ABSTRACT
This chapter examines the findings pertaining to some of the most basic biological factors. Biological variables are all those having to do with life. In a narrower sense, variables having to do with behavior, emotions, cognition and the like are conceptualized as being outside the realm of biology. Sex ratios are of interest to biologists because these ratios vary considerably from species to species, a fact that continues to beg for evolutionary as well as physiological explanations. In most mammalian species, sex is basically determined genetically, but in some types of animals, environmental factors are largely responsible for whether an individual becomes a male or a female. A series of studies are worth mentioning to further illustrate factors that influence secondary sex ratios. Many factors can have both short-term and long-term effects on secondary sex ratios.
