Evolution and Natural Selection

How species change over time

Evolution and Natural Selection

Genetic variations are passed on through reproduction

Evidence for evolution illustrates how organisms are related

Natural selection leads to evolution

Our understanding of evolution has changed over time

Evolution

The theory that organisms today developed from more simple life forms and have changed (evolved) over time.

Natural Selection

The theory that states that those organisms best adapted to their environment have a better chance of surviving and reproducing.

EvolutionPre-Darwin Beliefs

Earth was only a few thousand years old.

We now know it is billions of years old.

Neither the planet nor the species that inhabited it had changed since the beginning of time.

We now know the planet has changed and, through fossils, discovered organisms have changed, as well.

EvolutionPre-Darwin Beliefs

Jean Pierre Lamark believed that organisms can change their traits during their lifetime by use or disuse.

He thought that these traits are passed on to offspring. Over time this would cause change in a species.

Lamark was wrong

Charles Darwin1809 - 1882

Scientist credited with the Theory of Evolution &

Natural Selection

Voyage of the HMS Beagle –

a 5 year voyage to South America and the South Pacific, collecting specimens, making observations and keeping a scientific journal of his findings.

Voyage of the BeagleWhat did Darwin find?

The finches on each island in the Galapagos had different types of beaks.

Voyage of the BeagleWhat did Darwin find?

The tortoises on each island in the Galapagos had different types of shells.

What was Darwin’s hypothesis?

Darwin hypothesized that organisms had a common ancestor, but had adapted to their particular environments and changed over time.

Darwin published his

research in 1859

Natural SelectionFor natural selection to

occur, there must be at least two varieties of a species.

For example: the peppered moth

Peppered MothsAt the beginning of the

Industrial Revolution in England, coal burning produced soot that covered the countryside in many areas

What do you think happened?

Evolution/Natural Selection

White moths became easier to see, while the black moths became harder to see. The black moths were more likely to survive and pass on the gene for dark color to their offspring.

Over time, the black moths

have become more common.

Evidence for Evolution:Common Ancestry

Common Ancestry: If species evolved from a common ancestor, then they should share common anatomical traits

Hawaiian Honeycreeper: family of

birds in Hawaii that have similar

skeletons and muscles, indicating

they are closely related. Over time, their common

ancestor evolved into several species, each

with a specialized bill for eating certain foods. Just like Darwin’s finches on the Galapagos!

Evidence for Evolution:

Homologous Structures

If animals evolved from a common ancestor, then they should share common structures – and they do!

These are called homologous

structures

Evidence for EvolutionEmbryo Development

What do you notice? List 2 observations

Evidence for Evolution:Vestigial Organs

Some organisms have structures or organs that no longer have a useful function.

These structures or organs may have been useful to the ancestors of a species, but over time have evolved into what we term vestigial organs.

Examples of Vestigial Organs

Kiwi (flightless bird)

Whales (hind leg bones)

Humans (tailbone, appendix)

Evidence for EvolutionFossils

Fossils provide a look

into the pastScientists can

trace how a species has

evolved by studying

fossils

Wrap Up the Evidence

Common AncestryHomologous StructuresVestigial OrgansEmbryonic DevelopmentFossils