We humans are a promiscuous and unchoosy species, and apparently we encourage such tendencies in the species forced to deal with us. Moises Velasquez-Manoff, reporting for the NYTimes:
In New England today, trees cover more land than they have at any time since the colonial era. Roughly 80 percent of the region is now forested, compared with just 30 percent in the late 19th century. Moose and turkey again roam the backwoods. Beavers, long ago driven from the area by trappers seeking pelts, once more dam streams. White-tailed deer are so numerous that they are often considered pests. And an unlikely predator has crept back into the woods, too: what some have called the coywolf. It is both old and new — roughly one-quarter wolf and two-thirds coyote, with the rest being dog.
The animal comes from an area above the Great Lakes, where wolves and coyotes live — and sometimes breed — together. At one end of this canid continuum, there are wolves with coyote genes in their makeup; at the other, there are coyotes with wolf genes. Another source of genetic ingredients comes from farther north, where the gray wolf, a migrant species originally from Eurasia, resides. “We call it canis soup,” says Bradley White, a scientist at Trent University in Peterborough, Ontario, referring to the wolf-coyote hybrid population.
The creation story White and his colleagues have pieced together begins during European colonization, when the Eastern wolf was hunted and poisoned out of existence in its native Northeast. A remnant population — “loyalists” is how White refers to them — migrated to Canada. At the same time, coyotes, native to the Great Plains, began pushing eastward and mated with the refugee wolves. Their descendants in turn bred with coyotes and dogs. The result has been a creature with enough strength to hunt the abundant woodland deer, which it followed into the recovering Eastern forests. Coywolves, or Eastern coyotes, as White prefers to call them, have since pushed south to Virginia and east to Newfoundland. The Eastern coyote is a study in the balancing act required to survive as a medium-size predator in a landscape full of people. It can be as much as 40 percent larger than the Western coyote, with powerful wolflike jaws; it has also inherited the wolf’s more social nature, which allows for pack hunting. (In 2009, a pack of Eastern coyotes attacked and killed a 19-year-old Canadian folk singer named Taylor Mitchell in Cape Breton, Nova Scotia.) But it shares with coyotes, some 2,000 of which live within Chicago’s city limits, a remarkable ability to thrive in humanized landscapes….
Thus did humans inadvertently create an ecological niche for a predator in one of the most densely populated regions of the country. In an exceedingly brief period, coyote, wolf and dog genes have been remixed into something new: a predator adapted to a landscape teeming with both prey and another apex predator, us. And this mongrel continues to evolve. Javier Monzon, an evolutionary biologist at Stony Brook University, has found that Eastern coyotes living in areas with the highest densities of deer also carry the greatest number of wolf genes. Another scholar of the Eastern coyote — Roland Kays, a zoologist at the North Carolina Museum of Natural Sciences in Raleigh — estimates that the Eastern coyote’s hybrid ancestry has allowed it to expand its range five times as fast as nonhybrid coyotes could have. In the urbanized Northeast, of all places, an abundance of large prey seems to have promoted a predator whose exceptional adaptability has derived, in large part, from the hodgepodge nature of its genome…
The emergence of the Eastern coyote, however, shows how human activity can break down the barriers that separate species. Perhaps the most obvious way in which humanity is altering the natural world is through climate change. The Arctic, where its effects are especially evident, is warming between two and four times as fast as the rest of the planet. Spring thaws now arrive weeks earlier; winter freezes come weeks later. Shrubs are invading once-barren tundra. Animals at high latitudes — where related species tend to have diverged more recently and can therefore interbreed more easily — are shifting their ranges in response to rising temperatures and melting sea ice. As they do, they may encounter cousins and hybridize.
In Maine, Minnesota and New Brunswick, Canadian lynx have lately produced cubs with the more southerly bobcat. A Southern flying squirrel has pushed north into southern Ontario and begun mating with its larger, boreal cousin. The best-known examples of this process are the polar bear-grizzly hybrids, sometimes referred to as grolar or pizzly bears, four of which have been shot by hunters in recent years; genetic testing indicated that one of them was a second-generation animal. There have been several other sightings of bears suspected of being hybrids, and this spring a mother thought to be one, accompanied by grizzly-looking cubs, was captured (tests are pending). Better management of grizzly hunting may have also contributed to this mixing by enabling males to advance into polar-bear country. “A warming Arctic is not a bad thing for grizzly bears,” says Andrew Derocher, a biologist at the University of Alberta.
We might regard these developments as unintended consequences of intensifying human activity on the planet. Yet in the past decade or so, scientists have discovered that the genomes of many species — far more than previously thought — contain what seem to be snippets of DNA from other species, suggesting they were shaped not only through divergent evolution but also by occasional hybridization. The small warm- and temperate-water clymene dolphin apparently evolved out of a hybrid mix of two other Atlantic dolphins. A bat native to the Lesser Antilles seems to come from three species — one in Central America, one in South America and one that’s extinct. Even most people carry a small quantity of DNA from archaic humans like Neanderthals; in other words, our species, Homo sapiens, has also been influenced by hybridization…