Answer:
Because either humans are passing away quickly or there are a lot of child births (Maybe even both)
Explanation:
3:1 the dominant allele would show up in 3 and there would be recessive in 1
I think you wrote this wrong? Is it not round rr vs wrinkled RR?? I'll answer it with that assumption:
You are crossing a rr with an RR:
You only get Rr back so they will phenotypically be all wrinkled
If you are crossing rr with an Rr (so a heterozygote wrinkled):
50% will be Rr (wrinkled)
50% will be rr (round)
See my picture for the Punnett Squares for both answers!