12 Introduction to Autism Spectrum Disorders
provided the first specifically demonstrated evidence that individuals with
autism have higher fetal male hormonal activity than typically developing
individuals. This research suggests a correlation that involves elevated levels
of fetal testosterone [57]. However, it does not really explain the causation
behind the surge of autism over the past few decades. More recent analyses of
EMB hypothesis have not found persuasive digital ratio evidence. Therefore,
Guyatt et al. [62] analyzed a large number (6,015) of children with ASD and a
corresponding control group but were unable to find a 2D:4D association
related to ASD for either males or females. Here, it must be emphasized that
ASD is a spectrum and a clear‐cut answer to a spectrum that relates to fetal
brain development may not be possible. We will further explain this conun
drum in Chapter 5.Connecting the Dots
As illustrated in Figure 1.7, over the past four decades, a startling rise in
ASD prevalence has been reported, rising from ~1 per 10,000 in the 1960s,
to about one in 45 children today. We maintain that the alarming 20‐fold
increase in autism in recent years is due to exposure of the human popula
tion to an increasingly diverse set of synthetic chemicals including fra
grances, many of which involve endocrine disrupting chemicals (EDCs)
(male and female hormone‐like chemicals) [63]. Published laboratory and(^42)
High ration
0.98 1.00
Figure 1.6 Possible connection between 2D:4D ratio and autism and differences between
male and female 2D:4D ratio, associated with fetal testosterone (see Chapter 5 for more
detail). Source: Adapted from https://stynoski.wordpress.com/research/digit‐ratios/.