Jumping Genes

When we think about who we are—our appearance, our susceptibility to diseases, and many other of our characteristics—we tend to think about our parents. We've inherited most of our traits from them, which they in turn got from their parents. That's the way evolution works. The key process is that when DNA is reproduced, tiny errors may happen, and those errors get passed down the hereditary path. If the errors are beneficial, those who possess them are more likely to survive than those who don't, and so those genes pass on the fortunate error. This is the essence of “survival of the fittest.”

So, our genetic makeup comes to each of us in this manner: from parent to child; and the child later becomes a parent and passes those genes on to their children. Our genome is mostly species specific.

Now, in addition, we do share many of our genes with the chimpanzees, because we and they have a common ancestor that lived some seven million years ago, who passed its genes to both of our species. In fact, we have about a 98% overlap with chimps. But don't we also share a few genes with cows and mice (other mammals), as well as with birds and even lizards? Don't we even share a few genes with trees and mushrooms? Yes, but again, it's simply because all life on Earth descends from the “first ancestor,” which passed on its genes to all of us.

Thus, even though we share a number of genes with other species, most of us have come to understand the story of our personal genes coming primarily through inheritance from our parents. But as so often happens in science, the accepted stories periodically become corrected and updated; a new story emerges—an improved theory comes to light.

Out of research at the University of Adelaide in Australia comes a recent update on the gene inheritance story: it seems that a portion of our genes do not come from mom and pop, but from what's termed a “horizontal transfer” of genes between significantly different species. These “jumping genes” are dubbed “retrotransposons.” The Adelaide scientists traced two particular genes across more than 700 species of plants, animals, and fungi. They found this particular pair of genes appeared repeatedly—and they also verified that these genes were not inherited from parents, but had entered the organisms, after birth, as foreign DNA.

These foreign genes behave sort of like a parasite—in that they can disrupt normal genes. In fact, the researchers conclude that retrotransposons have been a key driver in the rapid evolution of mammals over the past 100 million years. After the dinosaurs disappeared 65 million years ago, the tiny, ineffective mammals who survived were ready to rapidly evolve...and subsequently came to dominate the planet.

How do some genes jump from one kind of species to another very different species? How does a gene from a dandelion become a part of the genome of a human? As yet, the mechanism remains a mystery. Scientists theorize that the horizontal transfer process may be caused by ticks, mosquitoes, leeches, locusts, and viruses. Even bedbugs! Yikes!

Fascinating! This development raises a few crucial questions: Am I related to my tomatoes? Am I committing a crime—or even cannibalism, when I eat french fries? Am I a monkey's uncle? That last one plays upon my Mom's expression of mild disbelief in something, when she'd utter, “Well, I'll be a monkey's uncle.” I used to laugh, because she couldn't be anybody's uncle, but now I perceive a new slant on that old expression, thanks to jumping genes.