We are creatures made up of spirit and matter, body and soul. Our spirit is the immaterial soul, which our senses cannot feel. But our faith tells us it is there. So by way of our soul, we have some share in the nature of the angels.
We can see that we have a spiritual soul in this way. Each of us has a concept or idea of dog in general. Our mental dog is not high or low, long or short, sharp-nosed or pug-nosed. If we hired the very best artist, offered him any sum and his choice of mediums: oil paints, carving, casting etc. , to make an image of our dog, we would get nothing. For no material can hold this concept. So that in us which holds it is not material, but spiritual. This is all the more obvious in our concepts of goodness, truth, justice etc.
Our soul can exist apart from the body. It will never die, because being spiritual, it has no parts, and so cannot come apart. It will live forever in happiness beyond what we can imagine, or in the reverse, eternal damnation. The Book of Wisdom 3:1-4 says: "The souls of the just are in the hand of God, and no torment will touch them. They seemed to die, to the eyes of foolish people, and their departure was considered evil . . . but they are in peace. Their hope is full of immortality."
Each human soul is directly created by God Himself, it is not produced by or derived from the parents. The parents produce only the human body, and do even that, only with the help of God's power. The uniting of the soul with the body is called infusion. Modern biology knows that at the moment of conception, when the 23 chromosomes from each parent join, the complete genetic pattern of a unique being is already present. So abortion is gravely sinful.
Many today think that the human body evolved from lower beings. If they say that this happened without any help from God, it is atheistic evolution. Not only theology rejects that foolish idea, even mere reason rejects it: it supposes that matter could lift itself up and up higher by its shoelaces, as it were, with no outside source for the higher leves of complexity.
Pope Pius XII in Humani generis in 1950 told us we may consider as a possible--not as something proved--that God established some natural laws that would bring about this evolution from lower to higher. Even so, the whole process would depend on God's creative power. This is true especially of the human soul, which, being spiritual, cannot have evolved. We would call this theistic evolution, that is evolution involving the power of God at so many points.
The scientific evidence for bodily evolution is almost non-existent. "Research News" in Science, November 21, 1980, reported that the majority of 160 scientists at a conference at the Field Museum in Chicago said Darwin was wrong in supposing there had been many intermediate forms between species, e.g., between fish and birds. The fossils do not give one clear case of that. So the scientists decided on, "Punctuated equilibria", the theory that a species might stay the same for millions of years, and then suddenly by a fluke leap up into something higher. No solid proof was reported as offered at the meeting.
Pius XII also noted that Catholics must believe, as a consequence of the doctrine of original sin, that all men have descended from the same two first parents. Science News, August 13, 1983, reported that Allan Wilson, of the University of California, Berkeley, said his study of specimens of mitochrondrial DNA from all over the world, showed all existing humans come from one mother, who lived 350,000 years ago. More recent studies by many scientists agree that there was only one mother, but lower the age to 200,000 years (cf. Newsweek, January 11, 1988).
God had given to Adam and Eve, our first parents, three levels of gifts: 1) basic humanity, consisting of a body and soul, with mind and will. Each has within it certain natural drives and needs. No one of these is evil in itself, but without the help of some added gift to coordinate them, they tend to get out of order, to rebel. 2) God gave to our first parents an added gift, which is just such a coordinating gift, which made it easy to keep each drive in its place. (It is sometimes called the gift of integrity). When Adam and Eve sinned, the lower flesh began to get out of line, to rebel. Hence Adam felt the need of cover; before the fall, he did not feel that, for the flesh was easily docile. God gave them also exemption from physical death, which otherwise would be natural to a being composed of parts, body and soul, which can come apart, and so die. 3)
He gave them the life of grace, a share in His own life, which made the soul basically capable of the vision of God in the life to come.
God clearly intended they should pass on all thee gifts to their children, including us. Through the narrative of the forbidden fruit, however, the Sacred author tells us that God gave our first parents some kind of command, whether it was about a tree or something else. Whatever it was, they violated His orders, and fell from His favor, losing sanctifying grace and the coordinating gift. Hence they transmitted to us only that basic humanity, without the other gifts.
Except for Jesus and Mary, all the descendents of Adam and Eve were conceived without sanctifying grace. Without that grace, the soul is not capable of the vision of God in heaven.
Each new baby arrives without the grace God willed it should have. An adult who sins mortally also lacks that grace: hence both can be said to be in the "state of sin", they lack the grace they should have, except that the adult is that way by his own fault, the baby without any fault. John Paul II explained, in a General Audience of October 1, 1986: "... it is evident that original sin in Adam's descendants has not the character of personal guilt. It is the privation of sanctifying grace... ." Privation means the lack of what ought to be there. So when we speak of transmission of original sin, it would be more accurate to speak of non-transmission of sanctifying grace.
Original sin also resulted in a darkening of the mind and weakening of the will, in comparison to what it might have been. Hence John Paul II also said in a General Audience of October 8, 1986: "According to the Church's teaching it is a case of a relative and not an absolute deterioration, not intrinsic to the human faculties . . . not of a loss of their essential capacities even in relation to the knowledge and love of God."
In other words, original sin took our race down only to the essential level, the first level we described. It did not make it positively corrupt, surely not totally corrupt as Martin Luther thought.
Right after the fall, God promised to send a Redeemer. God said to the serpent in Genesis 3:15: "I will put enmity between you and the woman, between her descendants and yours. He will strike at your head, you will strike at his heel." The Church, as did the Jews, inteprets this as a prophecy of the Messiah.