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The Tree of Life

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 :

Does death have any sense?

1997 Eduardo Diaz Diaz

Last updated: March 28th, 1997