Marxists argue mode of production (who owns and controls society's productive forces- tools, machinery, materials, land and labour) determines the shape of all social institutions. In modern society, capitalist class have control- as the means of production evolve, the family does too. Marx calls the earliest, classless society as 'primitive communism'- no private property, members owned production communally. At this stage, there was no 'family' as such, instead Engles calls it a 'promiscuous horde' with no restrictions of sexual relationships.