1. Natural Selection
Section 7.5

2. The Theory of Evolution by Natural Selection
Learning Goal: To explore Darwin’s theory of natural selection.
Success Criteria:
I know I am succeeding when I can…
explain that natural selection favours the reproductive success of individuals with certain heritable traits called adaptations
explain that process of natural selections
use natural selection to explain adaptations of species in examples
This lesson will present the many forms of evidence that convinced Darwin that species had changed over time and that species appeared to share a common ancestry. The basis of his theory on the evolution of species.

3. The Theory of Natural Selection
natural selection (a.k.a. “survival of the fittest”): the way in which nature favours the reproductive success of some individuals within a population over others
the process of natural selection acting over thousands of generations could produce an unlimited variety of species

4. 5 Points of Darwin’s Natural Selection
Populations produce more offspring than can survive and reproduce.
Individuals within a population exhibit variability.
Some individuals have characteristics (adaptions) that give them a better chance of surviving and reproducing.
These traits, IF heritable, will become more common in the next generation.
The result of natural selection is a population better adapted to it’s environment.
all healthy populations produce far more offspring than could survive and reproduce
individuals within a population exhibit heritable variability
some individuals will have characteristics (adaptions) that give them a better chance of surviving and reproducing than others
if these characteristics are inherited, then the traits of the favoured individuals would become more common in the next generation

5. An Example of Natural Selection
the large-billed ground finch of the Galapagos islands evolved from an ancestral species that possessed a much smaller bill

6. An Example of Natural Selection Cont’d…
an ancestral population of finches with medium-sized bills were the first seed-eating birds to arrive on the Galapagos Islands
they typically ate medium-sized seeds
with no initial competition, the finches establish a growing population on a small island with a variety of plants, some with medium seeds but most with larger seeds

7. An Example of Natural Selection Cont’d…
the finch population grew until it reached the limit of its food supply
the birds were not all alike - some birds had slightly larger and some slightly smaller than average bills
an ancestral population of finches with medium-sized bills are the first seed-eating birds to arrive on the Galapagos Islands
they typically eat medium-sized seeds
with no initial competition, the finches establish a growing population on a small island with a variety of plants, some with medium seeds but most with larger seeds

8. An Example of Natural Selection Cont’d…
any bird with a large bill seed was able to also feed on the larger seeds
the larger-billed birds, being healthier, laid more eggs on average
their young were more likely to be born with larger bills
most of the birds must compete for the same medium-sized seeds, but any bird with an unusually large bill is able to also feed on the larger seeds
these birds have little or no competition and ample food is available to them (Darwin would say that the environment favours, or selects, these larger-billed birds)
the larger-billed birds, being healthier, lay more eggs on average
their young are more likely to be born with larger bills

9. An Example of Natural Selection Cont’d…
as this process was repeated generation after generation, the average bill size of the birds continued to increase
resulted in the large-billed ground finch found today

10. The Theory of Evolution by Natural Selection
Learning Goal: To explore Darwin’s theory of natural selection.
Success Criteria:
I know I am succeeding when I can…
explain that natural selection favours the reproductive success of individuals with certain heritable traits called adaptations
explain that process of natural selections
use natural selection to explain adaptations of species in examples
This lesson will present the many forms of evidence that convinced Darwin that species had changed over time and that species appeared to share a common ancestry. The basis of his theory on the evolution of species.

11. Homework
7.5 questions #3-5 & 7 on page 307