Origin of Species - Darwin Evolution_chp 1

1. Origin of Species

2. Evolution
Charles Robert Darwin (1859)- origin of species by natural selection
1)Species arose from common ancestor (descent with modification)
2)Mechanism is natural selection
Population can change over generations if individuals that possess
certain heritable traits leave more offspring-results in evolutionary
adaptation.
Change in genetic composition over time-new species
Fossil records can be used to test the evolutionary theory

3. Early theories
• Aristotle (384-322 B.C)- species is fixed
Scala nature (scale of nature)-Each form of life is perfect and
permanent and could be arranged on a ladder, or scale of increasing
complexity
Carolus Linnaeus (1707-1778)- founder of taxonomy: instead of linear
hierarchy , he adoped nested classification system (grouping together)
(pattern of creation)

4. Catastrophism
• Most fossils are found in sedimentary rocks (formed from sand and
mud that settle to the bottom of water)-new layer covers old one.
• Georges Cuvier (1769-1832):
1) deeper the strata more dissimilar the fossils are from current form
of life
2) Some species appear and some disappear
Catastrophism : confined to local geographic regions

5. Gradualism
• James Hutton, in 1795: Earth’s Geological change can take place
through the cumulative effect of slow but continuous
processes.
• Charles Lyell- incorporated this into a theory as uniformitarianism.
• Darwin reasoned if that is the case, earth must be older than 6000
years and similar process can act on living organism

6. Darwin’s voyage-HMS Beagle
• Journey began in 1831 with the mission of charting poorly stretches
of south American coastline.

7. OBSERVATIONS
• Various adaptation of plants and animals
• Resemblance of species living in particular region: organisms in
tropic region of south America resembles temperate region of
south America more than the tropic regions of Europe.
• Fossils also resemble living organism of that continent.
• Geological changes (volcanic eruption in Chile)-Marine organism in
Andes mountains
Galapagoas Island: Finches were unique to some island, some are
distributed to one or more island.
Adaptation to environment and origin of new species is related!!!

8. Adaptation to environment

9. • ALLFRED RUSSEL WALLACE (1823-1913)-Developed similar theory
and send the paper to Darwin
“ORIGIN OF SPECIES”-1859

10. • Earnst Mayr dissected Darwin’s theory into 3 inferences and 5
observations:
• OBSERVATION #1: All species have such great potential fertility that their population size
would increase exponentially if all individuals that are born reproduced successfully.
• OBSERVATION #2: Populations tend to remain stable in size, excepting seasonal
fluctuations.
• OBSERVATION #3: Environmental resources are limited.
• INFERENCE #1: Production of more individuals than the environment can support leads
to a struggle for existence among individuals of a population, with only a fraction of
offspring surviving each generation.

11. • OBSERVATION #4: Individuals of a population vary extensively in their characteristics; no
two individuals are exactly alike.
• OBSERVATION #5: Much of this variation is heritable.
• iNFERENCE #2: Survival in the struggle for existence is not random, but depends in part
on the hereditary constitution of the individuals. Those individuals whose inherited traits
best fit them to their environments are likely to leave more offspring than less fit
individuals.
• INFERENCE #3: This unequal ability of individuals to survive and reproduce will lead to a
gradual change in a population with favorable characteristics accumulating over the
generations

12. Artificial selection
• Artificial selection is the identification by humans of desirable traits in
plants and animals, and the steps taken to enhance and perpetuate
those traits in future generations

13. Can predation pressure selects for size and age
of maturity?
Dr. Reznik and Endler

14. Drug resistant HIV
-3TC: Blocks reverse transcriptase
-Natural variant that is resistant to
3TC have no advantage, replicate
slower

15. Important points to note
• Individuals don’t evolve, population do.
• Natural selection can amplify or diminish only heritable traits.
• Trait that is favourable in one situation may be detrimental or useless
in another.

16. Explanation for other observations
• Homology : Similarity resulting from common ancestry
Anatomical homologies

17. Anatomical homology- Vestigial organs
Remnants of structures that serve
important function in the organism’s
ancestors

18. Homology at molecular level

19. Biogeography
• Closely related species tend to be in a same geographic region (same
ecological niches in different region may be occupied by similar
looking but very different species)
Convergent
evolution

20. Overview
-Darwins Origin of species
-Earlier theories preceding origin of species
-Examples of Natural selection
-How anatomical homology and convergent evolution is explained by
Darwin’s view of life