Domestic dogs inherited complex behaviors, such as bite inhibition, from their wolf ancestors, which would have been pack hunters with complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations, and these attributes have given dogs a relationship with humans that has enabled them to become one of the most successful species on the planet today.:pages95-136
The domestic dog (Canis lupus familiaris when considered a subspecies of the wolf or Canis familiaris when considered a distinct species) is a member of the genus Canis (canines), which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore. The dog and the extant gray wolf are sister taxa as modern wolves are not closely related to the wolves that were first domesticated, which implies that the direct ancestor of the dog is extinct. The dog was the first species to be domesticated and has been selectively bred over millennia for various behaviors, sensory capabilities, and physical attributes.
^ Bridgett M. von Holdt, Emily Shuldiner, Ilana Janowitz Koch, Rebecca Y. Kartzinel, Andrew Hogan, Lauren Brubaker, Shelby Wanser4, Daniel Stahler, Clive D.L. Wynne, Elaine A. Ostrander, Janet S. Sinsheimer and Monique A.R. Udell (19 July 2017). "Structural variants in genes associated with human Williams-Beuren syndrome underlie stereotypical hypersociability in domestic dogs". Science Advances. 3 (7): e1700398. Bibcode:2017SciA....3E0398V. doi:10.1126/sciadv.1700398. PMC 5517105. PMID 28776031.
Yes, though it is usually better to use dog clippers if you can get them. Dog clippers are designed to cut dog's hair, which usually has a coarser top coat and a softer undercoat, but not every dog has this type of coat. For instance, Yorkies and similar breeds only have one type of hair, more like humans, and so it actually makes perfect sense to use human clippers on this kind of dog.
The scientific evidence is mixed as to whether companionship of a dog can enhance human physical health and psychological wellbeing. Studies suggesting that there are benefits to physical health and psychological wellbeing have been criticised for being poorly controlled, and finding that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.