“Compared to other animals, humans are born prematurely, when many of their vital systems are still under-developed,” writes Yuval Noah Harari in his widely-celebrated book SAPIENS: A Brief History of Humankind. “A colt can trot shortly after birth; a kitten leaves its mother to forage on its own when it is just a few weeks old. Human babies are helpless, dependent for many years on their elders for sustenance, protection and education.”
This could at first glance be taken as a disadvantage, but actually it seems to have forced us to evolve in different ways.
“This fact has contributed greatly both to humankind's extraordinary abilities and to its unique social problems. Lone mothers could hardly forage enough food for their offspring and themselves with needy children in tow. Raising children required constant help from other family members and neighbors. It takes a tribe to raise a human. Evolution thus favored those capable of forming strong social ties.”
Therefore, one can consider the “nuclear family” to be a kind of human devolution.