The right amydala is a "primitive" structure in our brains which reacts strongly and immediately to the sight of animals. Our amygdala would strongly have influenced our behaviour tens of thousands of years ago or more, when we lived in small groups on the savanna. We had to react immediately to animals which posed dangers to us, such as lions and snakes, and we also had to react strongly to animals that we might kill and eat. Apparently, however, our amydala also possessed the ability to react positively to animals. If we hadn't had that instinctive ability, how would we have been able to domesticate so many animals?
Florian Mormann, Julien Dubois, Simon Kornblith, Milica Milosavljevic, Moran Cerf, Matias Ison, Naotsugu Tsuchiya, Alexander Kraskov, Rodrigo Quian Quiroga, Ralph Adolphs, Itzhak Fried & Christof Koch have carried out a study on human response to animals and located the origin to our instinctive reactions to our amygdalae - or rather, to one of them!. The title of their paper is "A category-specific response to animals in the right human amygdala". Yes, because fascinatingly, it is only our right amygdala that reacts to animals!
Read the press release here. It's really interesting!