Yaniv asks: “If G-d created everything for a specific reason, why do men have nipples? And did the first man have a navel? Thanks for your answer!”
Greetings Yaniv, and thank you for your question.It is true that everything was created for a purpose, and with immense wisdom. This wisdom is reflected in the fact that G-d created everything as intricately planned and compact as possible. It doesn’t make sense that a woman would have two wombs in her stomach, one for male fetuses and one for female fetuses, and therefore at the beginning of the fetus’s development, there are elements in the process that apply to both male and female. For this reason, until the sixth week, the fetus in the womb is bisexual: it can develop into both female and male, because it has all the components to develop into either of the two sexes. The gender of the fetus will be determined later by the chromosomes that shape it from the sixth week onwards.
This compact mechanism is reflected in part in the creation of nipples in the young embryo, which for male fetuses stops developing, but in the female fetus continues to develop. The reproductive organ of the male also undergoes a similar process in the fetus and continues to grow.We can see this design in all mammals, not just humans. Even male mice and dogs have nipples. This is simply the best way in which the fetus can develop into both a male and a female. For the exact same reason, human beings have a navel (called by children a “belly button”), even though there is no use for it after the baby leaves the womb and is no longer attached to the umbilical cord. A male’s nipples, like the navel, are a relic from when he was fetus.
Now to your question of whether the first man had a navel / nipples? On the one hand, you could say the first man was missing them, because he was not born as an embryo (and nipples and a navel are relics from when we were fetuses inside our mother). Adam's sons were of course just like us, because they were born in a normal way from a father and mother, and they developed as fetuses.
However, it is possible that G-d created the first man with a body and appearance that would be given to all persons born after him, in which case he would have been born with a navel. This explanation fits what we have been taught by our sages: “Rabbi Yochanan said: Adam and Eve were created twenty years old.” (Genesis Rabbah 14). We see that man was created as a 20 year old adult and knew immediately how to speak, without having to grow up as a child and teenager. In the same way, it would be logical to assume that Adam was born as if he had passed all phases of human development including as a fetus. This is undoubtedly an interesting idea.