Unit 7: Theory of Evolution

The history…

• A long time ago people had no idea just how old the Earth truly is (4.6 billion years old).

• They wondered about the fossils they found of animals that no longer existed. Where had they all gone?

Charles Darwin

• was a young man, whom in 1831 was the naturalist (zoologist, botanist) on board a an English ship, the H.M.S. Beagle.

• During their five year mission who studied things that helped him develop the his theory of evolution.

The Galápagos • He visited the Galápagos

Islands and studied its plants and animals.

• These were unique to their islands but similar to species elsewhere.

• Darwin noticed that species seemed perfectly built to survive on the particular islands on which they all lived.

The Finches• Each island was home

to its own species of finch.

• Each finch had a beak that seemed just right for whatever food was available.

• What do you think that these different species each ate?

The Tortoises• The Galápagos were

named for the shells of the giant tortoises found there that resembled saddles (Galápagos).

• The tortoise above has a peaked shell and long neck, allowing to reach the high vegetation that grows on its island.

• The tortoise below has a low domed shell and feeds on grasses found on its island.

So for the next two decades…• Darwin continued

refining his ideas about evolution.

• He noticed that when he breed pigeons with desirable traits they produced offspring with those same traits.

• Breeding organisms to produce specific traits is called artificial selection.

Darwin explain natural selection

• Natural selection is a mechanism for change in populations. it occurs when organisms with favorable variations survive, reproduced and pass their variations to the next generation.

Step by step…

• Fact 1: Competition

• organisms produce more offspring than can survive.

They compete for food, water, space, mates, etc.

Fact 2

• Variation exists among individuals in any species. Some may be larger, faster, less heavy, more colorful, etc.

Fact 3• Individuals

exists with useful variations for their environment.

• They survive, reproduce and pass those variation or characteristics on to their offspring.

Fact 4

• Over time, individuals with these favorable characteristics will make up most of the population and may look totally different from their ancestors.

An example• A long time ago, in a

savanna far, far away… a species of deer existed that needed to eat. But there was not enough food to go around. Some individuals were a little taller and could reach the lower branches on trees to eat. So they did not need to eat just grass.

And so..

• More of the tall ones lived and had babies.

• And their babies looked like them.

• Every generation some babies were born that were shorter and some that were taller. The taller ones survived longer and so had more chances to reproduce. Their babies were usually taller.

And over time we got….• THE GIRAFFE!More

of the tall ones survived.

There are several forms of evidence for evolutionary theory.• fossils• anatomy• embryology• biochemistry• structural adaptations

1. Fossils• provide a record of

early life and evolutionary history.

• The further down a fossil is found the older it is.

• The record is incomplete.

• Fossils have lead us to believe that whales evolved from land-dwelling, doglike creatures.

2. Anatomy

a. homologous structures

b. analogous structures

c. vestigial structures

2a. Homologous Structures

• are structural features with a common evolutionary origin.

• The bones in the human arm are also found in cats, whales and bats.

2b. Analogous Structures

• are body parts of organisms that do not have a common evolutionary origin but are similar in function.

• The wings of birds, bats and insects all evolved independently to similar ways of life.

2c. Vestigial Structures• are body

structures in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor.

3. Embryology

• embryos are the earliest stage of growth of development of both plants and animals.

• The embryos of fish, reptiles birds and humans look surprisingly similar .

4. Biochemistry

• Nearly all organisms share DNA, ATP and many enzymes among their chemical molecules.

5. Structural Adaptations• Mimicry is a

structural adaptation that allows one species to resemble another species.

• Camouflage is an adaptation that enables species to blend with their surroundings.

Physiological adaptations can develop fast.

• Some antibiotics that were used 50 years ago are now useless against certain disease causing bacteria.

The 3 Types of Natural Selection

1. stabilizing selection

2. directional selection

3. disruptive selection

• Natural selection is survival of the fittest.

• This means those individuals that are better suited to a given environment; not necessarily the biggest or strongest individuals.

Stabilizing Selection

• is natural selection that favors average individuals in a population.

Directional Selection

• occurs when natural selection favors one of the extremes of a trait.

• This can be the smallest, longest, strongest or darkest.

Disruptive Selection

• is when individuals with either extreme of a trait’s variation are selected for

The Evolution of Species

• The evolution of a new species is called speciation.

Geographic Isolation

• occurs whenever a physical barrier divides a population.

Reproductive Isolation• occurs when

formerly interbreeding organisms can longer mate and produce fertile offspring

Polyploid

• refers to an organism with a multiple if the normal set of chromosomes.

• This can result in death or defect but can also result in new species, especially in plants.

Speciation rates

• Gradualism is the idea that species originate through a gradual change of adaptations.

• Punctuated equilibrium is the hypothesis that argues that speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between.

Patterns of Evolution• Divergent Evolution (adaptive radiation) is the

patter of evolution in which species that once were similar to an ancestral species diverge, or become different.

Patterns of Evolution• Convergent evolution

is one in which distantly related organisms evolve similar traits.

http://www.livescience.com/animals/top10_vestigial_organs-

1.html