How does the environment sometimes influence sex determination in certain organisms, contrasting with the chromosomal mechanism in humans?

While humans and many other organisms use a chromosomal mechanism for sex determination, some species exhibit environmental sex determination. In these cases, external factors like temperature, pH, or social cues during development can influence whether an individual develops as male or female. 

For example, in many reptiles like crocodiles and turtles, the temperature at which eggs are incubated determines the sex of the hatchlings. Higher temperatures might lead to one sex, while lower temperatures lead to the other. 

This contrasts with humans where sex is fixed at fertilization by the combination of X and Y chromosomes, regardless of environmental conditions during gestation.