answer:Both animals and human children go through stages of development. And it’s during these stages that learning takes place. This is when the synapses of the brain are firing and making webs of connection. If the young ones are denied those experiences, both physical and emotional, during the optimum time for learning, they are impaired for life because those brain connections weren’t formed in the early stages. Because of the brains incredible adaptability (called neuro-plasticity) and learning capabilities, some degree of the missing info can still be learned in adulthood. And it varies from one person to another. But they will never achieve the same degree of neural connections because the optimum window for that has closed. If babies are not held, cuddled and interacted with, they will have lifelong difficulties forming connections. This was markedly demonstrated years ago after the wall came down and many of the babies from overcrowded orphanages in countries part of the former USSR were available for adoption to Americans. But many many of these kids had severe deep seated emotional problems falling under the general term “attachment disorder”. While they may not have been physically abused or hit or anything like that, the orphanages were horribly understaffed. Basically these babies were pretty much confined to their cribs 24/7 (even past the age where most babies are crawling, learning to walk etc.) with almost no interaction with caregivers other than feeding, diaper changes etc. No cuddling, being held when they cried, nothing. Even tho their new adoptive parents were very loving, thrilled to have them, doting on them, giving them all the loving attention they had missed, for many it was just too late. Their view of the world and people in it was still a cold and sterile place to them, bereft of tenderness and care. They had literally never learned how to connect emotionally to caregivers and parents because no one had the time to connect with them. Their emotinal “map” had huge holes in it. Large chunks of missing information were never experienced or learned. The critical optimal time for that had passed. These neural pathways for loving and responding to love and connection had not been formed so they were going thru life with a very faulty map filled with all kinds of gaps. And the examples you gave of the deprived kittens is quite similar except that there missing info was physical rather than emotional. The neural pathways had not formed at the crucial age and it was so much more difficult for them to navigate this totally different world.