130 Male Gender Bias and Levels of Male Hormones During Fetal Development
Male and Female Estrogen and Testosterone
Hormone Regulations
It is pertinent to mention here that females can convert testosterone into estro-
gen by the aromatase enzyme (CYP19A1 gene), however a male cannot convert
estrogen into testosterone. Therefore, a high level of testosterone in females
may not have any adverse effects. The expression levels of aromatase enzyme
may be one of the reasons for the gender bias.
The aim of hormones is to execute specific tasks precisely at specific times
and with specific outcomes. Therefore, detrimental outcomes for offspring can
result from exposure of a mother to any endocrine disruptive chemical(s)
(EDCs) that can subsequently reach a fetus [33,34,44–60,63–66]. As shown in
Figure 5.2, testosterone plays a central role in the development of the male
brain, especially during weeks 8–24 of gestation. In female fetuses there
appears to be no estrogen exposure during gestation. Estrogen exposure occurs
later, after the postnatal period, when estrogen is required to lead a female
towards puberty. As we have detailed in Chapter 4, fetal testosterone has a
precise role in male brain development and any synthetic or natural chemical
that can increase the levels of testosterone or bind to androgen receptors can
modify the normal brain development (both male and female), as proposed in
EMB theory [3–6]. Here we describe some of the endocrine disturbing
chemicals that can have a potential detrimental effect on fetal development
[33,34,44–60,63–66].Are there Synthetic Chemicals that Humans Are Not
Evolutionarily Exposed To?
Over the last four decades, a substantial increase in the prevalence of autism
has been reported, from 4 to 5 children per 100,000 in the 1960s to around
one in 45 children in 2015 [1,2]. We maintain that exposure of the human824Hormone secretion1BirthAge (years)2 10 20 30 40Female
(estrogen)Male
(testosterone)Figure 5.2 Normal ranges of male and female sex hormones over the human lifespan.