Some of my favorite commercials are part of the “Don’t Judge Too Quickly” series.
The moral of these commercials: things aren’t necessarily what they seem.
The same could be said about the scientific case for common ancestry. Though the evidence seems compelling, a number of new discoveries should caution us not to judge too quickly. Adding to these recent advances is work by a team of researchers from the University of Texas, Arlington.1 (Go here, here, and here for some recent articles on the misleading evidence for common ancestry.)
The Case for Common Ancestry
According to the evolutionary paradigm, all life on Earth is related through the process of common descent. The idea is this: in the distant past, an organism (or community of organisms) called the last universal common ancestor spawned a number of lineages that evolved separately, and in turn, diverged, etc. to ultimately generate the diversity of life that exists today and has existed throughout Earth’s history.
Evolutionary biologists spend significant effort to piece together the presumed evolutionary history of life. To do this, they build evolutionary trees—diagrams that putatively describe the ancestral and descendent relationships of Earth’s life displayed in a branching tree-like pattern. These scientists employ a number of different approaches to construct evolutionary trees. For example, they use anatomical similarities and differences to discern, what they believe to be, evolutionary relationships. Organisms that display a high degree of similarity are interpreted to share an ancestor in the more recent past than those with few features in common.
As a corollary to this idea, evolutionary biologists interpret shared similarities among organisms as evidence for their common ancestry, with differences arising after the two lineages diverged from one another.
Over the last decade or so, evolutionary biologists have increasingly turned to DNA sequences to construct evolutionary trees. As with anatomical features, organisms with highly similar DNA sequences are viewed to have shared a common ancestor more recently than organisms that display greater differences. Evolutionary biologists also interpret genetic similarities among organisms as evidence for common ancestry, with differences arising post-divergence.
Horizontal Gene Transfer Mimics Common Ancestry
New work by scientists from UT Arlington complicates the interpretation of DNA sequence similarity among organisms. These scientists discovered that horizontal gene transfer mediated by parasites could generate the same genetic signature as common ancestry by transferring DNA sequence elements (called transposons) among organisms.
Horizontal gene transfer refers to any mechanism that transfers genetic material from one organism to another, without the recipient being the offspring of the donor. Because of horizontal gene transfer (when viewed from an evolutionary standpoint), organisms unrelated by common descent will share the same DNA sequences.
Transposable elements, or transposons, are pieces of DNA with the capacity to move around organisms’ genome. There are three types of transposable elements:
- class 1 elements make copies of themselves and the copies then insert into another location within the genome;
- class 2 elements directly move from one location in the genome to another;
- retroviruses are infectious agents that insert themselves into organisms’ genomes.
Researchers long thought that the insertion of transposable elements into the genome took place at random locations, but recent work, including the efforts of the UT Arlington scientists, indicate that transposon insertion events are repeatable.
These reproducible insertion events and the mobility of transposable elements help explain why flatworms, insects, mollusks, amphibians, reptiles, birds, and mammals share several distinct classes of these DNA sequence elements. Based on their distribution in these animals, it appears as if the shared transposons were transferred from animal to animal via parasites. The occurrence of the transposons in a snail and an insect both known to transmit parasites from host to host supports this idea.
Horizontal Gene Transfer and the Case for Biological Evolution
Many people regard shared DNA sequences as the best evidence for evolution and common descent. But, as this recent work from UT Arlington demonstrates (along with other studies), there are other mechanisms beside common ancestry that can introduce the same DNA sequences in organisms unrelated via common descent.
These types of studies indicate that evolution’s best evidence may not support it at all. Horizontal gene transfer could be a consequence of some other type of mechanism, like parasite-mediation. It is interesting to note that the same transposons appear in tarsiers and squirrel monkeys and in bushbabies and lemurs, respectively—animals thought to be related to each other from an evolutionary perspective. On the other hand, the shared DNA sequences may actually point to something beyond natural mechanism as the explanation for features shared among organisms.
Common Ancestry or Common Design
If life stems from the work of a Creator, then shared features, including similar DNA sequences, will not reflect common descent but common design elements employed by that Creator. It is interesting to note that recent work has demonstrated that transposons play a functional role in the genome. (Go here for a recent article I wrote about the utility of transposons.)
Instead of explaining shared genes as a consequence of horizontal gene transfer via a natural process, they could be understood as originating by a Creator’s hand. In fact, genetic engineering, in which researchers (i.e., intelligent agents) introduce genes into the genomes of organisms in the lab, is also known as artificial horizontal gene transfer.
When it comes to the case for common descent, don’t judge too quickly. I won’t.
- Clement Gilbert et al., “A Role for Host-Parasite Interactions in the Horizontal Transfer of Transposons across Phyla,” Nature 464 (2010): 1347–50.