Biology Reference
In-Depth Information
that the car must maintain throughout the whole journey. If the
journey is travelled several times the car will cover the distance in a
constant time related to the speed set, affected by some greater or
lesser statistical variation depending on the driver, the car and the
conditions in which the journey is made (Fig. 2A). For example, on
a hill or when there is a violent gust of wind the car may adjust its
speed more or less easily depending on how powerful it is. The car's
behaviour is deterministic but there are internal disturbances to the
system, related to its physical characteristics, and external ones due
t
t2
t1
A : deterministic mechanism
with noise
variability before selection
t
t1
t2
t
variability after selection
B : intrinsically probabilistic mechanism
subjected to selection
F
IGURE
2. The difference between deterministic, probabilistic, and selective
mechanisms.
The car travels the distance in a time
t
which varies between
t
1
and
t
2
.
A:
Even if the behaviour were deterministic, there is always inevitable variability
(dotted line) in this travel time which is added to a constant time (solid line).
B:
In general, if the car adopts intrinsically probabilistic behaviour without a pre-
cisely set constant speed, the variability in its time to travel the distance will be
greater and will comply with a statistically different law. If this intrinsically proba-
bilistic behaviour is however, subjected to forced selection, the remaining variability
may be comparable to that of a deterministic mechanism. In this case, the two types
of mechanisms are difficult to distinguish, except by performing a more detailed
analysis.
