Searching but not finding
We’re lost in this masquerade
— Leon Russell, This Masquerade
A costume party can be a lot of fun, but for those entangled in a masquerade little enjoyment exists when the truth is obscured.
Evolutionary biologists who study pieces of DNA called transposons have discovered that these sequence elements
are involved in their own masquerade. These bits of DNA move within the genome of an organism. Recently, however, biologists have discovered that transposons can also move from the genome of one organism into that of another.1 And it’s no party for evolutionary biologists when this happens. The ability of transposons to jump around creates confusion, subverting the most commonly cited evidence for biological evolution.
In recent years, evolutionary biologists have increasingly used DNA sequences to construct evolutionary trees. Researchers find transposons particularly suitable for this endeavor. When evolutionary biologists propose evolutionary relationships, they rely on the principle that organisms with shared DNA sequences arise from a common ancestor.
But other mechanisms exist that can introduce the identical DNA sequences. Horizontal gene transfer (HGT) is one.
Horizontal Gene Transfer Mimics Common Ancestry
HGT refers to any process that transfers genetic material to another organism without the recipient being the offspring of the donor. HGT occurs frequently in bacteria and archaea. A consequence of this process is that, from an evolutionary vantage point, microbes that are unrelated through common descent will possess the same DNA sequences. In other words, HGT has the same genetic signature as common ancestry.
Until recently, most biologists thought that HGT was confined to microbes. Yet, in the last couple of years, researchers have uncovered evidence for horizontal gene transfer in higher plants and animals, which they think is mediated by viruses and single-celled pathogens transmitted from species to species via an insect vector. Because of transposons’ mobility within genomes, they readily take part in HGT events.
As with microbes, HGT in higher plants and animals obfuscates the ability of evolutionary biologists to use transposons to establish reliable evolutionary relationships. For example, researchers discovered that when they use two different classes of transposons, called BovB and Spin elements, to build evolutionary trees, absurd relationships resulted. Cows were more closely related to snakes than to elephants and geckos more closely related to horses than to other lizards.
Many people regard shared DNA sequences as the best evidence for evolution and common descent. But as this cutting-edge research demonstrates, other mechanisms, such as horizontal gene transfer, can introduce the same DNA sequences in organisms, thus, masquerading as evidence for common descent. As science continues to unmask understanding of these processes, the case for common design strengthens.
- John K. Pace II et al., “Repeated Horizontal Transfer of a DNA Transposon in Mammals and Other Tetrapods,” Proceedings of the National Academy of Sciences, USA 105 (November 4, 2008): 17023–28; Ali Morton Walsh et al., “Widespread Horizontal Transfer of Retrotransposons,” Proceedings of the National Academy of Sciences, USA 110 (January 15, 2013): 1012–16.