Here are some interesting pieces of information from Scientist, Walt Brown's book:
Sexual Reproduction
If sexual reproduction in plants, animals, and humans is a result of evolutionary sequences, an unbelievable series of chance events must have occurred at each stage.
a. The amazingly complex, radically different, yet complementary reproductive systems of the male and female must have completely and independently evolved at each stage at about the same time and place. Just a slight incompleteness in only one of the two would make both reproductive systems useless, and the organism would become extinct.
b. The physical, chemical, and emotional systems of the male and female would also need to be compatible.
c. The millions of complex products of a male reproductive system (pollen or sperm) must have an affinity for and a mechanical, chemical, and electrical compatibility with the eggs of the female reproductive system.
d. The many intricate processes occurring at the molecular level inside the fertilized egg would have to work with fantastic precision—processes scientists can describe only in a general sense.
e. The environment of this fertilized egg, from conception through adulthood and until it also reproduced with another sexually capable adult (who also “accidentally” evolved), would have to be tightly controlled.
f. This remarkable string of “accidents” must have been repeated for millions of species.
Either this series of incredible and complementary events happened by random, evolutionary processes, or sexual reproduction was designed by intelligence.
Furthermore, if sexual reproduction evolved, the steps by which an embryo becomes either a male or female should be similar for all animals. Actually, these steps vary among animals.
Evolution theory predicts nature would select asexual rather than sexual reproduction. But if asexual reproduction (splitting an organism into two identical organisms) evolved before sexual reproduction, how did complex sexual diversity arise—or survive?
Finally, to produce the first life form would be one miracle. But for natural processes to produce life that immediately had the capability to reproduce itself would be a miracle on top of a miracle.