issue of the magazine was a great example of this phenomenon. A sea slug, Elysia chlorotica, contains chloroplasts that it extracts from the algae that it eats. It is the first animal to have gained at least one gene necessary for photosynthesis, from these algae, and it can photosynthesize for months on its own.
