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Flashcards in Darwinism Deck (10)
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Theory of Natural selection originated at which island

Which birds?

The Galapagos Islands

13 types of Finches due to drought light beak couldn't survive.


which Book and year in which his theory was published?

On the Origin of Species



no. of postulates, Truth and inferences?

5 Postulates
3 truth
2 inferences


Explain the 3 truth and 2 inference.

First truth was that the reproductive capacity of animals and plants is very high. (By Alfred Wallace)

Second truth was that the population of a species remains more or less same or constant for every generation.

First inference drawn from both was that there would be struggle for existence.

Third truth was that variation recur universally.

Inference drawn from 1st and 3rd was that Nature selects only the fittest one to survive.


Postulate of Darwin

1. Overproduction: Species tends to over-produce.

2. Struggle for existence: Population increases in geometrical ratio whereas food increases in arithmetical ratio, hence there's a struggle for existence.

3.Variation: Everlasting competition compels organism to change according to the conditions so that they can utilize the natural resources and can survive successfully.

4. Natural selection or Survival of the fittest: Due to the struggle for existence, only those can survive who exhibits variations that are more beneficial in hardships.

5. Origin of species: he summarized above 4 in one heading "origin of Species by NS" Said as a result of struggle for existence, variability and inheritance, the successive generation tend to become better adapted to their environment. Adaptations are accumulated and ultimately leads to emergence of new species.


NS diagram

Consequences- Adaptation and evolution

Precondition- reproduction, inheritance, competition, variation.


types of NS and graph of evolution

Directional selection (Beak birds- Finches)

Stabilizing selection(Moderate traits appears rather extremes of two species; skin color changes to a common color in same region)

Divergent or descriptive selection (evolves in two different species)


Example of NS operating

Haemoglobin :
sickle cell hemoglobin (HbS) has decrease O2 holding capacity but Helps in fighting Malaria. And it decrease in generation of people who moved to temperate region.

Pepper-moth: 2 color White and Grey
Earlier white were more predated, after industrial revolution all white got camouflaged in black, now grey were more predated.



1. If nature is selecting phenotypic traits, then why are their variations

2. Nature is eliminating, hence elimination process.

3. NS acts on the variation but was unable to explain from where the variation comes.

4. if selecting only useful then what about vestigial organs like appendix

5. Didn't differentiated between somatic and germinal variation, considered all variation as heritable.

6. NS doesn't explain evolution of terrestrial from aquatic forms.

9. Didn't explain the mechanism of inheritance,

10. Even though criticized Lamarck's theory of use and disuse, he adopted it for explaining variations.


Difference with Lamarckism

D: Deals with vertical and horizontal aspects of evolution.
L: Concentrated more on Vertical aspects of evolution.

D: Based on evolution by common descent, i.e. life evolved from a common descent.
L: no such mention

D:emphasizes diversity due to struggle for existence and favorable variations.
L: Considered individuals as the unit of evolution.

D: Considers Population as unit of evolution
E: considers individuals as unit of evolution.

D: emphasizes modification of population
L: Emphasizes modification of individual.

D:Emphasizes that nature selects organisms in a population for evolution.
L: Emphasizes that nature directs organism for evolution.