What Can 'DNA Barcodes' Tell Us About Evolution and Ourselves?
Sorting and defining species is a messy process. Dozens of methods exist and all have their benefits and drawbacks. Surely, taxonomy – the science of classifying organisms – would be so much easier if life forms came with barcodes…
Interestingly enough, there's actually something to that hopeful desire. Since the turn of the century, a group of scientists has attempted to classify species by sequencing their DNA, specifically DNA from a specific region inside mitochondria, the energy production centers of cells.
This 'DNA barcoding' doesn't work well for all forms of life, particularly plants, but it does work exceedingly well for animals. In a 2016 study, researchers used mitochondrial DNA to classify bird species then compared their results with those of traditional methods. The two classification systems agreed in 94% of cases. Strong levels of agreement have also been found for arthropods, mollusks, echinoderms, and chordates (which includes hominids).
Over the past decade, scientists have collected DNA barcodes from the mitochondria of five million specimens across 100,000 animal species. With this bounty of data, they can start cranking out some cool findings.
Researchers just published some fascinating factoids today to the journal Human Evolution. Mark Stoeckle, a Senior Research Associate at the Program for the Human Environment at Rockefeller University, and David Thaler, a geneticist at the University of Basel, poured through the data and discovered that the average difference in mitochondrial DNA between two humans is roughly 0.1 percent. In this respect, we are little different than most other species in the animal kingdom.
“If a Martian landed on Earth and met a flock of pigeons and a crowd of humans, one would not seem more diverse than the other according to the basic measure of mitochondrial DNA,” Jesse Ausubel, Director of the Program for the Human Environment at The Rockefeller University, said in a statement.
Stoeckle and Thaler also found that older species tended to have a greater average difference in mitochondrial DNA. This makes sense, as genetic adaptations tend to accumulate over time, which can lead groups of individuals within a species to diverge into entirely new species. When they do, their mitochondrial DNA is noticeably different.
“If individuals are stars, then species are galaxies. They are compact clusters in the vastness of empty sequence space,” Thaler analogized.
The study demonstrates that “Big Data” can play a pivotal role in classification, and has the potential to infuse taxonomy with a needed measure of objectivity.
Source: Stoeckle, M.Y. & Thaler, D.S. "Why should mitochondria define species?" HUMAN EVOLUTION Vol. 33 - n. 1-2 (1-30) - 2018. DOI: 10.14673/HE2018121037