Origin of the domestic dog as the Tibetan people. A population genetic analysis then showed a significant convergence between humans and dogs in Tibet. Like the Tibetan people, Tibetan mastiffs appear to have derived these benefits partially from the EPAS1 gene, acquired through introgression. In 2015, a study found that when dogs and their owners interact, extended eye contact (mutual gaze) increases oxytocin levels in both the dog and its owner. As oxytocin is known for its role in maternal bonding, it is considered likely that this effect has supported the coevolution of human-dog bonding. One observer has stated, "The dog could have arisen only
Invasive species used to describe a non-native or introduced species that has become widespread (p. 136). However, not every introduced species has adverse effects on the environment. A nonadverse example is the common goldfish ("Carassius auratus"), which is found throughout the United States, but rarely achieves high densities (p. 136). Notable examples of invasive species include European rabbits, grey squirrels, domestic cats, carp and ferrets. Dispersal and subsequent proliferation of species is not solely an anthropogenic phenomenon. There are many mechanisms by which species from all Kingdoms have been able to travel across continents in short periods of time such as via