Key Concepts

• Formal taxonomic systems first identified species based on visual traits such as fins or fur. Later, the species concept changed, specifying that two organisms should be capable of breeding.
• Today biological diversity can be ascertained by sampling DNA and tracking how a species descended from a common ancestor.
• The debate over species definition is far from over and is more than a mere academic spat. Proper classification is essential for designating the endangered list.

If you visit Algonquin Provincial Park in Ontario, you may hear the high, lonesome howls of wolves. You may even be lucky enough to catch a glimpse of a distant pack racing through the forests. But when you show off your blurry pictures back home, what species should you boast that you saw? Depending on the scientist you ask, you may get a different answer. Some may even offer you a few different answers all at once.

In the 18th century European naturalists dubbed the wolves of Canada and the eastern U.S. Canis lycaon, because they seemed distinct from Canis lupus, the gray wolf of Europe and Asia. By the early 1900s North American naturalists had decided that they were actually gray wolves as well. But in the past few years Canadian researchers who have analyzed wolf DNA have come full circle. They argue that gray wolves only live in western North America. The wolves of Algonquin Provincial Park belong to a separate species, which they want to call C. lycaon once more.

Other wolf experts do not think there is enough evidence to split C. lupus into two species. And both sides agree that the identity of the Algonquin wolves has become far more murky thanks to interbreeding. Coyotes (another species in the genus Canis) have expanded east and begun to interbreed with C. lycaon. Now a sizable fraction of these eastern coyotes carry wolf DNA, and vice versa. Meanwhile C. lycaon has been interbreeding with gray wolves at the western border of its range. So the Algonquin animals are not just mixing C. lycaon DNA with C. lupus DNA—they are passing on coyote DNA as well.

Even if C. lycaon was once a species, is it a species anymore? Many researchers find that the best way to think of a species is as a population whose members breed mostly among themselves, making the group genetically distinct from other species. When it comes to wolves and coyotes, it is hard to say quite where one species stops and another starts. “We like to call it Canis soup,” says Bradley White of Trent University in Ontario.

The debate is about much more than naming rights. Wolves in the southeastern U.S. are considered a separate species, the red wolf (Canis rufus). This wolf has been the subject of an enormous project to save it from extinction, with a captive breeding effort and a program to reintroduce it to the wild. But the Canadian scientists argue that the red wolf is really just an isolated southern population of C. lycaon. If that is true, then the government has not in fact been saving a species from extinction. Thousands of animals belonging to the same species are still thriving in Canada.

As the case of the Algonquin wolves demonstrates, defining species can have a huge effect on whether an endangered group gets protected and whether a habitat is saved or lost. “In one sense, it’s a very esoteric subject, but in another, it’s a very practical issue,” says Alan Templeton of Washington University in St. Louis, “even a legal issue.”

An Embarrassment of Definitions
It may come as a surprise to see scientists struggling to agree on something so basic as how to decide that a group of organisms form a species. Perhaps it is the Latin that gives species names the whiff of absolute certainty and that has misled the public into thinking the rules are simple. Perhaps it is the 1.8 million species that scientists have named in the past few centuries. Perhaps it is laws like the Endangered Species Act, which take for granted that we know what species are. But in fact, the very concept of species has fueled debates for decades. “There is no general agreement among biologists on what species are,” says Jonathon Marshall, a biologist at Southern Utah University. At last count, there were at least 26 published concepts in circulation.