Scientists aren't exactly sure why the species of human being we call "Neandertals" died out some 35,000 years ago. For about 10,000 years before that, they coexisted with what anthropologists call "modern humans," or the species of humanity that is genetically indistinguishable from the people walking around today. But modern humans thrived and Neandertals died out, with no clear explanation as to why.
Anthropologists have thought that more sophisticated tool use and what they call "greater social cohesion" helped our ancestors to spread, population-wise, and eventually replace the Neandertals. In other words, "does not work and play well with others" can sometimes damage a lot more than your first-grade report card.
Some newer studies are putting together a picture that includes another factor: Fido. Now of course, anyone who's ever watched Lassie knows that having a dog who can tell tribal elders that one of the young has fallen into a well is a survival trait and will be selected for during the evolutionary process. The genes of species members who do not have such a dog will, unfortunately, die out in that well. A close study of Rin Tin Tin supports this belief, although evidence from Scooby-Doo would suggest that association with some dogs actually puts human beings -- specifically "meddling kids" -- at risk during their prime breeding years and thus endangers species survival.
But real science has looked at archaeological and anthropological evidence and found that sites with lots of fossils of our ancestors also tended to have more canine fossils around. Although the prevailing idea was that humans domesticated dogs sometime around 17,000 years ago, scientists analyzed the different fossil sites and now think that figure may be too late. The earliest finds offer a strong possibility that the human-canine partnership may have begun during the overlap period with Neandertals.
True dogs, as distinguished from wolves, may show up later in human history, but the earlier fossils show a number of doggish characteristics and have been called "incipient dogs." I would lose my Dave Barry fan club card if I did not point out that "Incipient Dogs" would make a good name for a rock band, or in singular, a good name for a Pink Floyd album.
The article at the American Scientist suggests that human beings were able to connect with dogs for many reasons, one of which was that modern humans have a white sclera around the iris of the eye and that helps improve nonverbal communication. Dogs can tell what people are looking at and can tell when people are looking at them. Smaller lid fissures and darker sclera in many primates today may suggest that Neandertals and other human species might have lacked this important communicating tool. It also underscores the tactical failure the British made at Bunker Hill by not using orangutans.
So to sum up, it could be very likely that we human beings exist today in the forms we have because dogs helped us overcome our competition. There is as yet no evidence that Neandertals tried to rely on cats for the same help but died out because the cats were taking a nap.