Really, it’s harder than you think. Individual science papers typically build on a larger body of knowledge and don’t stand alone; it is assumed that the reader has significant amounts of training in the subject at hand so that the authors don’t bother to fill in all the background. When writing a summary of the article for a general audience, one has to provide a lot of context, without simply reiterating the contents of, for instance, a molecular biology textbook and a year’s worth of upper level biology education. And if someone writing a summary of an article lacks that knowledge altogether, the misinterpretations can be disastrously wrong.
Take this article in TechTimes, Massive Genetic Study Reveals 90 Percent Of Earth’s Animals Appeared At The Same Time. The title alone is creationist clickbait, and the author of the story clearly didn’t understand the article at all. She gets it all wrong.
Landmark new research that involves analyzing millions of DNA barcodes has debunked much about what we know today about the evolution of species.
In a massive genetic study, senior research associate at the Program for the Human Environment at Rockefeller University Mark Stoeckle and University of Basel geneticist David Thaler discovered that virtually 90 percent of all animals on Earth appeared at right around the same time.
More specifically, they found out that 9 out of 10 animal species on the planet came to being at the same time as humans did some 100,000 to 200,000 years ago.
No, it didn’t. The paper says nothing of the kind.
The paper is an analysis of DNA barcodes. DNA barcoding is a process that uses a short stretch of mitochondrial DNA to map an individual organism to a species — it’s a technique that lets you look at a sample of a few cells, amplify and sequence a single gene (COI or COX1 are commonly used in animals), and then unambiguously identify the specific species those cells came from. Being able to do this relies on an interesting property of a species: there is limited variance in the barcode sequence within the species, but there has to be greater variance of that sequence from other, even closely related species. In other words, DNA barcodes form tight little clusters of similarity that correlate well with other criteria for defining a species.
That raises questions. You can read the original article, Why should mitochondria define species?, for yourself and see. The question is about why variations within a species should cluster so tightly. Stoeckle and Thaler propose a couple of hypotheses to explain that phenomenon.
Either 1) COI barcode clusters represent species-specific adaptations, OR 2) extant populations have recently passed through diversity-reducing regimes whose consequences for sequence diversity are indistinguishable from clonal bottlenecks.
It’s a meaty paper that goes through the evidence for both of those hypotheses, and I’m wishing I’d seen this paper last semester, when I was teaching evolutionary biology — there is a lot of useful evolutionary thinking going on here. Maybe I can revoke all of my students’ degrees and tell them they have to come back for one last thing? I think we can go through the paper adequately in about a week, so I’m sure they won’t mind.
Their final conclusion, after analyzing millions of barcodes, is fairly straightforward, I think.
The simple hypothesis is that the same explanation offered for the sequence variation found among modern humans applies equally to the modern populations of essentially all other animal species. Namely that the extant population, no matter what its current size or similarity to fossils of any age, has expanded from mitochondrial uniformity within the past 200,000 years.
This is not saying that there was a single instant in the last 200,000 years from which all modern species arose simultaneously. It’s a statement about the process of speciation: species arise from isolation of a limited subset of an existing population, which is why they have limited variation in their DNA barcodes, followed by an expansion of the new species’ population, during which the DNA barcodes accumulate variation slowly.
No, they did not find out “that 9 out of 10 animal species on the planet came to being at the same time as humans did some 100,000 to 200,000 years ago”. New species arise continuously, but they do so by going through a population bottleneck in geologically recent times. Homo sapiens arose as a distinct species between 100,000 and 200,000 years ago, but that notorious London Underground mosquito may have evolved in the 18th century…which is still within the past 200,000 years, you may notice.
It’s a bit like reading a statement that almost all people are less than 100 years old, and then wondering, publicly and in print, about what happened in 1918 to cause every human being on Earth to have been suddenly born in that year. That must have been some orgy to celebrate the end of the Great War.