Theory of Evolution

Fossils indicate that living things have changed over time.

Several scientists had ideas to explain how.

Theory (in science)

• A model that scientists develop that can be tested with experiments

• Constantly tested against facts• Accepted theories have been tested 100s

of times by scientists all over the world.

1) Lamarck

- French scientist- Late 1700’s- early 1800’s- Developed a theory of “acquired traits”:

traits are not determined by genes but by “need”

EX: giraffe necks grow longer because they stretch to reach the leaves higher up.

2) Charles Darwin

• English scientist• Developed his theory of “natural selection”

in the mid 1800’s• Was a naturalist on the HMS Beagle• He traveled around the world, mostly the

southern hemisphere, for 5 years.

Voyage of the HMS Beagle

Darwin

Noticed organisms had some similarities even when they lived far apart.

* Darwin’s Finches

Kept records & collected specimens

Published “The Origin of Species…”

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 mainland.

• Over millions of years, the finches adapted to the foods available on each island – and evolved into separate species.

Darwin’s ideas served as a basis for theory of natural selection:

1. All organisms produce more offspring than can survive.

2. Population numbers remain fairly constant over long periods of time.

3. Organisms in a species show wide variation.

4. Some variations are inherited and passed on to the next generation.

Where does variation come fromt?

• Genes carry inheritable characteristics, also source of random variation

– crossing over• Mutations cause variation – missing letters in DNA

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.

Mutations play big role in natural selection

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 had great hearing and always head the wolves trying to sneak up on her group. She was 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.

Natural Selection

Nature selects those that are best adapted to survive.

“Survival of the Fittest”

Adaptation - any advantage (favorable trait) that an organism has

is passed to offspring.

Evolution in action:Giraffe neck length

Happy Giraffes

Hungry Giraffes

Surviving Giraffes

With Evolution You Get: Taller giraffes over time

Example of evolution through natural selection

CockroachesOver 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.)

Industrial Melanism• Peppered Moths in

Northern Europe during the Industrial Revolution– Light colored moths

blended in with the trees– Trees got darker from

soot– Light moths got eaten– Darker moths became

more common

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

• Divergent Evolution/ Adaptive radiation – many related species evolve from a single ancestral species Examples: Galapagos tortoises, finches – diverged in response to food source

• Beak differences in Hawaiian honeycreepers 

• Biodiversity is a result of the ongoing processes of evolution and extinction. Biodiversity sustains life and provides genetic raw material for adaptation to future changes in environmental conditions

Evidence of Evolution

• Fossils• Similarity of embryos• Homologous and analogous structure• Vestigial structures• Similarities in macromolecules

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

any more.

Embryoes of all vertebrates are similar – common ancestor

Homologous Structures – similar structures with similar functions.

Suggest a common ancestor.

Analogous StructuresStructures in unrelated organisms that carry out

same functions:Are the result of convergent evolution

- organisms develop similar features because of their environment; not because of common ancestry

Ex: • Kidneys in mammals and Malpighian tubules in insects• Lungs in mammals and gills in fish• Wings of insects and wings of birds• Fins in dolphins and fish

Vestigial Structures• Structures that have no function• 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 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

Similarities in Macromolecules

• All living things have the same genetic code

• The more closely 2 types of organisms are related, the more alike the arrangement of their DNA

• Proteins in horses and cows are more similar than in horses and daisies