Richard Dawkins
Another aspect of the particulateness of the gene is that it does not grow senile; it is no more likely to die when it is a million years old than when it is only a hundred. It leaps from body to body down the generations, manipulating body after body in its own way and for its own ends, abandoning a succession of mortal bodies before they sink in senility and death.
The genes are the immortals, or rather, they are defined as genetic entities that come close to deserving the title. We, the individual survival machines in the world, can expect to live a few more decades. But the genes in the world have an expectation of life that must be measured not in decades but in thousands and millions of years.
In sexually reproducing species, the individual is too
large and too temporary a genetic unit to qualify as a significant unit of
natural selection.* The group of individuals is an even larger unit.
Genetically speaking, individuals and groups are like clouds in the sky or
dust-storms in the desert. They are temporary aggregations or federations. They
are not stable through evolutionary time. Populations may last a long while,
but they are constantly blending with other populations and so losing their
identity. They are also subject to evolutionary change from within. A
population is not a discrete enough entity to be a unit of natural selection,
not stable and unitary enough to be 'selected' in preference to another
population.
An individual body seems discrete
enough while it lasts, but alas, how long is that? Each individual is unique.
You cannot get evolution by selecting between entities when there is only one
copy of each entity! Sexual reproduction is not replication. Just as a
population is contaminated by other
populations, so an individual's posterity is contaminated by that of his sexual
partner. Your children are only half you, your grandchildren only a quarter
you. In a few generations the most you can hope for is a large number of
descendants, each of whom bears only a tiny portion of you—a few genes—even if
a few do bear your surname as well.
Individuals are not stable
things, they are fleeting. Chromosomes too are shuffled into oblivion, like
hands of cards soon after they are dealt. But the cards themselves survive the
shuffling. The cards are the genes. The genes are not destroyed by crossing-over,
they merely change partners and march on. Of course they march on. That is
their business. They are the replicators and we are their survival machines.
When we have served our purpose we are cast aside.
But genes are denizens of geological time: genes are
forever.
Note: This passages have been token from the author's book which is titled as " The Selfish Gene." page: 34-35
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