I suggest that you take the broadest possible topic
i.e.one which can encompass almost anything
concerned with gender, sexuality and culture.
Perhaps you could title your dissertation:
'Males and Females ~ a study of the differences '
There are many books on the subject, covering
genetics, physiology, anatomy, upbringing, culture,
environment, intelligence, expectations, etc. etc.
Give yourself a head start by reading the best
account I've ever come across, namely:
HUTT, Corinne : Males and Females
Penguin edition, 1972
ISBN 0 14 08 0563 X