The bond between dogs and their humans triggers the same neurochemical cascade that cements a mother's attachment to her newborn—a connection that evolution somehow engineered across species lines.
When a human and a dog gaze into each other’s eyes, both of them release oxytocin — the same hormone released between a human mother and her infant during nursing — and Japanese researchers reported in 2015 that this cross-species chemical feedback loop appears to be unique to dogs and their humans and does not occur in wolves
Brendan Brown