Like sociobiology, it is a purely post-hoc descriptive model. Neither has produced new information.
But if a bozo like the malignant Singer can't tell junk science when he sees it, and wants to try adapting it to junk political philosophy like Marxism, I think that's just fine.
It means he will spend his time in a futile and ultimately dead-end pursuit, rather than other, more harmful and pernicious of his degenerate activities.
Copernicus's model of a heliocentric solar system was also a purely post-hoc descriptive model. After all, astronomers were quite capable of predicting the positions of the planets before Copernicus.