I don't know about _most_ important, but genetics is definitely a large factor. Quoting from Heritability of Lifetime Income[1] > we find that 24% (54%) of th

I don't know about _most_ important, but genetics is definitely a large factor. Quoting from Heritability of Lifetime Income[1] > we find that 24% (54%) of the variance of women’s (men’s) lifetime income is due to genetic factors and that the contribution of the shared environment is negligible The Promises and Pitfalls of Genoeconomics[2] sees similar results, coming up with 46% and 58% heritability in women and men, respectively. There's plenty of research here. "Heritability of income" is a good search term. [1] https://helda.helsinki.fi/bitstream/handle/10138/38881/HECER_DP364.pdf https://helda.helsinki.fi/bitstream/handle/10138/38881/HECER... [2] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3592970/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3592970/