Evolution

Evolution

Change over time Process by which modern organisms have descended from ancient organisms

Charles DarwinBorn in England 1809 Set sail on H.M.S. Beagle in

1831 for voyage around the world

Made numerous observations and collected evidence that led him to propose the theory of evolution – how life changes over time

Darwin’s Voyage

Darwin’s Observations Observed a tremendous

amount of diversity in plants and animals

68 different beetle species in one day in a Brazilian forest

Plants and animals well suited to whatever environment they inhabited

Darwin’s Observations

Intrigued by which organisms survived and produced offspring

Collected fossils that resembled organisms that were still alive

Most influenced by Galapagos Islands

Galapagos IslandsVery different

climates on each island

Paid particular attention to giant tortoises, marine iguanas, and finches

Organisms varied in predictable ways from one island to another ie. Tortoise shells

Galapagos IslandsDarwin proposed that animals

living on different islands had once been members of the same species

Species would have evolved from an original South American ancestor species after becoming isolated from one another

Galapagos Tortoises

Pinta IslandIntermediate shell

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shell

Darwin’s Influences

• Society was not receptive to Darwin’s “radical” ideas

• Certain scientists who preceded Darwin helped to shape his views

Hutton’s Theory

• Hutton’s Theory of Geological Change

• James Hutton (1795) a geologist – Rocks, mountains, and valleys are

shaped by a variety of natural forces –i.e. Rain, heat, & cold temperatures

– Geological processes operate extremely slowly therefore Earth had to be much older than a few thousand years old

Lyell’s Principles

• Lyell’s Principles of Geology

• Charles Lyell (1833) geologist–The Processes that changed Earth

in the past are the same processes that operate in the present

–Scientists recognize that Earth is many millions of years old

Movement of Earth’s Crust

Sea level

Sedimentary rocks form in horizontal layers.

When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers.

As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed.

New sediment is then deposited above the exposed older rock surface.

Sea level

Lamarck’s Theory of Evolution

• Jean Baptiste Lamarck French naturalist (1809)

• proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime.– These traits could be passed on to their

offspring.– Led to changes in species

Tendency Toward Perfection

• All organisms have a innate tendency toward perfection–Ancestors of birds acquired an urge

to fly,

–Birds kept trying to fly,

–Their wings increased in size,

–Birds are now suited to flying

Use and Disuse

• Organisms could alter the size or shape of particular organs by using their bodies in new ways–Birds try to use front limbs to fly,

they grew wings–If a winged animal did not use its

wings they would decrease in size and disappear

Inheritance of Acquired Traits

• Lamarck thought acquired characteristics could be inherited.–If you spent your life lifting

weights to build muscles then your children would inherit big muscles, too.

Crab Claws

Evaluating Lamarck

• Lamarck’s theory of evolution is incorrect because:

– He did not know how traits are inherited.

– Behavior has no effect on genetics

• He was the first:

– to develop a theory of evolution

– First to realize that groups of organisms do adapt to their environment

Population Growth

• Thomas Malthus (1798) – English Economist • Observed that babies were being born faster

than people were dying.• Malthus reasoned that if the human population

continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.– Proposed that war, famine, and disease limit

the growth of human populations.

When is a Fin a Wing?Animal Group Example Legs Fins Tail

Mammal

Bird

Fish

Amphibian

Reptile

Insect

Darwin Presents His Case

• Publication of On the Origin of Species* Darwin’s discoveries went totally

against the scientific ideas of the 1800’s

* He did not publish his research until he read Alfred Russel Wallace’s essay, which summarized Darwin’s thoughts on evolution.

* Published 25 years after his trip

Natural variation and artificial selection

• Darwin’s critics believed that all species were perfect and unchanging

• Natural variation: differences among individuals of a species, found in all types of organisms.

– Darwin proposed that much of the variation in populations can be inherited, or passed on to the next generation

Artificial Selection

• Darwin actually made some of his greatest progress studying English farmers and breeders

• Artificial selection: nature provides variation among different organisms, humans select and breed for those variations that they find useful.

Artificial Selection

Evolution by Natural Selection

* The struggle for existence* Competition for resources

* Food, water, shelter, mates, etc.

Survival of the Fittest

• The better suited an organism is to its environment, the better chance it has at surviving

• The ability of an individual to survive and reproduce in its specific environment – fitness

• The inherited characteristics that increase an organism’s chance of survival - adaptation

Descent With Modification

• Over time, natural selection has produced species that are different than their ancestors

• Looking backwards in time you should find the common ancestor of all living things – common descent

Darwin’s Tree of

Life

Tree of Life

Evidence of Evolution

Fossil Record

• Darwin believed that life on Earth has been evolving for millions of years

• Darwin saw the fossil record as a detailed record of life on Earth

Evidence of Evolution

Geographic Distribution of Living Species

• Darwin found that organisms living under similar ecological conditions end up evolving similarities without being related – Convergent Evolution

• Ex – Fish and whales

Evidence of Evolution

• Homologous Body structures

* The limbs of birds, reptiles, and mammals may have different looks but they form from the same embryonic tissue – Divergent Evolution

* Similarities of Early Development

* Animals have similar embryological development

Homologous Structures

Turtle Alligator Bird Mammals

Typical primitive fish

Embryonic Development

Summary of Darwin’s Theory

1. Variations are inherited2. In nature, tendency towards

overpopulation3. Not all organisms survive –

compete for resources4. Natural Selection – struggle

for existence

Summary of Darwin’s Theory

5. Individuals best suited to their environment survive and reproduce most successfully

6. Species change over time7. Populations today come from

modifications of species of the past8. All organisms are united into a

single tree of life by common decent