Evolution and Natural Selection

1. Day 13 October 21st Chapter 8
Dr Amy B Hollingsworth
The University of Akron
Fall 2014

2. Most agricultural pests evolve
resistance to pesticides.
How does this happen?
Winners versus Losers – the losers get
removed from the population

3. Removing the Losers

5. “Survival of the Fittest”
 Reproductive success
 Fitness
• a measure of the relative amount of
reproduction of an individual with a particular
phenotype, as compared with the
reproductive output of individuals with
alternative phenotypes

6. Fruit Fly Example
 One fly carries the genes for a version of a
trait that allows it to survive a long time
without food.
 The other fly has the genes for a different
version of the trait that allows it to survive
only a short while without food.
 Which fly has the greater fitness?

7. The alleles carried by an individual
with high fitness will increase their
market share in a population over
time and the population will evolve.

8. There are three important elements to
an organism’s fitness:
1. An individual’s fitness is measured
relative to other genotypes or
phenotypes in the population.

9. There are three important elements to
an organism’s fitness:
2. Fitness
depends on the
specific
environment in
which the
organism lives.

10. There are three important elements to
an organism’s fitness:
3. Fitness depends on an organism’s
reproductive success compared to other
organisms in the population.
•If you are sterile, and can never have babies, your fitness is ZERO
•On the other hand, if you inherit an allele that gives you a trait that
causes you to die at half the age of everyone else, but also causes
you to have twice as many offspring as the average while you are
alive, your fitness is increased.

11. "Survival of the fittest" is a
misnomer.
Why?

12. 8.12 Organisms in a population can become
better matched to their environment through
natural selection.

13.  Adaptation—the process by which
organisms become better matched to
their environment and the specific
features that make an organism
more fit—occurs as a result of natural
selection.

14. 8.13 Natural selection does not lead to
perfect organisms.

15. Why doesn’t natural selection lead
to the production
of perfect organisms?

16. Factors that Prevent Populations from
Progressing Inevitably toward Perfection
1. Environments change quickly.
2. Variation is needed as the raw material of
selection.
3. There may be multiple different alleles for a
trait, each causing an individual to have the
same fitness.

17. 8.14 Artificial selection is just a
special case of natural selection.
Apple growers - green, yellow, red, tart, sweet, large, and small.

18. 8.15 Natural selection can change the
traits seen in a population in several ways.

19. Directional Selection
Individuals with one extreme from the range
of variation in the population have higher
fitness.
The result of such selection
is not surprising: between
1920 and 1945, average milk
production increased by
about 50% in the United
States. Farmers only let the
cows with lots of milk breed

20. So, could this happen in nature?

21. How is medical technology undoing
the work of natural selection in optimizing
the number of babies
with normal birth weights?

22. Stabilizing Selection
Individuals with intermediate phenotypes are most fit.

23. 22 lbs – mom was diabetic
Born preemie at 22 weeks
Weighed less than 10 oz.

24. Should we save every baby born?
1. Yes, we should try to save every baby –
human or animal.
2. Yes, we should save every human, but not
try to save animal babies
3. No, We should only let the strongest
animals and humans – the healthy ones –
survive.

25. Disruptive Selection
Individuals with extreme phenotypes experience
the highest fitness, and those with intermediate
phenotypes have the lowest.

26. 8.16 Natural selection can cause the
evolution of complex traits and
behaviors.
Look at the betta fish!

27. 1954, William Thompson trained a group of rats to run through a maze for a food reward

28. How can a wing evolve if 1% of a
wing doesn’t help an organism fly or
glide at all?

29. Often, structures
appear because
they serve some
other purpose.
Functional Shifts

30. Biggest wings – hottest regions?

32. It is indeed remarkable that this theory
[evolution] has been progressively accepted
by researchers, following a series of
discoveries in various fields of knowledge.
The convergence, neither sought nor
fabricated, of the results of work that was
conducted independently is in itself a
significant argument in favor of this theory.
—Pope John Paul II, 1996

33. Five primary lines of evidence:
1. The fossil record
2. Biogeography
3. Comparative anatomy and embryology
4. Molecular biology
5. Laboratory and field experiments

34. 8.17 The fossil record
documents the process of
natural selection.
Although it has been central to much documentation of the
occurrence of evolution, it is a very incomplete record

36. In Darwin’s
time, it was
assumed
that the
deeper
down in the
earth a
fossil was
found, the
older it was.
“Relative
Dating”

37. Many branches, not just a straight line
Happened in North America 55 million years ago

38. First found in
northern Canada
and estimated at
375 million years
old, Tiktaalik
fossils appear to
represent a
transitional
phase between
fish and land
animals.

39. 8-18. Geographic patterns of species’
distributions reflect their evolutionary
histories.

40. History Matters
 Who arrived first?
 Are numerous different habitats available?
In Hawaii, it appears that a finch-like descendant of the
honeycreepers arrived 4-5 million years ago and rapidly
evolved into a large number of diverse species.
The same process has occurred and continues to occur in
all locales, not just on islands.