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(where the P(Y) region is active), nevertheless when their terminal region is recog-
nized by the liver specific miRNA, they activate a silencing process that prevents the
translation of this transcript, therefore the gene X cannot be expressed. Silencing is
a very complex process, studied some time ago in plants, which is very important in
gene regulation and defence against viral infections (often based on double-stranded
RNA vectors). Many biomolecular elements and complexes are involved in RNA si-
lencing (RNAase, Dicer, Risc-complex, and argonaute protein), which are activated
by the double RNA strands of miRNA paired to complementary target regions, and
eventually cleaved in the process.
4.6
Life Evolution
The following are Darwin's main arguments at the basis of his evolution theory
[125]. On putting them together, there follows a confutation of the fixity of biolog-
ical species over time (a mathematical analysis of natural selection was developed
by Fisher [131] who was also one of the founders of mathematical statistics).
•
Geology
Geology tells us that earth changes and consequently life environments can differ
dramatically in different epochs.
•
Fitness
Malthusian growth of biological populations shows that, when there is a compe-
tition for resources, individuals with characters which better fit the environment
have more chance of surviving.
•
Heredity
Genealogical evidence and breeders' experience show that the characters of par-
ents are transmitted to the offspring (at that time, Darwin was not aware of
Mendel's experiments).
•
Chance
The appearance of characters which are selected is not forced by their increased
fitness, but they occur freely by chance, and then they are kept by natural
selection.
The
Geology
argument was an important start of Darwin's reflection and its main
value was the correct temporal scale on which the dynamics of biological charac-
ters should be considered. Arguments
Geology+Fitting
imply
that
species change,
while
Heredity+Chance
imply
how
they do it. Darwin developed a theory where the
four statements above prove to be integrated in a coherent conceptual framework,
which he supported by means of the findings he collected during his famous scien-
tific journey. But, it is important to stress that the motivations for data supporting
his claims followed the logical analysis he started from. In this sense, we can com-
pare the intellectual strength of Darwinian theory of evolution, to Galieo's mental
experiment about falling bodies, which marked the birth of modern mechanics.
It is surprising that in the
Geology+Fitting+Heredity+Chance
argument, hered-
ity, which is the mechanism for transmitting biological information, represents also
the way in which biological innovation is realized by means of chance. Maybe, as
