You might look up a brochure called "doh-transgender-experiences.pdf" .
It states that being trans has biological connections, to do with development before birth which influences the sense of self. Inside of the brochure is a link to further references (findings and studies). One explanation are certain hormone levels at certain times before birth, for whatever reason.
In sum, gender identity, whether consistent or inconsistent with other sex
characteristics, may be understood to be "much less a matter of choice and much
more a matter of biology" (Coolidge et al., 2000). The scientific evidence supports
the paradigm that transsexualism is strongly associated with the neurodevelopment of
the brain (Zhou et al., 1995; Kruijver et al., 2000). It is clear that the condition cannot
necessarily be overcome by "consistent psychological socialisation as male or female
from very early childhood" ...
It is understood that during the fetal period the brain
is potentially subject to the organising properties of sex hormones (Kruijver et al.,
2000; 2001; 2002; 2003). In the case of transsexualism, these effects appear to be
atypical, resulting in sex-reversal in the structure of the BSTc, and possibly other, as
yet unidentified, loci (Kruijver, 2004). The etiological pathways leading to this
inconsistent development almost certainly vary from individual to individual, so no
single route is likely to be identified. Different genetic, hormonal and environmental
factors, acting separately or in combination with each other, are likely to be involved
in influencing the development of the psychological identification as male or female.
Psychosocial factors and cultural mores are likely to impact on outcomes (Connolly,
2003).
It may or may not be hereditary.
Transgender people have often been throughout times teachers, advisors and healers.
(as a maybe funny aside many transgender people report being asked by their friends for relationship advice

)
Imo many can access both male and female thinking patterns without having to fit in one box.