Evolution and Natural Selection

Theories Explaining Evolution

DarwinLamarck

Organisms seem suited for their jobs and environments

• Adaptation- a characteristic that helps an organism survive.

Organisms seem suited for their jobs and environments

Identify the Adaptations!

Lamarck’s Theory Organisms acquire (develop) adaptations to

meet their needs in an environment. Specifically, an organism can change its physical traits by using its body in certain ways. The characteristics that an organism acquires during its life are then passed on to offspring.

Crab exercises his claw to make it grow larger

Crab passes on the acquired trait to offspring

Lamarck’stheory

Narrate this picture!Giraffe Evolution According to Lamarck

•

Why was Lamarck Wrong?1. Acquired traits are not inherited

(Only traits in DNA are inherited)

?

Why was Lamarck Wrong?

2. Organisms do not evolve

X

Darwins Theory: Natural Selection

Organisms born with the best adaptations survive and pass on their traits to offspring. Organisms without these adaptations die and do not reproduce. Overtime, the population changes as more organisms inherit the adaptation.

Crab is born withA slightly larger claw.

Darwin’s Theory- Natural Selection

Crab is born withA slightly larger claw.

XX

X X

Crab is born witha slightly larger claw.

Crab with largest claw survives best and reproduces most.

XX

X X

Crab is born witha slightly larger claw.

Claw helps crab survive and reproduce

XX

X X

XX XX

Crab is born witha slightly larger claw.

Claw helps crab survive and reproduce

XX

X X

Eventually, all crabs have the adaptation-the population evolved.

XX XX

One day a crab is born with an even larger claw….

One day a crab is born with an even larger claw….

…Natural selection will continue and the population evolves further

Giraffe Evolution According to Darwin

•

?

If you don’t know this word by now you NEED to!

Natural Selection- survival of the fittest

Factors that affect Natural Selection

1. 2. 3.

Factors that affect Natural Selection

1. Environmental Change

Environmental ChangeExample: A population of giraffes feeds on leaves of

small bushes on the ground and short trees. Suddenly, their environment changes! After a drought, all of the bushes on the ground die. The giraffes are left with only taller trees to eat from. Though some giraffes have necks that can reach those leaves, others do not.

Environmental Change Brainstorm: How does environmental change affect

natural selection? (Does a changing environment increase or decrease the

chance of natural selection happening? WHY?)

X

Factors that affect Natural Selection

1. Environmental Change 2. Competition

Competition Example: A population of birds uses their beaks to dig

into the soil and find worms to eat. The birds have a variety of beak sizes, but since there was always an abundant supply of worms all of the birds were able to feed. One spring the worm population decreased dramatically due to a disease and the birds had to compete over the worms. The birds with the longest beaks were able to dig deepest into the soil and find enough worms to survive.

Competition Brainstorm: How does competition affect natural

selection? (Does competition increase or decrease the chance of

natural selection happening? WHY?)

Factors that affect Natural Selection

1. Environmental Change 2. Competition3. Variation-

Factors that affect Natural Selection

1. Environmental Change 2. Competition3. Variation- differences in traits

Variation In the previous two examples, the populations of

giraffes and birds had inherent variation- the giraffes had different sized necks and the birds had different types of beaks. What would have happened if all of the giraffes had identical short necks? What would have happened if the birds all had identical small beaks? Would the populations have evolved?

VS.

Variation What would have happened if all of the giraffes had

identical short necks? What would have happened if the birds all had identical small beaks? Would the populations have evolved?

VS.

3. A student noticed that male peacocks have very beautiful and elaborate feathers while female peacocks were rather plain. He hypothesized that once all peacocks may have been rather plain but the males with the more attractive feathers were able to reproduce the most and created offspring that also had elaborate feathers. Over time, there were fewer and fewer plain males as they were more likely to die without reproducing.

Do you think the student’s theory of peacock evolution is Darwinian or Lamarckian? Explain your reasoning.

Variation Natural Selection

No Variation

VS.

Variation Natural Selection

No Variation Extinction

VS.

Partner PracticeA farmer often sprays a certain kind of insecticide, a chemical

that kills insects, on his plants to prevent locust bugs from eating all of his corn crops. One day there was a random change in the sequence of DNA in an a locust egg cell. When the egg cell hatched, the locust was resistant to the insecticide (it would not be killed by it). Since that locust could survive and reproduce, natural selection occurred until the entire population evolved to become resistant.

A) Identify the variation that existed in the insect population _____________________

B) Identify the process that created this variation _________________________

TRUE OR FALSE- Write a T next to statements that are true according to Darwin’s Theory of Natural Selection. Write an F next to statements that are false, or that describe Lamarckian evolution.

____ Evolution occurs when organisms adapt to meet their needs in an environment

____ Whole populations, not individual organisms, evolve over time based on their environment

____ Adaptations are inherited ____ Adaptations are acquired based on use ____ If an organism is not well adapted to its

environment, it dies ____ If an organism struggles in an environment it adapts