Cross-species studies of animal populations have shown that cubs who are isolated from their mothers within a month of birth often show strong aggression  For example, when looking for food, he is aggressive and fighting for food, while other cubs give in and he is still fighting for food
Babies who are adopted in the first three months of life often behave aggressively in childhood.
 The hypothesis that explains this phenomenon is that the aggressive problem is due to the lack of social training guided by parents at the newborn stage