Amoeba don't have an "urge" to reproduce. They just do. Sexual drive is an evolutionary development of higher cortical processes to make sure the organism takes care of that critical function when there are so many other choices to make (like hunting, cavorting, etc).
"Better adaptability" is the sine qua non of evolution. If an organism develops a mutation that gives it an advantage over another, it will flourish at the other's expense. Similarly, if the mutation disadvantages the organism (such as cancer), it will die out.