Amount of information available to different species |
Among all
living species, there is a special one: ours. This has been said since
antiquity, and has only been questioned in the last half century. Many
biologists argue that the human species is one among many, that it cannot be
considered superior to any of the others, either bacteria, insects, or other
mammals.
There is,
however, a quantitative and perfectly objective
criterion that makes it possible to prove that the human species
is unique, completely different from all others: the
amount of information that each individual can handle.
For
unicellular beings, the only information available to each individual is their
own genome, which is easy to quantify: their bit value is approximately equal to
twice the number of nucleotides in their genome. For viruses, from 10 to
50 kbits; for bacteria, up to 10 Mbits; for a unicellular eukaryote, up to 25
Mbits.
If we move
to multicellular animals and plants, the size of the genome increases, and with
it the amount of information it contains: about 200 Mbits for a nematode, up to
several Gbits for vertebrates. For man it is estimated at about 6 Gbits, not
much larger than the genomes of other mammals. In fact, the living being with the largest
genome happens to be a fish.
In addition
to the genome, vertebrates have a second source of information: their nervous
system, especially the brain. The total amount of information contained in a
brain is estimated at about 10 kbits for amphibians, 10 Gbits for reptiles, 200
Gbits for mammals.
Here man is
unique: in proportion to the human body, our brain is larger than that of any
other living species and is capable of storing no less than 10 Tbits (10 trillion
bits), 50 times more than most mammals and a thousand times more than our own
genome. It can be said that, with man, life crossed a critical point. For the first time in history, a single individual is able to
reach such levels of information handling.
Five
thousand years ago, with the invention of writing, man crossed a new critical
point, a consequence of the previous one. We have become the only species with a
third source of information, a memory external to our body. With the arrival of
computers and Internet, this information has been made available to everybody and
is still growing. Currently it is estimated that it has exceeded 100 exabits (100
quintillion bits, or 1020 bits: one followed by twenty zeros). Every
human being, apart from what is contained in the brain, has access to extra information
ten million times greater, as if we were
connected with ten million brains apart from ours.
The
attached figure summarizes this and combines (on a logarithmic scale) all
sources of information available at any time for the species capable of
handling most information, depending on the time elapsed from the origin of
life to the apparition of the said species, in billions of years.
C.S.Lewis |
Manuel Alfonseca
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