Final answer:
The nuchal crest is a pair of bony lines on the posterior skull. It is more prominent in males than in females and is involved in the physical differences, or sexual dimorphism, observed between the sexes in some species.
Step-by-step explanation:
The term nuchal crest refers to specific bony structures found on the posterior skull. In humans, the superior nuchal line is a paired bony line on the posterior skull that extends laterally from the external occipital protuberance. This structure is more prominent in males than in females, which is likely to be the focus of the question. However, the additional context provided from a study (Gross et al., 2007) about coloration disparities in males and courtship displays seems to be about a non-human species, potentially a type of bird or fish, where males display varying degrees of color to attract females. Such sexual dimorphism is common in the animal kingdom, where the physical differences between males and females of a species are often related to reproductive strategies and courtship behaviours.