Muslim scholars consider a fetus that has passed its fourth lunar month after conception to be a living human being.

Scientifically speaking, life is a series of molecular events and biochemical reactions in each cell of the human body, events, and reactions that should not be confused with ruh (the human soul) of which we have very little knowledge.

Life begins in the embryo at the time of conception. This is despite the fact that life was present even in the precursors of the ovum and the sperm that were lying dormant in the testes and the ovaries. In fact, both the male sperm and the female ovum have life in them, even before fertilization takes place, but they have no soul. 

The Qur'an says what means the following: 

[There was a time when man was non-existent and he was not even mentioned.] (Al-Insan 76:1) 

It is difficult to imagine that as recent as 150 years ago, we did not know that just a single spermatozoon out of 400 million present in the father's seminal discharge at any one time fertilized a single ovum (egg) of the mother, causing someone to be born, and that 3,999,999 sperms died in this process. Nowadays, because we know about this struggle for survival, we can very well imagine how lucky and important each of us is to have survived and be alive today. 

It is the single cell of the male (spermatozoon) containing an X or Y chromosome that determines the sex of the offspring, for the ovum contains only an X chromosome. The child becomes a female if the combination contains XX chromosomes or becomes male if the combination contains XY chromosomes.

The Qur'an says what means the following:

[O mankind! Be careful of your duty to your Lord Who created you from a single soul and from it created its mate and from them twain hath spread abroad a multitude of men and women. Be careful of your duty toward God in Whom ye claim (your rights) of one another, and toward the wombs (that bare you). Lo! God hath been a watcher over you.] (An-Nisaa' 4:1) 

[It is He Who created you from a single person, and made his mate of like nature, in order that he might dwell with her (in love). When they are united, she bears a light burden and carries it about (unnoticed). When she grows heavy, they both pray to God their Lord, (saying): "If You give us a goodly child, we vow we shall (ever) be grateful."] (Al-A`raf 7:189)

Receiving the Soul (Ruh)

Muslim scholars believe that human life begins soon after the fourth lunar month of conception when the fetus becomes viable, that is, fit to live. Of particular significance are certain associated events the Prophet Muhammad (peace and blessings be upon him) related:

The creation of each one of you is brought in the womb of his mother for forty days as a germ cell. Then for a similar period, he is an embryonic lump (hanging like a leech, known as `alaqah in Arabic). For another forty days, he is a mudghah (like a chewed-up substance: shape of a four-week-old embryo); then an angel is sent and he (the angel) blows in him the ruh (soul). After this, the angel is ordered to write down four words. He is told to write down the child's [future] livelihood, his life duration, and whether he is to be miserable or happy. (Al-Bukhari ) 

One of the Prophet's Companions and a renowned Muslim scholar, Ibn `Abbas, stated that the breathing-in process takes place within 10 days after the four—month period. If the fetus were to die before this process, there should be no Janazah Prayer (funeral prayers). It is to be noted that it is the foreordainment and the breathing that generate the quality of a human being.

Animals have no such ruh. This "breath" may be similar to the breath by God when He first fashioned Adam. Of course, the idea of God's breath is metaphoric, indicating love and ownership, not physical breath.

Muslims accept that the nature of the soul is what God relates in the Qur'an in words that mean the following: 

[Then He fashioned him and breathed into him from His ruh; and He gave you (the faculties) of hearing, sight, and feeling. Little thanks you give.] (As-Sajdah 32:9) 

[When I have fashioned him and breathed into him from My ruh] (Al-Hijr 15:29)

If God had not breathed into the mold of clay from His own ruh, we human beings would have been statues of clay without any life and without soul. In this breath that comes from God and which we call ruh is embodied whatever potential good and positive qualities human beings possess. These must have been present in this ruh, which probably entered the fetus in the womb when the fetus became viable soon after four lunar months of conception.

Life and Blood

Some people say that life is in the blood, so we receive blood in the womb and we cease to live when we die and our blood comes to rest.

Physically, blood acts only as a nutrient. It can be drained out completely from the whole body, and be replaced, and the person still will be living and will have a soul. The heart can be removed from the body (as we used to do with the frog's heart and put it in saline solution) and it will keep on pumping for a few days. The heart will have life for a few days, but where is the soul? 

The important question here is this: Where does this soul reside in the body? If one's limb is amputated, this amputated limb does not have a soul, although it still has life and the limb can be reattached. So again, where is the soul? All four limbs can be amputated and still the soul is intact in the remaining body. 

Then does the soul reside physically in the blood? No, because the blood can be drained out completely and replaced. Does the soul live in the germinal layer of our reproductive organs, that is, the testes and the ovaries? No, because the soul is still present in the absence of our reproductive organs. Although we know that the soul is present somehow in the living body, we do not know where it is located. 

Moreover, it may be fruitless or futile to seek out any special locus or resident place for a spiritual entity, of which God has given us very little knowledge. The Qur'an clearly states that the ruh is a divine matter whose secret is known only by God.

[And they ask you about the soul. Say: The soul is one of the commands of my Lord, and you are not given aught of knowledge but a little.] (Al-Israa' 17:85)