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APPEARANCE OF DIPLOIDAL CELLS.
In the process of evolution and improvement of cellular molecular
structures, the time of sperm stay in the state of a double set of
chromosomes gradually increased.
The existence of a spermatozoon with single chromosomes has become
relatively short.
Without going into details, let's say the on-duty phrase that "this
created an evolutionary advantage."
So there were already full-fledged unicellular animals of the same type
as spermatozoa, only with a double set of chromosomes.
Further, we will call them spermoids.
Definition.
A spermoid is an animal cell, with a flagellum (or
several) as a sperm, for most of its life cycle is in the state of a
double (diploid) set of chromosomes.
At
the initial stages of evolution, the spermoid is simply a sperm with two
chromosomes.
Thesa.
The appearance of the first diploid unicellular animals,
close to the modern ones, occurred through the elongation of the stage
of a double chromosome set from the process of reproduction of primary
spermatozoa.
Later,
at one of the stages, it became possible to multiply an animal cell
(i.e., a spermoid) by doubling the number of chromosomes (already
already there were two) and then dividing into two new cells.
This division is
called mitosis.
Thus, both meiosis and mitosis arose at the stage of unicellular
organisms.
The first meiosis appeared and it was preserved forever, because it
created high adaptive possibilities.
Mitosis simply serves as a breeding without variation of the
genotype (except for crossing).
There
is a well-known dispute between different schools of biologists.
According to some, evolutionary change begins when the population falls
into unaccustomed conditions of existence.
New external factors act directly on the ontogenesis of individuals and
cause morphoses.
Morphoses represent a new material for natural selection.
If any of the newly appeared morphoses is able to exist under changed
conditions, then natural selection leads to genetic assimilation of this
morphosis.
Thus, evolution begins with a change in the environment and ends in the
genome.
Other scientists, followers of Darwin, view evolution as the
reverse sequence of events: from a new gene to a new ecosystem.
It
seems, and we think so, that in the light of the above, both are right.
The chromosome that lives inside the cell, although protected from the
influence of the external environment, but not 100%.
That is, a small reverse effect of the external environment on it
necessarily exists.
Therefore, on the one hand, random mutations of the chromosome itself
can be fixed if they are successful.
But on the other hand, changes outside create tension inside the cell,
which sometimes leads to the fact that: a) the cell weakens and becomes
uncompetitive b) to the forced mutation of the chromosome in the
direction of removing the external voltage.
c) the competitiveness of such an accidentally mutated
chromosome, which previously was consistently uncompetitive.
Recall
the law of physics: every system that is under external influence
behaves in such a way as to reduce this impact.
Summary: evolution is possible even under unchanging external
conditions.
The only driver of this evolution is random mutations, although they can
give out very progressive changes.
The consolidation of such mutations in the ecosystem depends on the
response of other members of the ecosystem.
Not every, even progressive mutation is able to gain a foothold, if in
parallel there are no suitable mutations of contacting species.
But when the external conditions change, the intensity of the mutations
increases and their direction is determined by the change in external
conditions.
You can also recall our long-standing reflections that there are no
stable states in Nature.
The ecological niches
are being filled.
Nobody knows the size and shape of these niches.
Yes there is biology.
That brightened in the head of a man (A.Parshin - "Why is not Russia
America?") And he realized that all the troubles in Russia are coming
from the climate. Truly so!
And what do you want to do with your favorite writers who have covered
the Russian reality?
After all, these writers are wrong!
Gogol, Chekhov - they are
wrong!
After all, like in India or Africa: jumped, ripped off a banana and you
are full.
And
we have to work half a day to feed ourselves.
They
hung a rag or leaves on their hips, and you're dressed.
And we -
work in the second half of the day for clothes.
In Europe, I built something, a building, a road, a bridge - and it
costs 100 years.
And we
have after the winter - a mandatory repair of everything.
More than three years without repair in our climate, no structure can
withstand! And favorite
writers laugh.
And the humorists roll off, why are we so clever, and so poor?
And we do not
understand, and humorists do not understand.
But the man
understood and we all became fools.
So in biology: how many theories seemed correct, intelligent, ingenious.
And look
wider - and complete nonsense.
Well, what natural selection?
Well, they eat sick, old and defective.
And everything else is very doubtful.
Gradually,
oxygen accumulated in the atmosphere.
In the oxygen atmosphere, all the processes went much more actively and
very complex molecular formations and multicellular organisms became
possible.
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