Chimeras are for Real!

We know that genetic changes are transmitted “vertically”, i.e., from parent to child. But can genes be transmitted “horizontally”, i.e., between two unrelated strangers? Even better (or creepier), can genes be transmitted “horizontally” across species?

Most of our myths, world over, have imagined such chimeras, by cutting and pasting parts of different species. Sometimes they are monsters: think of the half-bull, half-man Minotaur of the Greeks. Sometimes they are cute: think mermaids. At other times, they’re God’s way of finding a way around a boon granted to an evil rakshasa: think Narasimha avatar.

Siddhartha Mukherjee, in his terrific book The Gene, says this question was explored in that “reliable barometer of American anxieties and fantasies – comic strips”! When a radioactive spider bit Peter Parker:

“The spider’s mutant genes are transmitted to Parker’s body presumably by horizontal transfer… thus endowing Parker with “agile and proportionate strength of an arachnid.”

Ta da! Thus was born Spiderman!

Unlike the stereotyped mutants-are-evil theme, Mukherjee points out that the X-Men comics “reversed the role of the victim and the victimizer”:

“In X-Men, the mutants were forced to run and hide from the terrifying tyranny of normalcy.”

But comics, movies, fairy tales and myths aside, is “horizontal” gene transfer even possible? Yes, it has been happening almost since the beginning of life! But not in the complex forms of life. As Ed Yong wrote in his awesome book, I Contain Multitudes:

“Bacteria have been carrying out these horizontal gene transfers, or HGT for short, for billions of years… It allows bacteria to evolve at blistering speeds. When they face new challenges, they don’t have to wait for the right mutations to slowly amass within their existing DNA. They can just borrow adaptations wholesale… If an innovative bacterium evolves one of these genetic tools, its neighbors can quickly obtain the same traits.”

Earlier, I said that HGT doesn’t happen across complex life forms. But how about HGT from bacteria to complex life form? Such cases have indeed been identified been found. The most extreme case, says Yong, is where all the genes of a bacteria were found to also be part of a Hawaiian fly:

“Everything that it was, the sum of its genetic identity, hopped over into the fly.”

Looks like the chimeras are everywhere. Since it has been happening at the tiniest of scales, we just didn’t see it for most of our history!