Foreskin
In modern times, there is controversy regarding whether the foreskin is a vital or vestigial structure. During the physical act of sex, the foreskin reduces friction, which can reduce the need for additional sources of lubrication. "Some medical researchers, however, claim circumcised men enjoy sex just fine and that, in view of recent research on HIV transmission, the foreskin causes more trouble than it’s worth." The area of the outer foreskin measures between 7–100 cm2, and the inner foreskin measures between 18 and 68 cm2, which is a wide range. Regarding vestigial structures, Charles Darwin wrote, “An organ, when rendered useless, may well be variable, for its variations cannot be checked by natural selection.” In the March 2017 publication of the Global Health Journal: Science and Practice, Morris and Krieger wrote, "The variability in foreskin size is consistent with the foreskin being a vestigial structure." It has been found that larger foreskins place uncircumcised men at an increased risk for HIV infection most likely due to the larger surface area of inner foreskin and the high concentration of Langerhans cells.