Is Gender a Biological Construct?

Discuss whether gender is a biological construct.

Proponents of a school of thought called natural differentiation using the theory of natural difference have argued that aspects of human biology ranging from hormones to chromosomes to brain size to genetics are responsible for innate dissimilarities in behavior between females and males. And since these traits are observable across all cultures implies that natural factors are responsible for the inequalities between genders. From this perspective, gender is biological. With this background, argue for or against the notion that gender is a biological construct.