Sperm undertake a journey into the mother's body until they reach the ovum. Only a thousand out of 250 million sperm succeed in reaching the ovum. At the end of this five minute race, the ovum, half the size of a grain of salt, will let only one of the sperms in. That is, the substance of man is not the whole semen, but only a small part of it. This is explained in the Surat al Qiyama as follows:

Does man reckon he will be left uncontrolled [without purpose]? Was he not once a drop of ejected semen? (Quran, 75:36 37)

As we have seen, the Quran informs us that man is made not from the entire semen, but only a small part of it. That the particular emphasis in this verse announces a fact only discovered by modern science is evidence that the Quran is the word of Allah.