A quick Google search finds this page, which cites biological advantages to sequestering hemoglobin within red blood cells. -- Gene On Friday, October 12, 2018, 5:18:45 PM PDT, Dan Asimov <dasimov@earthlink.net> 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 showed 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 ... ... -----