Here is Tertullian’s (name removed by moderator)ut on the subject, from about the beginning of the 3rd century.
SOUL AND BODY CONCEIVED, FORMED AND
PERFECTED IN ELEMENT SIMULTANEOUSLY
How, then, is a living being conceived? Is the substance of both body and
soul formed together at one and the same time? Or does one of them
precede the other in natural formation? We indeed maintain that both are
conceived, and formed, and perfectly simultaneously, as well as born
together; and that not a moment’s interval occurs in their conception, so
that, a prior place can be assigned to either. Judge, in fact, of the incidents
of man’s earliest existence by those which occur to him at the very last.
As death is defined to be nothing else than the separation of body and
soul, life, which is the opposite of death, is susceptible of no other
definition than the conjunction of body and soul. If the severance happens
at one and the same time to both substances by means of death, so the law
of their combination ought to assure us that it occurs simultaneously to
the two substances by means of life. Now we allow that life begins with
conception, because we contend that the soul also begins from conception;
life taking its commencement at the same moment and place that the soul
does. Thus, then, the processes which act together to produce separation
by death, also combine in a simultaneous action to produce life. If we
assign priority to (the formation of) one of the natures, and a subsequent
time to the other, we shall have further to determine the precise times of
the semination, according to the condition and rank of each. And that being
so, what time shall we give to the seed of the body, and what to the seed
of the soul? Besides, if different periods are to be assigned to the
seminations then arising out of this difference in time, we shall also have
different substances. For although we shall allow that there are two kinds
of seed — that of the body and that of the soul — we still declare that
they are inseparable, and therefore contemporaneous and simultaneous in
origin. Now let no one take offense or feel ashamed at an interpretation of
the processes of nature which is rendered necessary (by the defense of the
truth). Nature should be to us an object of reverence, not of blushes. It is
lust, not natural usage, which has brought shame on the intercourse of the
sexes. It is the excess, not the normal state, which is immodest and
unchaste: the normal condition has received a blessing from God, and is
blest by Him: “Be fruitful, and multiply, (and replenish the earth.)”
Excess, however, has He cursed, in adulteries, and wantonness, and
chambering. Well, now, in this usual function of the sexes which brings
together the male and the female in their common intercourse, we know
that both the soul and the flesh discharge a duty together: the soul
supplies desire, the flesh contributes the gratification of it; the soul
furnishes the instigation, the flesh affords the realization. The entire man
being excited by the one effort of both natures, his seminal substance is
discharged, deriving its fluidity from the body, and its warmth from the
soul. Now if the soul in Greek is a word which is synonymous with cold,
how does it come to pass that the body grows cold after the soul has
quitted it? Indeed (if I run the risk of offending modesty even, in my desire
to prove the truth), I cannot help asking, whether we do not, in that very
heat of extreme gratification when the generative fluid is ejected, feel that
somewhat of our soul has gone from us? And do we not experience a
faintness and prostration along with a dimness of sight? This, then, must
be the soul-producing seed, which arises at once from the out-drip of the
soul, just as that fluid is the body-producing seed which proceeds from the
drainage of the flesh. Most true are the examples of the first creation.
Adam’s flesh was formed of clay. Now what is clay but an excellent
moisture, whence should spring the generating fluid? From the breath of
God first came the soul. But what else is the breath of God than the vapor
of the spirit, whence should spring that which we breathe out through the
generative fluid? Forasmuch, therefore, as these two different and separate
substances, the clay and the breath, combined at the first creation in
forming the individual man, they then both amalgamated and mixed their
proper seminal rudiments in one, and ever afterwards communicated to the
human race the normal mode of its propagation, so that even now the two
substances, although diverse from each other, flow forth simultaneously in
a united channel; and finding their way together into their appointed
seed-plot, they fertilize with their combined vigor the human fruit out of
their respective natures. And inherent in this human product is his own
seed, according to the process which has been ordained for every creature
endowed with the functions of generation. Accordingly from the one
(primeval) man comes the entire outflow and redundance of men’s souls
— nature proving herself true to the commandment of God, “Be fruitful,
and multiply.” For in the very preamble of this one production, “Let us
make man,” man’s whole posterity was declared and described in a plural
phrase, “Let them have dominion over the fish of the sea,” etc. And no
wonder: in the seed lies the promise and earnest of the crop.
Also consider that over 50% of conceptions end up as spontaneous abortions…not really sure God would create all those souls only to have them lost before implantation, but hey, He’s the Boss. He can do what He likes.