1. Lecture #33 DARWIN & NATURAL SELECTION 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 a the way in which 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 evolve through
use and disuse and
inheritance of acquired traits
The mechanisms he proposed are unsupported by evidence

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

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 inhabited many diverse environments
Main focus of geographic distribution of species = Galápagos Islands near the equator west of South America

11. The Galapagos Islands
Small group of islands 1000 km 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 hereditary, to improve survival and reproduction in environment
Adaptation to environment and the origin of new species  are closely related processes
EXAMPLE
Finches on the islands resembled a mainland finch
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
Left unchecked, 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
Individuals of a population vary in characteristics with no 2 individuals being exactly alike.
Much of this variation between individuals is inheritable.

17. Darwin’s Overall Conclusions
Production of more individuals 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
Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals
Called FITNESS
High survival = more offspring = more fit

19. Darwin’s Conclusion
Natural Selection
gradual, nonrandom process by which traits become more/less common in a population
Acts on PHENOTYPES (adaptations), which influences GENOTYPES
only organisms best adapted to environment tend to survive and transmit genetic traits to future generations while those less adapted tend to be eliminated
Key mechanism to evolution

20.
Video #4: How Does Evolution Really Work?

21. Darwin’s Descent with Modification
refers to idea that all organisms are related through descent from common ancestor that lived in the remote past
the history of life is like a tree

22. Darwin’s 1st Idea: Evolution
What is evolution?
All accumulated changes across successive generations in inherited characteristics of populations
A change over time in the genetic combination in a population  give rise to diversity
Darwins definition = 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

23. 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

24. LE 22-14
Human
Cat
Whale
Bat

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

26. 4. Comparative Embryology

27. 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

28. 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%

29. 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

30. Paleontologists have discovered fossils of many transitional forms
7. Fossil Records
Paleontologists have discovered fossils of many transitional forms
Shows variety on organism across time

31. 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

32. 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.

33. 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).

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

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