Natural selection is a process whereby organisms better adapted to their environment tend to survive and produce more offspring. There are three main types of natural selection: directional selection favors one extreme of a trait, disruptive selection favors both extremes of a trait, and stabilizing selection favors intermediate forms of a trait. Examples of natural selection in action include the evolution of different beak shapes in Galapagos finches and the increase of melanism in moths due to pollution. Sexual selection is a form of natural selection resulting from competition or choice of mates.

2. Usman
M.Phil Zoology Section B
Topic Of Presentation
NATURAL SELECTION
AND ITS TYPES

3. Natural selection described by
Charles Darwin.
Basic and fundamental
mechanism of the theory of
evolution.
The term was introduced in "On
The Origin of Species," in 1859.

4. The Natural Selection is a process, by which
organisms are better adapted to their
environment tend to survive and produce more
offspring.
A Natural Selection is a process that results in
the survival and reproductive success of
individuals or groups best adjusted to their
environment.
What is Natural Selection?

5. The process of natural selection relies
on a few Important Factors
Variation within a species is
necessary
Individuals must vary in
appearance or behavior
The variable traits must be
inherited by offspring
Factors

6. Competition
Since food and resources are limited
The offspring have to compete to survive
Darwin called it Struggle For Existence

7. ⚫ Galapagos Finches
⚫ Beak size and shape
adapted for specific type of
food
⚫ Their beaks evolved due to
natural selection.
⚫ Individuals with the right
shaped beak to reach the
food would survive.

8. There are the following types of natural
selection which affect the phenotypes of
individuals are:
Directional Selection
Disruptive Selection
Stabilizing Selection
Types of Natural Selection

9. ⚫ A type of Natural Selection
in which the phenotype of
the species tends toward
one extreme.
⚫ Occurs when natural
selection favors one
extreme of continuous
variation.
⚫ The favored extreme will
become more common .

10. ⚫ The frequency of the
melanic form of the
moth increased
⚫ Their darker coloration
provided camouflage
against the sooty tree
⚫ Had a higher survival
rate in habitats affected
by air pollution

11. ⚫ A type of natural selection
that removes individuals
from the center of a
phenotypic distribution and
causes the distribution to
become bimodal.
⚫ Occurs when natural
selection favors both
extremes of continuous
variation.
⚫ The two extreme variations
will become more common.

12. ⚫ Light-colored oysters are
more coloration
⚫ allow organism to match
its background
⚫ Dark-colored oysters blend
into the shadows cast by
the rocks
⚫ Intermediate-colored
oysters would be most
heavily preyed upon by the
crabs

13. ⚫ Removes individuals from
both ends of a phenotypic
distribution, maintaining
the same distribution
mean.
⚫ Occurs when natural
selection favors the
intermediate states of
continuous variation.
⚫ The intermediate states
become more common.

14. ⚫ Very light-colored or very
dark-colored oysters might
be more frequently preyed
upon by shore birds
⚫ Because they are more
obvious on the oyster bar
⚫ The intermediate colored
oysters become more
common

15. The different genders in a species exert forces on
each other that changes their appearance or traits.
✔ Natural selection favors traits that maximize
✔ The ability of an individual to compete
✔ Attract mates
✔ The ability to produce offspring
⚫
Sexual Selection

16. ⚫ The peacocks with the
showier feathers are able to
attract mates
⚫ Peacocks can fold up their
tails, in danger of predator
⚫ Peahens are much duller
and more camouflaged
⚫ They are the ones who
guard the eggs and chicks
⚫ Survival of the next
generation is very
important

17. A type of selection that involves altruistic
behavior
Occurs when natural selection favors a trait that
benefits related members of a group
✔ The protection of offspring
✔ Parent acts to preserve the gene pool of offspring
✔ At the expense of itself.

18. ⚫ Bees exhibit altruistic
behavior by spending
their lives serving the
hive
⚫ The worker bee does not
reproduce
⚫ Queen is able to produce
many more related
offspring

19. ⚫ Andersson, M. and L. W. Simmons. 2006. Sexual selection and mate choice. Trends Ecol.
Evol., 21: 154-165.
⚫ Brunnander, B. 2007. What is natural selection. Biol. Philos., 22: 231-246.
⚫ Gavrilets, S. 2004. Fitness Landscapes and the Origin of Species. Princeton Univ. Press,
41:978-691.
⚫ Haldane, J. B. S. 1992. The Cost of Natural Selection. Curr. Sci., 14: 612-625.
⚫ Mayr, E. 1997. The objects of selection. Proc. Natl. Acad. Sci., 94: 2091-2094.
⚫ Pust, J. 2001. Natural selection explanation and origin essentialism. Can. J. Philos., 31:
201-220.
⚫ Williams, G. C. 1966. Adaptation and Natural Selection. Princeton Univ. Press, 8: 86-93.
⚫ Lenski, R. E. 2017. What is adaptation by natural selection. PLoS One, 13: 100-105.