(p. D1) Naturalists have been trying for centuries to catalog all of the species on Earth, and the effort remains one of the great unfinished jobs in science. So far, researchers have named about 2.3 million species, but there are millions — perhaps even billions — left to be discovered.
As if this quest isn’t hard enough, biologists cannot agree on what a species is. A 2021 survey found that practicing biologists used 16 different approaches to categorizing species. Any two of the scientists picked at random were overwhelmingly likely to use different ones.
“Everyone uses the term, but no one knows what it is,” said Michal Grabowski, a biologist at the University of Lodz in Poland.
The debate over species is more than an academic pastime. In the current extinction crisis, scientists urgently need to take stock of the world’s biological diversity.
. . .
(p. D4) As scientists gather more genetic data, fresh questions are emerging about what seem, on the surface, to be obviously separate species.
You don’t have to be a mammalogist to understand that polar bears and brown bears are different. Just one look at their white and brown coats will do.
The difference in their colors is the result of their ecological adaptations. White polar bears blend into their Arctic habitats, where they hunt for seals and other prey. Brown bears adapted for life on land further south. The differences are so distinct that paleontologists can distinguish fossils of the two species going back hundreds of thousands of years.
And yet the DNA inside those ancient bones is revealing an astonishing history of interbreeding between polar bears and brown bears. After the two lineages split about half a million years ago, they exchanged DNA for thousands of years. They then became more distinct, but about 120,000 years ago they underwent another extraordinary exchange of genes.
Between 25,000 and 10,000 years ago, the bears interbred in several parts of their range. The exchanges have left a significant imprint on bears today: About 10 percent of the DNA in brown bears comes from polar bears.
Beth Shapiro, a paleogeneticist at the University of California, Santa Cruz, said that the interbreeding most likely occurred when swings in the climate forced polar bears down from the Arctic and into brown bear territory.
For the full story see:
(Note: ellipsis added.)
(Note: the online version of the story has the date February 19, 2024, and has the title “What Is a Species, Anyway?”)
The 2021 survey mentioned above was more fully detailed in: