1. Jane Choi
B IB Biology HL
NATURAL SELECTION

2. Natural Selection: the non-random process by which
biologic traits become either more or less common in
a population as a function of differential
reproduction of their bearers.
Natural Selection= A key mechanism of Evolution

4. CHARLES DARWIN’S ORIGIN OF SPECIES
Some kinds of organisms survive better in certain
conditions than others do; such organisms leave more
progeny and so become more common with time. The
environment thus “selects” those organisms best adapted
to present conditions. If environmental conditions
change, organisms that happen to possess the most
adaptive characteristics for those new conditions will
come to predominate.

5. Observation Deduction
Organisms vary- there are differences between
individual organisms even if they are members of
In the struggle for existence, the less well-
the same species. These differences affect how well
adapted individuals will tend to die and the
suited or fitted an organism is to its environment
better adapted will tend to survive. This is
and mode of existence. This is called adaption.
natural selection
Some individuals are better adapted than others
because they have the favorable variations.
Because the better-adapted individuals
survive, they can reproduce and pass on
their characteristics to their offspring. The
greater survival and reproductive success of
Much of the variation between individuals can be these individuals leads to an increase in the
passed on to offspring – it is inheritable. proportion of individuals in the population
that have the favorable variations. Over the
generations, the characteristics of the
population gradually change- the evolution
by natural selection.

6.  As a result of the natural selection, the genetic variation
within a population of organisms may cause some
individuals to survive and reproduce more successfully
than others.
 Natural selection acts on the phenotype, but the genetic
basis of a phenotype that gives a reproductive advantage
will become more common in a population.

7. 5.4.7 EXPLAIN HOW NATURAL SELECTION
LEADS TO EVOLUTION
 Natural selection is a process (not a thing) which requires:
 production of variation. (the random part)
 the actual selection (non-random)
 When a population evolves there is a cumulative change in
the heritable characteristics of the population.
 Natural selection can act on a population without speciation
occurring.
 In effect the genetic profile of the population is adapting to
changes in local conditions.
 Every phase in the process of evolution is affected by
variation and by selection.