Neurology, not psychology. I'm not just talking about behavioural tests, although there's plenty of evidence there as well. I'm talking about brain dissections comparing the actual brain development between many species at different ages. Sexually mature, "adult" cats and dogs don't develop the brain structures present in adults of their wild associates. After several generations of ferality, however, these structures show up again.
If you spoon-feed your child from birth until maturity, and in other ways inhibit their ability to use their hands, they will fail to develop the motor skills to feed themselves. This will show up as underdeveloped brain tissue in the region of the brain responsible for fine motor skills. The potential is still there in their DNA, but without practice and necessity, those structures just don't develop. If you were to then turn this child out on their own, they wouldn't be able to learn how to hold a spoon because they would have missed the developmental window. Oh, they might be able to fist grab it and manage to shove some food in their mouths, but they would never do calligraphy.
It's the same thing with kibble-feeding your cats for 2 years and then throwing them out in the backyard to fend for themselves. Their brains just don't know how to do it. Oh sure, they still have enough instinct to chase and pounce on mice, and they might be able to "survive." But they certainly wouldn't thrive and as soon as the food supply gets tight, they'll be the first to go.
Saying that being held responsible is the difference between animals and humans is completely arbitrary. He wasn't saying that people aren't animals. He was saying that animals are people.
You speak in riddles. I've had a bank account since I was 6.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker