Species Change Over Time

What is evolution?• Definition:• The gradual change in a species over

time• Takes a Looooong time• Results from a change in the GENETIC

material of an organism• Not acted on at the individual level• Passed on from one generation to the

next

Early Ideas of Evolution

• Lamarck• When an individual

organism acquires a new trait IN ITS LIFETIME it passes that trait to its offspring• Ex. A giraffe wanted to reach

a higher tree so it stretched its neck. This longer neck was passed onto the next generation

• No Evidence!

What replaced Lamarcks idea?

• Charles Darwin• Developed his idea aboard the Beagle• Studied rock formations and collected

fossils• Compared animals• Galapagos Islands

• Located off the South American coast• Came up with natural selection

Galapagos Islands

South America

Darwin = populations on islands evolved from mainland species

Darwin versus Lamarck

What is natural selection?

• The process through which members of a species are best suited to their environment survive and reproduce at a higher rate than other less suited members of the species• Species adapt to their environment• Adaptation• A characteristic, a behavior, or an inherited trait

• Fitness• How well you are equipped to survive the environment you live

in

Simpler view of Natural Selection• Survival of the fittest• The most “fit” animals will be selected for and will survive.• Ex. Giraffes were all born with different heights. The ones with longer necks

were more “fit” and they were able to get additional food, survive, and pass on those traits.

Example• Depending on the food source and environment, different birds

survived and changed to best fit each island

Natural Selection• Often based on • Overproduction• Variation• Adaptation• Selection

Overproduction

• When a plant or an animal reproduces it usually creates more offspring than the environment can support• Ex. Salmon lay 100’s of eggs but

only a few will survive

Variation

• Within a species there are natural differences in traits• Occur due to mutations• Change in genetic material/DNA

• Genetic variations are passed from one generation to the next

Adaptation

• Mutation that makes an individual better able to survive• Gives organism an advantage

Selection

• Individual organisms with a particular adaptation will survive long enough to reproduce• Adaptation becomes more

common in next generation

New Species Evolve from Earlier Species

• Speciation• Evolution of a new species from

an existing species• May occur when the

environment changes dramatically or gradually• Ex. Finch (mentioned

previously); Cichlid (fish); Polar Bear

What can contribute to speciation?

• Isolation by geographical or other barriers• Species can also be isolated if they

feed on different things or reproduce at different times of year

Examples of Natural Selection:The Evolution of The Polar Bear

Our story begins with the Polar Bear’s closest living relative – the Brown Bear

The Evolution of The Polar BearAround 300,000 years ago a

small group of Brown Bears became reproductively isolated from the rest of the population

The Evolution of The Polar Bear

This small founding population of Brown Bears were able to survive and reproduce living in the Arctic Tundra. After MANY generations, a random genetic mutation occurred . . .

The Evolution of The Polar BearBecause of the genetic mutation,

a litter of Brown Bears exhibited WHITE coloration

The Evolution of The Polar Bear

How do you think the white fur color affected these bears chances of surviving long enough to have cubs of their own?

REMEMBER: Natural Selection Rests on 4 Premises:

Overproduction, Variation, Adaptation, Selection

The organism “most fit” for the environment will survive to reproduce

X

X

X

X

Not every organism will be able to reproduce. The ones most fit will

Remember traits have a genetic basis, or are inherited from parents

X

X

X

X

Advantageous traits, which allows organisms to have more offspring, will become more common

in the population over time.

X X

X

XX

XX

X

X

X

X

X

X

X

X

XX

X

X

X

X

X

X

XX

What Happened?

Through Reproductive Isolation and Natural Selection . . . One Species Evolved Into Another New Species By Adapting To Its New Environment

How long do you think this took?