Perhaps this is what you recall? "Also, the biconcave shape allows RBC's to undergo extreme deformations while maintaining a constant surface area for gas exchange." Canham, P.B. "The minimum energy of bending as a possible explanation of the biconcave shape of the human red blood cell. J. Theoretical Biology, 1970. At 05:17 PM 10/12/2018, Dan Asimov wrote:

On this topic, I remember c. 8th grade being shown a film addressing this topic, that concluded the lenticular shape of the red blood cell — i.e., its hourglass cross==section — was exactly what some computer simulation shoowed was ideal (for exactly what conditions, I don't recall).

I later learned that the film was funded by a possibly biased organization, and even so I don't know if those claims stand the test of time (c. 58 years since 8th grade).

—Dan ----- ... why we had red blood cells ... ... -----