( Creation-The man perfection )

Human evolution begins by fertilization ,
a process through which spermatozoon from
man is fused with ovum from woman to produce
the zygote.Although fertilization takes place
in a short period,it includes several stages,
in a very brief classification , sperm passes
through three stages to complete
fertilization :

1 - it passes a route to reach ovum and
penetrate through its corona.

2 - penetration to the translucent pant of
the ovum .

3 - amphimixis ) the union of the sperm and
ovum ).

Following fertilization , the zygote moves
towards uterus and along its route it bears
consecutive clevages the result of which is
augmentation of the number of embryonic
cells.The first embryonic division takes
place about 30 hours post fertilization.
After about 3 days and in 12 to 16 cell
stages zygote reaches the uterus . After
spending a few days in a free condition
in the uterus,in days 5th and 6th it begins
to implant in the uterine mucous memberan
and at this stage the cellular mass which
is called Blastocyst is completely lined
under the inner surface of the uterus and
the penetration zone is repaired.Complete
implantation usually takes about 2 weeks
to occur.

The required time for the evolution of zygote
to a complete fetus is called the Pregnancy
Period.This period for a quite matured
fetus is 280 days or 40 weeks after last
menstruation or exactly 266 days or 38 weeks
after fertilization pregnancy stages are
usually divided into three general periods :

1 - Preembryonic period :
During this period which includes the three
weeks post-fertitization , implantation is
completed.At the end of this period embryo
resembles a flat plane in the length of one
millimeter.This period is the beginning of
differentiation of organs and tissues.

2 - Embryonic period :
This period lasts up to the eighth week.
At this period the embryo has a spherical
form.The face begins to form;eyes,ears,and
nose appear and fingers and thumb develop.
At the beginning of this stage the embryo
has a tail that is gradually lost through
fetal development.All body organs form and
differentiate from each other.At about the
middle of the third week that human embryo
is no more able to provide its alimentary
needs through diffusion , the circulatory
system appears.During the 4th to 7th week
heart,with its four cavities appear.At the
end of this period , the embryo measures
about 2.5 cm. In length and weighs about
one gram and has a complete human shape
and is called fetus.At this stage,primary
signs of pregnancy appear in the mother.

3 - The fetal period :
This period is extended from the beginning of
9th week until delivery and is characterized
by rapid growth and maturation of organs and
viscera. Longitudinal growth is considerable
during the 3rd,4th,and 5th months , ) about
5 cm per month ( while during the lost two
months of pregnancy weight gain is more
conspicuous.At the beginning of this period
the embryo presents a human figure however,
the size of its head is disproportionately
larger than other organs and due to lack of
hypodermal fat it shows a slimbony
appearance . At the 5th month of pregnancy
fetal movements are easily perceived by the
mother . At 8th month,fat accumulates under
the skin and the fetus looses its bony
appearance.At the end of this period the
fetus is quite developed and pregnancy is
going to be ended.Soon labour begins.
It is worth mentioning that sometimes
due to concomitant exit of two ovums
and their fertilization by two sperms,
twins are born whose morphological and
genetic specifications show no particular
similarities and resemble two quite
different offsprings though they develope
synchronously and are born at the same time.
Sometimes however , at a very early stage
a zygot is divided into two quite separate
sections and in this case identical twins
are born who being originated from the same
cell quite similar to each other.