Download Natural selection

 HAPPY TUESDAY 
Bellwork: Write down only the bolded red portion and your
answer.
Two species of mice live in a field in the middle of East
Texas. One mouse species is WHITE with BLACK spotting.
The other is BROWN with WHITE spotting.
After a year, the population of white mice has dramatically
decreased, while the population of the brown mice has
slightly increased.
Why would this be happening?
Standard: (7E)Analyze and
evaluate relationship of natural
selection to adaptation.
Essential Question:
What is
Evolution?
Evolution: change in heritable traits of a
population across generations (over
time).
Charles Darwin: contributed more to our understanding
of evolution than anyone else.
• Darwin traveled, made observations and collected evidence that
led him to propose his revolutionary process in a book called Origin of
the Species.
Population size is
limited by
environmental
resources
Fitness: the ability of an organism to survive and
reproduce.
•
Fitness is the result of adaptations.
Adaptation: any inherited characteristic that
increases an organism’s chance of survival.
Successful adaptations:
- enable organisms to become better suited to
their environment
- increase an individual’s ability to survive and
reproduce.
Humans have thousands of adaptations: large brain,
opposable thumbs, excellent sensory organs, light,
strong skeleton, etc.
The Primary Mechanism of
Evolution:
Natural Selection
Natural selection: the process by which individuals with
characteristics that are not well suited to their
environment either die or leave few offspring.
1. Also referred to as survival of the fittest.
2. It is not seen directly, but only observed as changes
in a population over a long time.
Summary of Darwin’s Theory:
 Individual organisms differ and some of these variations are
heritable (passed on)
 Organisms produce more offspring than can survive and
many that do survive do not reproduce
 Because more organisms are produce than can survive, they
must compete for limited resources (food, shelter, etc)
 Each unique organism has different advantages (good) and
disadvantages (bad)
 Individuals best suited to their environment survive and
reproduce successfully
 These organisms that survive pass their heritable traits to
their offspring
Summary of Darwin’s Theory cont’d:
 Other individuals that are not suited for their
environment die or leave few offspring
 This process called natural selection causes species
to change over time
 Species alive today are descended with modification
from ancestral species (their ancestors)
 This process by which diverse species evolved from
a common ancestor unites all organisms on Earth
into a single tree of life
Examples of natural selection
Bunny Simulation
If only one species is considered the "fittest", why do we still have so many
variations among species. Why do some birds have very long pointy beaks,
while other birds have short flat beaks?