Scientists are still unsure what caused the massive extinction that killed off the dinosaurs. They know that at least one major impact with a comet or asteroid helped things along, but dinosaurs still survived for thousands (millions?) of years afterward. There are additional hypothesis on what other things may have contributed to the final downfall, but I wonder if an imbalance in gender had something to do with it.
We know that slight variations in temperature can effect whether certain species of fish and reptiles are born male or female. Global Warming is causing fish in South America to be born predominantly male.
A small increase in water temperature among sensitive fish like the South American pejerrey can result in a population that is 98% male.
…in some finned species, like the Atlantic silverside — as well as in many reptiles — sex is determined not by genetics but by temperature: the undifferentiated embryo develops testes or ovaries on the basis of whichever option conveys evolutionary advantages for that particular environment. Now, in a study published in the July 30 edition of the scientific journal Public Library of Science, Natalia Ospina-Alvarez and Francesc Piferrer have gone a little further in explaining how that mechanism works. In laboratory tests, they have demonstrated that higher water temperatures result in more male fish.
If you have an imbalance in the number of males or females born, or surviving to reproductive age, you can have an evolutionary pressure to either correct the imbalance, or a slow (or not so slow) push toward extinction. If some post impact or even pre-impact environmental pressure was causing an imbalance in male/female survival, you could get a slow decline in population, especially if it is a disproportionate number of males to females.
I would guess this has been considered and investigated by the scientific community, but I haven’t had time to research it yet. The fish article just got me thinking.