It is quite possible--overwhelmingly probable, one might guess--that we will always learn more about human life and personality from novels than from scientific psychology
Colorless green ideas sleep furiously.
It's roughly the case that if systems become too complex to study in sufficient depth, physics hands them over to chemistry, then to biology, then experimental psychology, and finally on to history. Roughly. These are tendencies, and they tend to distinguish roughly between hard and soft sciences.
Peter Kropotkin was surely on the left. He was one of the founders of what is now called 'sociobiology' or 'evolutionary psychology' with his book Mutual Aid, arguing that human nature had evolved in ways conducive to the communitarian anarchism that he espoused.