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AP Biology

7.2 Natural Selection

Natural selection

Evidential support for evolution and common ancestry

7.2: Natural Selection
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Cactus ground finch
Large ground finch (seeds) (cactus fruits and flowers)
JJ
Vegetarian finch (buds) Woodpecker finch (insects)
I. Introduction to Natural Selection
Natural selection is a mechanism of evolution proposed by Charles
Darwin. It is the process by which individuals with advantageous traits are
more likely to survive and reproduce, leading to the gradual change
of a population over time.
II. Principles of Natural Selection
A. Variation
Within a population, individuals exhibit variation in their traits due
to genetic differences and environmental factors.
This variation is the raw material upon which natural selection
acts.
B. Heritability
Traits that confer a reproductive advantage are more likely to be
passed on to the next generation.
Genetic heritability allows advantageous traits to be inherited by
offspring.
C. Overproduction and Competition Populations have the potential to produce more offspring than the
environment can support.
This leads to competition for limited resources, where only a
fraction of offspring survive to reproduce.
D. Differential Survival and Reproduction
Individuals with advantageous traits are more likely to survive and
reproduce in a given environment.
This leads to an increase in the frequency of those traits in the
population over generations.
III. Evidence for Natural Selection
A. Fossil Record
Fossils provide evidence of extinct species and the gradual changes
in species over time.
Transitional fossils show intermediate forms that link different
groups of organisms.
B. Comparative Anatomy Homologous structures in different species suggest a common
ancestor.
Analogous structures in different species indicate similar
adaptations to similar environments.
C. Comparative Embryology
Similarities in embryonic development among different species
suggest a shared evolutionary history.
Embryos of different species often exhibit similar structures at
early stages.
D. Molecular Biology
DNA and protein sequence comparisons reveal evolutionary
relationships.
Similarities in DNA sequences indicate a more recent common
ancestor.
IV. Modes of Natural Selection A. Stabilizing Selection
Intermediate phenotypes are favored, reducing variation and
maintaining the status quo.
Example: Human birth weight, where extremes can be
disadvantageous.
B. Directional Selection
One extreme phenotype is favored, causing a shift in the population
over time.
Example: Peppered moths during the Industrial Revolution, where
dark-colored moths had a survival advantage in polluted
environments.
C. Disruptive Selection
Both extreme phenotypes are favored, leading to the division of a
population into two distinct groups.
Example: Beak size in Darwin's finches, where small and large beaks
were advantageous for different food sources. V. Adaptations and Fitness
A. Adaptations
Adaptations are traits that increase an organism's survival and
reproductive success in a particular environment.
They are shaped by natural selection and can be structural,
physiological, or behavioral.
B. Fitness
Fitness is a measure of an individual's reproductive success and
contribution to the gene pool of the next generation.
Fitness is relative and dependent on the specific environment in
which an organism lives.
VI. Conclusion
Natural selection is a fundamental mechanism of evolution that
leads to the adaptation and change of populations over time. It is supported by extensive evidence from various fields of study,
including paleontology, comparative anatomy, embryology, and
molecular biology.
Understanding natural selection is crucial for comprehending the
diversity of life and the processes that have shaped the natural
world.

7.2 Natural Selection

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7.2 Natural Selection

Can't find what you're looking for? Explore other subjects.

Knowunity is the # 1 ranked education app in five European countries

Knowunity was a featured story by Apple and has consistently topped the app store charts within the education category in Germany, Italy, Poland, Switzerland and United Kingdom. Join Knowunity today and help millions of students around the world.

4.9+

13 M

#1

950 K+

Still not sure? Look at what your fellow peers are saying...

I love this app so much [...] I recommend Knowunity to everyone!!! I went from a C to an A with it :D

The application is very simple and well designed. So far I have found what I was looking for :D

Love this App ❤️, I use it basically all the time whenever I'm studying