In some cases, a child is born with a mix between female and male genitalia. The evolutionary dynamics of sex determination. Laqueur suggests that from the Renaissance to the 18th century, there was a prevailing inclination among doctors towards the existence of only one biological sex the one-sex theory , that women and men had the same fundamental reproductive structure. A primary reason was that we were interested in reviewing whether and how articles referenced sex and gender in studies on genetics and health, a goal that required the inclusion of articles that did not emphasize sex or gender. Just remember that biological or assigned sex is about biology, anatomy, and chromosomes. However, behavioral differences between individuals can be statistically partitioned, as studied by behavioral genetics. They demonstrate that double-strand DNA breaks DSB are important for segregation of the hemizygous X and present evidence that DSBs could mediate sister chromatid synapsis pseudosynapsis , instead of the typical synapses formed between homologs. The third section describes persistent and unexplained gender differences in health, and reviews biological and social explanations. They go further and show that different genes function to provide feedback on autosomal synapsis and DSB repair pathways. In addition to these 3 leading public health journals, we reviewed research articles published in Nature Genetics. These individuals might refer to themselves as transgender, non-binary, or gender-nonconforming. Although sex is included frequently as a control or stratifying variable, few articles articulate a conceptual frame or methodological justification for conducting research in this way, and most are not motivated by sex or gender differences in health. A Comprehensive Grammar of the English Language, for instance, refers to the semantically based "covert" gender e. Within the wider culture, families too have their norms. The degree of decision-making and financial responsibility expected of each gender and the time that women or men are expected to spend on homemaking and rearing children varies between cultures. How does the interplay of gender-specific variation in environments and sex-specific variation in biology yield differences from birth to death in health trajectories and outcomes for men and women? It varies from society to society and can be changed.