... no eitje, arranged marriage may have existed in some cultures, but even in those who you were married to did not always necessarily determine who you were producing children with.
So let's here from someone who has studied human evolution.
Height (and not race) is the major factor in genital-size as far as averages go, but even then it doesn't produce any wild variation. We're talking something like one inch of length and a proportional increase girth per foot of height difference. So, yeah, a guy who is 5'6" should not by any means have something resembling a transplanted thumb between his legs. That dude just got a raw deal.
Ladies, want to try your hands at being a size queen?* Look for guys who are abnormally tall, heavily muscled, narrow-hipped, with what appears to be disproportionately small cranial capacity, and of low intelligence. This still won't be any sort of guarantee, but the odds will be in your favor.
Guys, want to find a girl who's blissfully tight?** Basically look for the exact opposite. You want a girl who's short, unusually intelligent, has a large head and high-brow, curvy hips, and lithe build. Same disclaimer applies as above.
As for dick-evolution, human beings tend to mate for the long term, often for life***, while producing few young. The vast majority of the sex we have is for pleasure, and as such this has effected mate-selection as we became increasingly K-selective (producing fewer young with more investment in their development) as a species. The result: we have the largest dicks and the smallest balls, relative to body mass, of any primate.
*If you have a small penis, my condolences... but seriously, get over it. Fretting about that shit will not improve your attractiveness, now will it make you bigger. If a woman can get herself off with her finger, all is not lost.****
**Childbirth permanently alters the cervix. The. Cervix. Not the vagina. In some rare cases scarring of the vagina during labor will actually result in increased tightness.
***Those who argue based on primate behavior and sex drives that infidelity is a natural and therefore excusable occurrence are wankers. If sexual hedonism were a good thing for our species, we wouldn't form the intense bonds we do with our partners, nor would we feel the intense anguish at the betrayal of those bonds. Using the sort of arguments favored by those who support the acceptance of infidelity, you could also argue that it should be acceptable for men to commit murder, rape, infanticide, and genocide. All are quite normal amongst chimpanzees.
****Unless you have infantile penis syndrome. That just sucks.