Charles Darwin

and His Big Idea:

Influences and

Evidence

Tuesday February 1, 2011Warmup:

Natural selection is sometimes described as “survival of the fittest”.

Lilly says that “fit” means “bigger, faster, stronger” like an Olympic athlete.

• Do you agree or disagree? Why? Give an example.

Today we will explore:• What influenced Darwin?

• What evidence did Darwin use to support his idea of evolution by natural selection?

• Born 1809 in England• Studied medicine and

theology• Joined HMS Beagle crew in

1831• Ship naturalist

– Collected specimens– Made observations– Recorded thoughts

Darwin Movie- PBS “Evolution”

• Patterns of Diversity– Plants & animals well suited to

environments– Similar ecosystems had

different animals present• Fossils – preserved

remains of ancient organisms

• Some resembled living organisms

• Some had no living counterpart

• Small group of islands west of South America

• Observed many different organisms on the islands– Tortoises– Finches

• Islands had different climates and different species

Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galapagos

What would cause such variation to occur?

Common ideas at Darwin’s time:1. Earth was only a few thousand years

old

2. Neither the Earth nor its species had changed (Earth and living things are fixed)

3. Geological features had been produced by SUDDEN catastrophic events that humans rarely witnessed

Ideas that shaped Darwin’s Thinking

• James Hutton (1795)– Geologic forces shape Earth– Layers of rock form very slowly– Estimates Earth is

millions of years old

Ideas That Shaped Darwin’s Thinking

• Thomas Malthus (1798):– Growing human population will overwhelm

resources– Darwin realized this applies even more to

plants and animals that have tons of offspring!

Ideas That Shaped Darwin’s Thinking

• Charles Lyell (1833):– Geological processes occurring now have

shaped earth’s features throughout history– Scientists must explain past events using

processes they can observe

Ideas That Shaped Darwin’s Thinking• Jean-Baptiste Lamarck (1809)

– Recognized living things have changed over time– These traits can be passed on– “inheritance of acquired characteristics”

• Organisms can alter the size/shape of their organs by using bodies in new ways

• (slight problem with this idea)

Concept Map: Evidence for Natural Selection

includes

Evidence of Evolution

Physical remains of organisms

Common ancestral species

Similar genes Similar genes

which is composed of which indicates which implies which implies

The fossil recordGeographic

distribution of living species

Homologous body structures

Similaritiesin early

development

What is Evolution?• Process by which

today’s organisms have descended from ancient organisms (ancestry)

+• Change over time

=Descent with Modification

Evidence for Evolution

How do we know evolution happens?

Fossil Record• Provides a peek at the past shows

how living things have changed over the past 3.5 billion years.

• May have bits missing, but fossil evidence clearly shows that life is old and has changed over time.

Transitional Fossils

Early whale ancestor. Land mammal, but clearly related to whales and dolphins based on specializations of ear.

Gray Whale: lives today.

The position of nostrils has changed over time.

We would expect to see fossils that show intermediate forms.

Geographic Distribution

• Some species are only found in certain parts of the world, likely because they evolved there

• Alligators in United States• Marsupials on the islands of Australia and

New Zealand

Geographic Distribution

• Organisms show more similarity to species nearby than in similar climates but far apart.

• Implies ancestry– Example: species on Galapagos Islands

share more similarities with species on mainland South America than they do with species that live on other islands with similar climates across the world

Homologous Structures

• Similar characteristics due to relatedness

QuickTime™ and a decompressor

are needed to see this picture.

Homologous Structures• The leaves look and function differently from

each other, but are all derived from a common ancestral form.

Homologous Structures• Frogs, birds, rabbits, and lizards have different

forelimbs, but they all share the same set of bones.Extinct, but shows common ancestry

Homologous Structures

Each species has a different function for their limb. Does it seem possible that they all developed the same bone structure independent of each other?

“What could be more curious…?”

http://www.pbs.org/wgbh/evolution/library/04/2/l_042_01.html

Vestigial Organs

• Traits that are not useful to an organism, but remain from a useful ancestral trait

• Ear-wiggling muscles• Tail in human and all vertebrate embryos. • Appendix • Wisdom teeth

• Hip bone of a whale

Embryology/Development

• Which of these is a pig embryo?

http://lhs2.lps.org/staff/sputnam/Biology/U6Evolution/embryology.jpe

Different vertebrates show striking similarities in early stages of development.

Embryology/Development• Snakes have legged ancestors

– Hind limb buds as embryos, but lose them before adulthood

– Fossil evidence also shows snakes with hind limbs

Cellular/ Molecular Evidence• All organisms are made of cells

– Membranes filled with water, proteins, lipids, carbohydrates, genetic material

– Most use sugar for fuel

– Produce proteins as building blocks and messengers

Molecular Evidence

• DNA: simple four-base code that provides instructions for all living things

• All life is linked to a common ancestor

• Different species share some of the same genes– Worms share 25% of their genes with

humans!

Molecular Evidence

• The more similar the DNA of two living organisms, the more closely they may be to one another– Note: many other factors play a role as

well• Activity:

– study the amino acid sequence in the hemoglobin of humans, gorillas, and horses

– use the data to show the similarities in DNA of these organisms