1. DARWIN & NATURAL SELECTION
Lecture #29
DARWIN & NATURAL SELECTION
Part 1
Ms. Day
Honors Biology

3. Darwin made two major points in his book called Origins of Species:
1. Many current species are descendants of ancestral species
2. Natural selection is HOW EVOLUTION occurs (current “Theory of Evolution”)

4. Resistance to the Idea of Evolution
The Origin of Species = Darwin’s book
Shook the deepest roots of Western culture
Challenged a worldview that had been prevalent for centuries
Earth ONLY ~6000 yrs old
It was unchanging!!!!

5. Lamarck’s Theory of Evolution (1809)
Lamarck hypothesized species change (evolve) over time because of:
use and disuse and
inheritance of acquired traits
The mechanisms he proposed are unsupported by evidence

6. Lamarck’s Theory of Evolution
Idea called Use and Disuse
If a body part were used, it got stronger
If body part NOT used, it deteriorated/disappeared

7. inheritance of acquired traits
Will his kids be born with big muscles because he has them?

8. WILL THE OFFSPRING BE NICELY PRUNED?

9. Charles Darwin LOVED nature
Sails on HMS Beagle at 22 and voyaged around world
Noted flora and fauna on islands off of South America
Contributions of Lyell, Hutton and Malthus lead him to his mechanism for evolution
species change through natural selection

10. The Voyage of the Beagle
Collected specimens of South American plants and animals
Observed adaptations of plants and animals that lived many different environments
Main focus = Galápagos Islands near the equator west of South America

11. The Galapagos Islands Small group of islands west of South America
Very different climates
Animals on islands unique

12. Darwin returned 5 years later in 1836
NORTH
AMERICA
SOUTH
AFRICA
EUROPE
AUSTRALIA
PACIFIC
OCEAN
ATLANTIC
England
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Galápagos
Islands
Darwin in 1840,
after his return
HMS Beagle in port
Equator
Tasmania
New
Zealand
Andes
Darwin returned 5 years later in 1836

13. Darwin’s Focus on Adaptation
Adaptation= a change in structure or habits, often inheritable to improve survival & reproduction in particular environment
A trait that allows you to live/reproduce better in a certain environment
Acts on variation in population
EXAMPLE
Finches (birds) on Galapagos islands resembled the mainland finch
BUT…Finches had different types of beaks adapted to their type of food gathering

14. LE 22-6
Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.
Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground.
Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.

15. Darwin’s Overall Observations
The # of organisms of each species will increase
In nature, populations tend to remain stable in size
Environmental resources are limited

16. More of Darwin’s Observations
5. Populations have variation
no 2 individuals being exactly alike
Much of this genetic variation between individuals is inheritable and can be caused by MUTATION
Variation is RANDOM!!!

17. Darwin’s Overall Conclusions
More individuals are made than can be supported by the environment leads to a struggle for existence among individuals
Only a fraction of offspring survive each generation
Survival of the Fittest

18. Darwin’s Conclusion
2. individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment leave more offspring than less fit individuals
Called FITNESS (survival and reproduction)
High survival = more offspring = more fit

19. Darwin’s Conclusion Key mechanism to evolution Natural Selection
SLOW, not random process causing some traits to become more or less common in a population
Acts on PHENOTYPES (adaptations)  influences GENOTYPES
Organisms best adapted to environment  survive  give genetic traits to future generations while those less adapted tend to be eliminated
Key mechanism to evolution

20. 3 Modes of Natural selection
Directional selection favors individuals that are one type of true bred (Ex: favors RR or rr)
Disruptive selection favors both type of trued breds (Ex: Favors RR and rr)
Stabilizing selection favors heterozygotes and acts against true breed phenotypes
(Ex: Favors Rr)

21. LIGHT/DARK ROCK HABITAT MEDIUM COLOR ROCK HABITAT

22. 3 Types of Natural Selection

23. Video: How Does Evolution Really Work?
Video: How Does Evolution Really Work?

24. Darwin’s Descent with Modification
refers to idea that all organisms are related and came from a common ancestor
the history of life is like a tree

25. Darwin’s 1st Idea: Evolution
What is evolution?
A change over time in the genetic combination of a population  give rise to biodiversity
Darwins definition of evolution = Descent with modification
Darwin’s 2nd Idea: Natural Selection
If an environment changes over time, natural selection may result in adaptation to these new conditions  new species can also evolve

26. Evidence for Evolution by Natural Selection
HOW DO WE KNOW EVOLUTION WORKS?
PPT Lecture #29: Part 2

27. Evidence for Evolution http://www. sumanasinc
Homology
a similarities in characteristic traits resulting from common ancestry
Anatomical Homologies
anatomical resemblances that represent variations on a structural theme present in a common ancestor
Called HOMOLOGOUS STRUCTURES
Same development, different function

28. LE 22-14
Human
Cat
Whale
Bat

29. 3. Vestigial organs
remains of structures once important in organism’s ancestors
Example: tailbones in humans, appendix, wings on ostrich, wisdom teeth in humans

30. 4. Comparative Embryology

31. Similar genes (DNA), RNA or amino acid sequences
5. Molecular Homologies
Similar genes (DNA), RNA or amino acid sequences
Example
genes shared among organisms inherited from a common ancestor
Ex #1: Homeobox is a DNA sequence in genes that regular development in plants, animals and fungi

32. Human Rhesus monkey Mouse Chicken Ex #2: Amino Acid/ Frog
LE 22-16
% of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Species
Human
100%
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Ex #2: Amino Acid/
Protein sequence
Frog
54%
Lamprey
14%

33. 6. Biogeography the geographic distribution of species Sugar Glider
Marsupial
Flying
Squirrel
Eutherian
(placental)
Some similar mammals that have adapted to similar environments have evolved independently from different ancestors

34. 7. Fossil Records 8. Field Studies
Paleontologists have discovered fossils of many transitional forms
Shows variety on organism across time
8. Field Studies

35. Key Concepts
What is the raw material necessary for the mechanism of Natural Selection?
Heritable variations
What is the smallest unit of evolution?
Populations (NOT individuals)
Darwin incorporated Lyell’s gradualism into biological evolution combined with Malthus’ observations regarding populations

36. What is a “theory” is science?
summarizes a hypothesis(es) that have been supported with repeated testing
If enough evidence accumulates to support a hypothesis, it moves to the next step—known as a theory—in the scientific method and becomes accepted as a valid explanation of a phenomenon
a theory is an explanation or model based on observation
theories can be proven or rejected, just like hypotheses.

37. What is a “theory” is science?
Scientific definition of theory is different from everyday meaning
non-scientific context of “theory” implies that something is unproven or speculative
Scientific definition refers to a comprehensive explanation of some aspect of nature that is supported by a vast (A LOT) body of evidence (data).

38. Is Evolution JUST a THEORY??? Is it SCIENCE based?
Video #1: Isn’t Evolution Just a Theory?

39. Some Cool Evolution Videos…
Poison Newts
Camouflage “Leaves”
Evolution of the Eye
Why Does Evolution Matter Now? (Video #6)