Transcript Evolution by Natural Selection

ENVIRONMENTAL
SCIENCE
Chapter 4 The Organization of
Life
4.2 Evolution
4.2 Evolution Objectives
• Explain the process of evolution by
natural selection.
• Explain the concept of adaptation.
• Describe the steps by which a
population of insects becomes
resistant to pesticide.
Introduction
• Organisms tend to be good at what
they do and designed for where
they live.
– For example, the chameleon can
change colors, use its tongue to shoot
out and grab insects, and hold onto
branches with specialized feet
– The chameleon’s eyes also turn on
turrets on its head so that it can watch
insects with a minimum of movement
Evolution by Natural
Selection
• In 1859, English naturalist
Charles Darwin published On
the Origin of the Species by
Means of Natural Selection
which proposed natural
selection as the mechanism by
which evolution occurs.
• Evolution, the concept that
species change over time, had
been around long before the
work of Darwin, however, this
explanation fit all existing
evidence and has survived
repeated experiments.
Evolution by Natural
Selection
• Darwin noted that species differ slightly from
one another in form, function, and behavior.
• He also noted that some of the differences
were hereditary – passed on from one
generation to the next.
• Darwin had no knowledge, however, of the
work of the Austrian monk Gregor Mendel
that would become the foundation for
modern genetics.
• Darwin also realized the role of
environmental pressures exerted on each
individual of a species.
Evolution by Natural
Selection
• Darwin proposed that some individuals,
because of certain traits, are more likely
to survive and reproduce.
• Natural selection is the term that Darwin
used to describe the unequal survival
and reproduction that results from the
presence or absence of particular traits.
• A trait is any characteristic that an
individual possesses.
• An adaptation is any trait that gives a
survival advantage to an individual.
Evolution by Natural
Selection
• Darwin viewed nature as selecting for certain
traits and organisms with those traits tended
to survive and reproduce.
– For example, lighter bones in birds allowing
them to fly, brighter feathers in some male
birds to attract a mate
• Over time, the population would include more
and more individuals with the advantageous
traits.
• As the population changes, so does the
species.
Evolution by Natural
Selection
• Coevolution is the
process in which two
species evolve in
response to long-term
interaction with one
another.
– For example, flowers
produce nectar to attract
insects which pick up
pollen on one plant and
transfer it to another
plant while feeding
Evolution by Artificial
Selection
• Many species of plants and animals have been
selectively bred through the ages for desired
characteristics.
• The selective breading of organisms by humans
for specific characteristics is called artificial
selections.
• Seed from the largest, sweetest fruit and the
most nutritious grains were repeatedly saved to
plant again for progressively more productive
crops throughout the last 10,000 years.
• Docile animals that produce much meat for
comparatively little effort were repeatedly bred
for domestication.
Summary of Natural
Selection
• There is variation within any species.
• Species tend to produce far more offspring
than are necessary for survival of that
species.
• There is a limited amount of resources
available.
• The combination of overproduction and
limited resources leads to fierce
competition over the available resources.
Summary of Natural
Selection
• Competition for resources results in
“survival of the fittest”.
– “Survival of the fittest” is the most
misunderstood phrase in science
– “Survival of the fittest” means that the
individuals who are the best adapted have a
better chance to survive and pass their genes
on to the next generation
– Those who have adaptations that give them an
advantage over others in the population still
are not guaranteed survival and reproduction
Summary of Natural
Selection
• After many generations under selective
reproductive pressures favoring some traits
and not favoring others, the gene pool shifts
to a point that it is distinctly different from the
original gene pool – hence a new species.
• Evolution, the fact that species have changed
over time, is not in debate in the scientific
community.
• The rate at which evolution occurs is,
however, open to a degree of interpretation.
The Peacock Story
Evolution of Resistance
• Human actions have actually resulted in
resistant pests and pathogenic bacteria.
• Resistance is the ability of one or more
organisms to tolerate a particular
chemical designed to kill it.
• Some individuals in the population may
have certain genes that allow them to
break the chemical down into a
harmless substance.
Evolution of Resistance
• Through our use of pesticides, we have been
promoting the evolution of more resistant pests.
• Over prescription and improper use of
antibiotics has led to many resistant forms of
pathogenic bacteria.
– For example, a pesticide may be sprayed onto corn to
kill grasshoppers
– The bulk of the grasshoppers die, but a few survive
– The survivors have some advantage over the others,
and are able to pass that trait on to the next
generation
– Each time the grasshopper population passes on its
genes to the next generation
– After many sprayings, the entire population may
become resistant to the pesticide.
References
• Chameleon Feeding http://imagedir.empas.com/imginfo.html?f=
V&c=3367&e=7
• Chameleon on Branch - http://www.peteonline.us/Images2/Kerry
• Bromeliad http://www.sjsd.k12.mo.us/Schools/mbio/p
hotos/1999Images/plant_life/pages/bromel
iad.htm
• Fennec Fox http://www.catbox.com/florian/photos/phot
o_ani.html
References
• The Origin of Species http://www.catbox.com/florian/photos/pho
to_ani.html
• Charles Darwin (younger image) http://www.froes.dds.nl/
• Charles Darwin (older image) http://4umi.com/image/people
• Insect Pollination http://faculty.uca.edu/~johnc/representati
ve_plant_groups.htm
References
• Peacock http://www.fcps.k12.va.us/KingsGlenES/
stuact/stupages/endanim/peacock.htm
• Resistant Bacterium Illustration http://www.bioteach.ubc.ca/Biodiversity/
AttackOfTheSuperbugs
• Methicillin Resistant Staphylococcus
aureus http://idinchildren.com/200403/frameset.
asp?article=ca-mrsa.asp