Organism

Number of species depends how you count them

Hercules beetles
DRAWING LINES Scientists sometimes have difficulty determining whether organisms, such as these Hercules beetles, are members of different species. Genetic analysis alone may divide populations into species that don’t exist by other biological criteria.

Genetic methods for counting new species may be a little too good at their jobs, a new study suggests.

Computer programs that rely on genetic data alone split populations of organisms into five to 13 times as many species as actually exist, researchers report online January 30 in Proceedings of the National Academy of Sciences. These overestimates may muddy researchers’ views of how species evolve and undermine conservation efforts by claiming protections for species that don’t really exist, say computational evolutionary biologist Jeet Sukumaran and evolutionary biologist L. Lacey Knowles.

The lesson, says Knowles, “is that we shouldn’t use genetic data alone” to draw lines between species.

Scientists have historically used data about organisms’ ecological distribution, appearance and behavior to classify species. But the number of experts in taxonomy is dwindling, and researchers have turned increasingly to genetics to help them draw distinctions. Large genetic datasets and powerful computer programs can quickly sort out groups that have become or are in the process of becoming different species. That’s especially important in analyzing organisms for which scientists don’t have much ecological data, such as insects in remote locations or recently extinct organisms.

Knowles and Sukumaran, both of the University of Michigan in Ann Arbor, examined a commonly used computer analysis method, called multispecies coalescent, which picks out genetic differences among individuals that have arisen recently in evolutionary time. Such differences could indicate that a population of organisms is becoming a separate species. The researchers used a set of known species and tested the program’s ability to correctly predict…

The Weird Event That Led to You and Ewe and Yew

Life arose on earth over three billion years ago, and for a long time, there were only one-celled organisms. These prokaryotes diverged and evolved in many ways, but making the leap from one cell to many cells (eukaryotes) was a paradigm shift that led to every living thing on earth that’s big enough for us to see -including us. How did that happen? Before we could sequence genes, the prevailing theory was a gradual development as cells mutated, diverged, and evolved. However, recent genetic research has led credence to the idea that the first two-celled organism was a merger that only happened once.

The alternative—let’s call it the “sudden-origin” camp—is very different. It dispenses with slow, Darwinian progress and says that eukaryotes were born through the abrupt and dramatic union of two prokaryotes. One was a bacterium. The other was part of the other great lineage of prokaryotes: the archaea. (More about them later.) These two microbes look superficially alike, but they are as different in their biochemistry as PCs…