Evolution. s/teachstuds/svideos.html Is evolution just a theory? Why is it so controversial?

Evolution

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

• Is evolution just a theory?

• Why is it so controversial?

• Fossils indicated that living things have changed.

• Several scientists had ideas

to explain how.

History of Evolutionary Thought

1) Lamarck (1744–1829)

• Lamarck’s Theory of Inheritance of Acquired Characteristics– Organisms could change themselves in life– Organisms gain traits they need– Pass on these changes to offspring

EX: giraffe’s necks grow longer because they stretch to reach the high

leaves.

X “Use/disuse” mechanism is wrong

Lamarck

• Think about it...

-Can you make yourself any height you want?

-If you lose an arm, will all your kids have one less arm?

-If you are born with a birthmark, will all your kids have it to?

2) Thomas Malthus (1766-1834)• Darwin was influenced by Thomas

Malthus, a political economist– Central theme of Malthus’ Essay on the

Principle of Population (1798): Populations will grow to a size that can be supported by the environment. Overpopulation leads to hunger, disease, & struggle for survival.

– Darwin proposed that in the struggle for survival, some competitors would be better equipped to survive.

3) Charles Darwin (1809-1882)• So who is Darwin??????

• English scientist

• Was a naturalist on the HMS Beagle for 5 years (traveled around the world, mostly the southern hemisphere, including the Galápagos Islands) from 1831 to 1836

• Published On the Origin of Species in 1859 introducing his theory of “natural selection” based on his observations while aboard the Beagle

Voyage of the HMS Beagle

Competition• Wallace in South America

& South East Asia

• Both naturalists came up with the idea of evolution through natural selection independently of the other– Both published their findings in 1858

• “Logically, some organisms would be able to survive better than others”– Therefore, they would pass on their traits to their

offspring

Darwin’s Finches

• Good example of how evolution occurs• Each Galapagos Island has its own unique

species of finch• Each finch had a head and body well-

adapted for life on that island• The finches were different species, but

looked similar

• Darwin realized that the finches had a common ancestor

• He proposed that originally a few seed-eating finches had flown to the islands from the mainland. Over millions of years, the finches adapted to the foods available on each island – and evolved into separate species.

In conclusion……

• NATURE had selected which finches were best fit for that type of environment.

• Finch Game

Then Darwin made 2 deductions:

1. Since most offspring don’t survive, all organisms must have to struggle for survival. (Others are eaten, or die of disease.)

2. The ones who survive and reproduce will pass on their genes.

How Does Evolution Work ??

Natural Selection

Nature selects (NATURAL SELECTION) those that are best adapted to survive.

“Survival of the Fittest”

Any adaptive advantage (a favorable trait) that an organism has

is passed to offspring.

4 Keys to Natural Selection

1. All organisms produce more offspring than can survive.

2. Some organisms in a species survive and reproduce better than others.3. Organisms in a species show wide variation.

4. Variations are inherited and passed on to the next generation.

http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html

Mutations play big a role in natural selection by creating

VARIATION.Example:

The Rabbit Tale -

Maybe once upon a

time all rabbits had short

ears and managed OK.

Then one day a mutant with big ears was born.She was always the first to dive for cover.Pretty soon, she had babies; some inherited

her big ears.They all dived for cover as fast as their mom

– faster than the short earred rabbits.Eventually, only the big earred rabbits are

left.

Example of evolution through natural selection

Cockroaches

Over the centuries, as man and cockroaches have shared homes, cockroaches have become smaller and flatter – easier access to hiding places.

(Large, fat ones more easily stomped.)

Another example - antibiotic resistance by natural selection

• Someone gets sick

• Give them antibiotics

• 99% of the bacteria are killed; only the antibiotic resistant mutants survive

• They thrive and flourish, person gets sick again

• Bacteria cannot be killed by antibiotics

Artificial Selection• Breeding for certain

traits• Environment is very easy – all organismssurvive• Breeder for (selects) the trait he or she Wants in offspring

Ex – color, size

Review

• http://youtu.be/0SCjhI86grU

Evidence of Evolution

A.Fossils

B.Similarity of embryos

C.Homologous and analogous structure

D.Vestigial structures

E.Similarities in macromolecules

• http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

A)Fossils – tell us that organisms that once lived on Earth are not

here any more.

• Fossils found closer to the surface are YOUNGER than the fossils found below

• Fossils found in the same layer, indicate that they existed at the same time

B) Embryos of all vertebrates are similar – common ancestor

C) Homologous Structures – similar structures with similar functions.

Suggest a common ancestor.

C) Analogous Structures

Structures in unrelated organisms that carry out same functions.

Exs: -Lungs in mammals

and gills in fish

-Wings of insects and

wings of birds

D) Vestigial Structures

• Reduced or nonfunctional structures• Examples: appendix, wisdom teeth, human tail

bone• Interpretation: the vestigial structure was

functional in some ancestor of the modern organism

• Snakes have pelvic bones; they are known to be the descendants of four-legged reptiles.

• Vestigial features.The skeleton of a baleen whale, a representative of the group of mammals that contains the largest living species, contains pelvic bones. These bones resemble those of other mammals, but are only weakly developed in the whale and have no apparent function.

Appendix in human

E) Similarities in Macromolecules-

Proteins • MORE differences in amino acid sequences of

distantly related species, LESS differences between species that are more closely related.

Nucleic Acids (what is a nucleic acid???)• MORE differences in DNA sequences b/t distant

relatives, LESS differences between species that are more closely related.

DNA sequencesAnimal

Human

Gorilla

Chimpanzee

Orangutan

Three pattern types of evolution

• 1) Coevolution

• 2) Convergent Evolution

• 3) Divergent Evolution

Coevolution

• When two species are in close association and evolve together. Also when a species evolves as a result of evolution in another species.

• These organisms may depend exclusively on each other & be highly specialized!

Convergent Evolution

• When un-related species becomes more similar over time.

An example is a Dolphin (mammal) and fish.

Divergent Evolution

• When related species become more different over time.

• An example is breeding dogs

Divergent evolution is the result of:

1)artificial selection

2) adaptive radiation – where many species evolve from one species

Label what type of evolution is occuring

Convergent or Divergent??

Question: Convergent or Divergent Evolution? Why?

Dolphins and Penguins

Answer: Convergent Evolution

Dolphins are mammals

Penguins are birds

Both have developed flippers to swim, stream like bodies, blubber to keep warm in water

Genetic Equilibrium

• Genetic Equilibrium is a balance of alleles within a population

****Genetic equilibrium does not exist *****

Five Reasons Why Genetic Equilibrium does not exist

1) Migration

2) Mutations

3) Genetic Drift

4) Non- Random Mating

5) Natural Selection

• 1) Migration – the movement into or out of a population

- Immigration – the movement INTO a population

- Emigration – the movement OUT a population

- The genes will move also!

2) Mutations – the alteration in alleles, or genetic information

- New traits will form, while harmful traits will eventually be eliminated

- Creates VARIATION

3) Genetic Drift - Changes in a population that are caused by change or random events.

EX: large volcano, fire, flood, diseaseMore effect on a small population more than large

population.

4) Non-random mating – leads to less “selection” and all alleles would have an equal chance of being passed on.

5) Natural Selection – where the fittest will survive. The bad traits will be eliminated from the population due to natural selection.

Tempo of Evolution

• Gradualism is a process of evolution in which the formation of new species occurs gradually

 • Punctuated Equilibrium is a process in which

the formation of new species occurs rapidly between periods of little or no change.

• Formation of new species is called Speciation

Types of Selections

Natural Selection can alter gene (trait) frequencies of a

population in three ways:

1. Stabilizing Selection

2. Directional Selection

3. Disruptive Selection

1) Stabilizing Selection• Most common form• Nature favors the average trait • Selection against the two extremes

Low Average High

Ex. Babies born with low and high birthweights have a lower chance for survivial than average

2) Directional Selection

• Nature favors one extreme

Light Medium Dark

Ex. Peppered moth-Dark Moth survived on dark sooty background.

-When pollution became lighter, nature favored light colored moth.

3) Disruptive Selection• Nature favors both extremes• Splits population into 2 groups

Small Average Large

Ex. Galapagos Finches•Small Birds, Small Seeds

•Large Birds, Large Seeds.

•Average Bird must compete with both