1. organisms produce more offspring than the environment can support
DARWIN’S THEORY AND THE MODERN SYNTHESIS
Darwin, an English naturalist, proposed natural selection as the mechanism of evolution
Darwin observed that
organisms produce more offspring than the environment can support
organisms vary in many characteristics
these variations can be inherited

2. Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted
Darwin saw natural selection as the basic mechanism of evolution
As a result, the proportion of individuals with favorable characteristics increases
Populations gradually change in response to the environment

3. This is called artificial selection
Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment
This is called artificial selection
Example of artificial selection in plants: five vegetables derived from wild mustard
Figure 13.4A

4. Example of artificial selection in animals: dog breeding
English springer spaniel
German shepherd
Yorkshire terrier
Mini-dachshund
Golden retriever
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog
Figure 13.4B

5. Thousands to millions of years of natural selection
These five canine species evolved from a single common ancestor species through natural selection
African wild dog
Coyote
Fox
Wolf
Jackal
Thousands to millions of years of natural selection
Ancestral canine
Figure 13.4C

6. Important terminology
Variation – Having genotypic and phenotypic differences in any population
Heritable – Any genetics that can be passed on to future generations
Fitness – Success of an organism’s individual adaptations and natural selection – usually measured by ability to reproduce.
Adaptation –traits that make an organism to thrive and reproduce in its environment.

7. 4 parts of Natural Selection

8. Scientists can observe natural selection in action
Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms
Example: camouflage adaptations of mantids that live in different environments
Figure 13.5A

9. Insecticide application
The evolution of insecticide resistance is an example of natural selection in action
Insecticide application
Chromosome with gene conferring resistance to insecticide
Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow
Survivor
Figure 13.5B

10. Sometimes, natural viruses or bacteria attack a population, killing those that have susceptibility to disease, leaving only that that are resistant to survive and reproduce.

11. Populations are the units of evolution
A species is a group of populations whose individuals can interbreed and produce fertile offspring
Human populations tend to concentrate locally, as this satellite photograph of North America shows
The modern synthesis connects Darwin’s theory of natural selection with population genetics
Figure 13.6

12. Adaptive change results when natural selection upsets genetic equilibrium
Natural selection results in the accumulation of traits that adapt a population to its environment
If the environment should change, natural selection would favor traits adapted to the new conditions
Because of this, it is populations, NOT individuals, that are theorized to evolve or change over time.
Today, evolution is a term used to describe biological change over time.