Expert: Dana Krempels, Ph.D. - 10/12/2007

Question
QUESTION: Hi.

I have read that testosterone levels in males facilitate male facial characteristics, such as chin, jaw, and cheekbones. I'm wonder whether if you took two identical twins and administered testosterone to one and reduced the level of testosterone in the other, would they appear different after puberty?

ANSWER: Dear Marc,

Most physical characters are affected by both Nature (genes) and Nurture (environmental influence), and exposure to testosterone would go under the latter heading.  

It is probable that different testosterone levels in identical male twins could result in somewhat different facial features.  High testosterone levels promote the development of a heavy brow and large, square jaws, within the limits of the genome, so the twin with more testosterone would probably have more masculinized features.

Hard to say, since no one would ever do this test in humans for ethical reasons.  :)

Hope that helps!

Dana

---------- FOLLOW-UP ----------

QUESTION: Thanks for your response.

So if a parent doesn't have a characteristic such as strong jaw or high cheekbones, the child will most likely not obtain it no matter the hormone levels. Correct?

Answer
Dear Marc,

If the genes do not encode formation of a "strong jaw" or high cheekbones, then additional testosterone will not make those appear, though they may slightly change such features--but only within the limits of what's encoded in the genome.  Don Knotts, even on testosterone, would still look like Don Knotts. :)

Artificially added testosterone has so many other health risks that it would not be advisable to try this.

Hope that helps.

Dana