Chapter 10

EVOLUTION

ReviewEarly Ideas about Evolution Last week, we investigated some of the scientists

who had contributed to the theory of evolution

Before Charles Darwin:– Linnaeus: classification system from kingdom to

species– Lamarck: environmental change leads to use or disuse

of a structure – Other scientists:

– thought species shared ancestors rather than arising separately

– Or that more-complex forms developed from less-complex forms

Darwin’s Observations

What is Variation?Variation is the difference between physical

traits of an individual from those of other individuals in the population

What are some of the variations Darwin noticed on the Galapagos Islands?○ Neck length and leg length in tortoises, beak

thickness in finches

Darwin’s Observations What is an adaptation?

An adaptation is a feature that allows for an individual or species to better survive in their environment

What are some of the adaptations Darwin noted on the Galapagos islands?○ On islands with large hard-shelled nuts, finches had

strong thick beaks. On islands where fruits and insect were plentiful, finches had more delicate beaks.

○ On islands with tall plants, tortoises had long necks and long legs. On islands with mosses and short plants, tortoises had shorter necks and shorter legs.

Darwin’s Observations

For each finch above, think about what foods it can eat.

The tortoise to the right has long legs and a long neck.

Natural Selection

KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

Several key insights led to Darwin’s idea for natural selection.

Darwin noticed a lot of variation in domesticated plants and animals.

Artificial selection is the process by which humans select traits through breeding.

Theory of Natural Selection

Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

Heritability is the ability of a trait to be passed down.

There is a struggle for survival due to overpopulation and limited resources.

Darwin proposed that adaptations arose over many generations.

Theory of Natural Selection

Natural selection helps explain how evolution can occur

There are four main principles to the theory of natural selection1) Variation

2) Overproduction

3) Adaptation

4) Descent with modification

Theory of Natural Selection

Variation – heritable differences Overproduction – many offspring raises chances that

some will survive, but increases competition for resources

Adaptation – a certain variation may allow an individual to be more competitive

Descent with modification – Over time, natural selection will result in species with adaptations that are well suited for survival and reproduction in an environment

Fitness is the measure of survival ability and ability to produce more offspring.

Theory of Natural Selection

• Natural selection can act only on traits that already exist.

• Structures take on new functions in addition to their original function.

Interactive Review, Chapter 10, Natural Selection

Natural Selection Worksheet