• Identify natural selection as a mechanism for evolution.

Today’s Objective:

Can be found in the book: Pg. 393 - 399

Darwin and Natural Selection• Charles Darwin (1809- 1882)

He was an English scientist and it took him years to develop his theory of evolution.

• He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey.

• As the ship’s naturalist, Darwin studied and collected biological and fossil specimens at every port along the route.

• The specimens were quite diverse, and he became curious about possible relationships among species.

Darwin and Natural Selection

• Breeding organisms with specific traits in order to produce offspring with ideal traits is

called artificial selection.

(Intentional breeding for certain traits)

A Goldendoodle

(Golden retriever/ Poodle)

Mendel and the pea plants

Who have we studied that

bred organisms through artificial

selection?

• Darwin observed that in nature, the traits of individuals vary in populations.

• Variations are then inherited.

• Darwin hypothesized that there was a force in nature that picked which traits are better for survival in a species.

Darwin and Natural Selection

• On the Galápagos Islands, Darwin studied many species of animals and plants that are unique to the islands but similar to species elsewhere.

• These observations led Darwin to consider the possibility that species can change over time.

Darwin and Natural Selection

• He realized that individuals struggle to compete in changing environmental conditions.

• What do individuals compete for?

• Only some individuals survive the competition and live to produce offspring.

Darwin and Natural Selection

• Natural selection is the idea that organisms with favorable variations survive, reproduce, and pass their variations to the next generation.

• Organisms without these variations are less likely to survive and reproduce.

Darwin and Natural Selection

• Darwin proposed the idea of natural selection to explain how species change over time.

1.In nature, organisms produce more offspring than can survive.

Darwin and Natural Selection

2. In any population, individuals have variations.

• Fish, for example, may differ in color, size, and speed.

Darwin and Natural Selection

3. Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.

• Whereas slower individuals would not survive to reproduce.

Darwin and Natural Selection

4. Over time, offspring with FAVORABLE variations make up most of the population.

• The allele for the unfavorable variation may cease to exist.

Darwin and Natural Selection

Why do you think more and more bad bacteria (like the kind that cause sinus infections) are becoming

resistant to anti-biotics?

How do you think natural selection will affect this species

of moth? (both the same species, just

have variations)

Question 1What is the difference between artificial and natural selection?

Natural Selection:

Nature’s way of making sure the best traits live on….

“Survival of the fittest”

• Recall that an adaptation is any variation that aids an organism’s chances of survival in its environment.

• Examples are:

Thorns on plants

Special colorings for an organism

Enhanced night vision

ADAPTATIONS

• The ancestors of today’s common mole-rats looked

similar to this….

• Learning about adaptations in mole-rats can help you understand how natural selection has affected them.

ADAPTATIONS

• Some ancestral rats may have avoided predators better than others because of variations such as the

size of teeth and claws.

• Ancestral rats that survived passed their variations to offspring.

• The structural adaptations of common mole rats include large teeth and long claws.

• These body parts enable them to dig tunnels and defend against predators.

• Over time, natural selection produced modern mole-rats.

• Their blindness may have evolved because vision had no survival advantage for them.

Then Now

• Some other structural adaptations are subtle.

• Mimicry is a structural adaptation that enables one species to resemble another species.

ADAPTATIONS

• In one form of mimicry, a harmless species has adaptations that result in a physical resemblance to a harmful species.

• Another subtle adaptation is camouflage, an adaptation that enables species to blend with their surroundings.

• Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.

ADAPTATIONS