I have read that the Y-chromosome is more "brittle" (for lack of a better word) than the others in the human genome. Therefore, as environmental factors get wo

I have read that the Y-chromosome is more "brittle" (for lack of a better word) than the others in the human genome. Therefore, as environmental factors get worse, the likelihood of females increases. Rich, not too old males are in pretty good shape, so their progeny should be split between gender. Less-rich, or old, or disadvantaged folks should be in worse shape leading to increased XX's. It's inductive reasoning, but most of the folks I've know the last 10-20 years have had daughters - older parents, often in chemical laboratories.