LiveScience: Many reptiles have no sex chromosomes. Instead, their gender is determined by temperature. In crocodiles, for example, males are hot: eggs incubated in sand above a certain “”pivotal temperature”” almost always hatch males. That could spell trouble, because Earth is warming so fast that natural selection may not have time to adjust pivotal temperatures. Female crocodiles may become scarce. Some experts think fish are in the same hot water because temperature-dependent sex …