Biology Reference
In-Depth Information
developed a totally probabilistic philosophy, according to which
randomness is an underlying factor in the world. He speaks of a
universe of propensities (Popper, 1992) and defines probability as
a disposition or propensity of the phenomena themselves. Such a
philosophy is in complete opposition to essentialism which main-
tains that things are determined by their essences (see this chapter,
ยง2.2.3). In developing the subject later, we shall merely define
deterministic and probabilistic systems in the usual way depending
on whether the probability of the events is equal to 1 (determinis-
tic) or between 0 and 1 (probabilistic). It is important to note that
in this framework defined by the theory of probabilities, there is
unity among natural phenomena, because there is no qualitative
difference between determinism and probabilism. Determinism is
the limiting case for probabilism when probability is equal to 1.
2.2
Errors related to using probability
Opinions of the area covered by the idea of chance are often some-
what vague. The mathematical theory of probability appeared in
the 17th century but events subject to chance had already been
described through other concepts before that. Those earlier ways of
looking at things have not totally disappeared, and still cause ambi-
guities which are the source of errors that need to be eliminated
before analysing biological problems.
2.2.1
Probability does not deny causality
One of these errors is to believe that a probabilistic phenomenon,
often called indeterministic, does not have a cause. The example of
the game of heads or tails shows that this is false. There is indeed
a cause, tossing the coin, with two possible results. The word 'cause'
means the conditions, in the widest sense, of the random event.
A genetic mutation is, for example, a random event. The frequency
of genes mutating is determined by the structure of the DNA and the
presence of mutagenic chemical agents. It varies depending on the
conditions in which the chromosomes find themselves. The probability
