On the internet and in some scientific circles (for example personality type theory of Helen Fischer) there exist various theories regarding masculinity, testosterone and how it relates to jaw size. Human type theory debunks any objective attempt to link jaw size with masculinity and levels of testosterone. Jaw size is genetic trait which is always constant in certain genotype. For example Lincoln type, Voltaire or Plato type man will always have smaller jaw than individual from Bronson type no matter how much testosterone that Lincoln type person can have. Even Bronson type female will always have larger jaw than a man of Lincoln or Plato type.
Let’s take for example popular Plato type actor Denzel Washington:
As you can see his jaw is small, but yet this actor is often titled as “very manly man”.
Now let’s take a look at the jaw of Bronson type actress Lucy Liu.
As you can see the same applies to women when speaking about “femininity”. She clearly has very big jaw yet this woman is not less “feminine” because of it and women with smaller jaws are not more feminine than women with larger jaws or vice versa. Size of jaw is inborn genetic trait and not measure of “femininity” or “masculinity”. It’s true that larger amounts of testosterone will have some effects on bone growth (including facial bones) and thus a person with larger quantities of testosterone can have a little bit thicker facial bones but his overall jaw size will never exceed proportional limits of his genotype.
According to human type theory one correlation is valid regarding jaw size: size of jaw directly is related to the size of occiput where visual cortex is located. You can read more about it in other articles in our website.
On the final note it can be said that “femininity” and “masculinity” are more an expression of psychological behaviour than a biological trait and also the exact definition of what is “feminine” and “masculine” changes overtime together with constant change of accepted societal values.