Are square jaws a masculine trait?

Recently I was asked my opinion on square jaws by a reader of this blog. I really didn't know where to start though. I thought I knew what the reader was getting at, but didn't think there was a good enough definition for the term, really. Sometimes "square" seems to refer to a square shaped face and at other times a defined jaw line.

What "square" means in the fields of medicine and anthropology...

But John Hawks, a paleoanthropologist and professor of anthropology, has a web site that gets to the point nicely. The angle of a person's jaw, shown below, differs somewhat between men and women. "In males, the angle [sic] is closer to 90 degrees. In females, this angle is greater, up to 110 -120 degrees." Hence the term "square jawed", I would assume.

mandibular or gonial angle

Other articles say this isn't a reliable determinant of gender though. Ethnicity and other factors play a role in determining the gonial angle. But since these articles are written by forensic anthropologists, their interest lies in being able to determine sex from skeletal remains. Our interests are different. We are looking at people face to face so have visual clues regarding age and ethnicity.

Jaw angle does affect face shape...

Another thing I learned from reading books on anthropology and forensic facial reconstruction is that the gonial angle definitely does affect that shape of one's face from the front. The squarer the jaw, the more likely the person will have a round or square face, as opposed to an oval or triangle-shaped face.

Androgens affect face shape...

We know this. We can SEE this. But here are some articles that show the difference prenatal testosterone makes. When a person's ring finger is longer than his or her index finger, this results in a lower 2D:4D ratio (2nd digit to 4th digit ratio) which signifies higher androgen exposure in the womb.

'Manly' Fingers Make For Strong Jawline in Young Boys (Note that this 2012 study had a very small sample size of 17. See the abstract here.)

Less prenatal androgens resulted in a more feminine, triangular, face shape, as seen on the left. This differs greatly from the masculine face, which is square-shaped.

Second to fourth digit ratio and face shape (2005 study of 106 volunteers)

Again, the more prenatal exposure to androgens, as seen on the far left, the squarer the face shape.

To be continued...