Abstract thinking is not only for humans.
Some apes do it too, as so do many octupai.
My dog will take his food and push it into a rat hold to fed the rats so he can feed their babies and provide him with a relief from boredom when they grow up and provide him with the sport of chasing the little critters.
My pigeons are smart as can be, too. When I only fed the males in the morning they will eat extra to regurgitate some of the food to their mates so they won't starve to death. I consider that . That's abstract.
http://www.pbs.org/wgbh/nova/nature/tool...
The only biological characteristic I can say definitely distinguishes humans from other animals is our opposable thumb. Thank G-d other wise the pigs and ;monkeys would lock us up in cages and be observing us, claiming THEY are the highest form of life on this planet.
And we also are the only creature who bothers to try to leave this planet and go up to the stars.
It is very likely we do this because a virus has altered our behavior patterns some time in the past and is using us as a vehicle to get back to where they came from.
Viruses alter the behavior of many creatures, from ants to humans.
People infected with a cat virus begin to steal and become promiscuous as the virus can be spread sexually and through cat dung. If they steal they will have more time to spend raising cats and buying cat food and having sex with lots of people to spread that virus.
Most of us humans think we aren't animals but we eat, defecate, reproduce and die just like other animals so if it walks and talks like a duck it must be a duck too.