Expert: Dana Krempels, Ph.D. - 6/1/2008

Question
My question is, what is the reason for the arm length being roughly the same as
a persons height, or the forearm being the same length as a foot? Thank you in
advance

Answer
Dear Georgie,

The simplest answer is that the proportions of the human body are adaptive.  Any trait exhibited by any animal can be:

adaptive - increase the chance for reproductive success

maladaptive - decrease the chance for reproductive success

neutral - not affect the chance for reproductive success

Humans with certain arm and leg ratios in our ancestral past may have been better at running or climbing or any other activity that would increase its ability to collect food or capture prey, and the most successful body forms would be the ones that allowed their owners to best exploit environmental resources.  This, in turn, would foster greater reproductive output (all other traits being equal), and humans would be naturally selected for particular proportions.

The short answer is that the proportions we have are the ones that work the best for our mode of locomotion.  Which we do a lot less of, now that we sit at our computers all day.  ;)

Hope that helps.

Dana