Most contemporary biologists
assure that life has only emerged once on Earth. Every living being, if
a virus, bacteria, mushroom, plant or animal, descends from a unique common
ancestor.
The evidence provided by the
chemical characteristics of genetic material that determines the formation
of every living being, points at, without a doubt, towards that common
origin.
In each one of our cells we
contain sets of genes, grouped in chromosomes, that repeat the instructions
for constructing a living begin an unaccountable amount of times, also
detailing with care the characteristics of the biochemical functioning
of all of that being.
Many of those sets of instructions
are as identical in bacteria as in a turtle of even a human being.
The Family Tree that was expressed
before permits the classification of all living beings to be a practically
exact discipline.
An organism will be more related
with an other as they share more genetic material.
Even though the evolution of
species is produced thanks to the nucleic acids, it has been discovered
that their exists a process of constant change in the characteristics of
some of the chemical substances produced by the organism, which permits
the dating of the time at which a certain species separated from an other
or some common ancestor of various species that know constitute a family.
It really results impacting
to know that the approximate date, which is sometimes millions and even
billions of years ago, in which their lived a common ancestor of us and
a domestic animal, or the poor beast from which came the meat we are eating,
or in between any vegetable or microscopic organism that we could think
of. The British biologist Richard Dawkins points out some interesting dates
about this.
The last common ancestor between
men and chimpanzees lived as recently as five million years ago. The last
common ancestor between all anthropoids - men, gorillas, and chimpanzees
- and all the monkeys of the old and new continent (apes with a tail) lived
some 35 million years ago.
The last common ancestor between
us and the lemurides lived 40 million years ago. Our last common ancestor
with the carnivores (cats, dogs) lived some 60 million years ago. At about
65 million years ago their lived the last common ancestor between men and
whales, bats, horses, cows, elephants, and other mammals of this type.
At least 100 million years ago
their lived our last common ancestor with the insectivores (moles, hedgehogs).
The last common ancestor between men and kangaroos live 150 million years
ago, and 170 million years ago the last ascendancy of humans and platypuses.
Many years before, in the carboniferous
period, 320 million years ago, their lived the last common ancestor of
man and all birds and reptiles. At about 370 million years ago, in the
Devonian period, the last common ascendancy between humans and frogs died
out, and 420 millions years ago the last one between the scaled fishes
and ourselves disappeared. A "short" time before, 470 millions
years ago, the last common ancestor of all vertebrates died. About a billion
years ago (one thousand million) the last common ancestors of chordates
- ourselves - , arachnids, worms, insects, and, a little before, the last
one’s between insects and mollusks.
The last common ancestor between
a whale and a pea lived about 2 billion years ago, without a doubt, a unicellular
organism similar to bacteria. The oldest common ancestor of all lived about
3 billion years ago.
But not all agree that life
only originated once Earth and that all living beings constitute a single
family... which is sometimes not a happy one.
There are indications that at
least another type of life exists, which has an activity that has proven
to be very harmful against beings based on the chemistry of DNA like us.
According to the American pathologist
Lewis Thomas, one of the most terrible sicknesses of moderns times is caused
by microorganisms with a chemical base radically different to DNA.
More than two million people
worldwide are affected by some senile sickness. Individuals that suffer
sicknesses like Alzheimer’s and Jacob or Creutzfeld, have suffered an invasion
in their cerebral tissue by trillions of microorganisms similar to "slow
viruses", which have no nucleic acids but that can, nevertheless,
fabricate replicates of themselves. They are profoundly aggressive living
beings, with whom we are not related at all and with whom we don’t share
any ancestor.
It is almost certain that all of the life forms
that live on Earth today originated in the way described, but do we really
understand the concept of the long period of time that has gone by ever
since the origin of the universe and earthly life forms. Let's try to comprehend
such a concept by examining :
©
1997 Eduardo Diaz Diaz
Last updated: March 28th,1997
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