Evolution

Darwin’s Journey and Observations

Who was Charles Darwin?

• English naturalist • Took a 5 year voyage

on the HMS Beagle • Voyage’s intent was to

explore the coast of South America

• Darwin took many specimens and made many important scientific observations

Where did the HMS Beagle go?

The Galapagos Islands

Galapagos Tortoises

• Much larger than tortoises found elsewhere • Tortoise sizes and shell shapes vary on different

islands • Islands with a lot of food à large tortoises with

dome-shaped shells • Islands with less food à smaller tortoises with

saddle-shaped shells • Why are there different shapes?

– Height, size, food, and weather!

Saddlebacked tortoise

Domed tortoise

Blue-footed BoobySea gull with bright blue feet

The foot color comes from pigments in their diet – the more well-nourished, the bluer they are.

Mating Dance

• Male parades feet in front of female, do a crazy dance, and then give the female one last look at his feet

• Females continuously evaluate male foot color in mate

• Evidence for sexual selection

Marine Iguana

• The only aquatic iguana found anywhere in the world!

• Hypothesized that the marine iguana and land iguana came from a common ancestor

What ideas influenced Darwin?

• Jean Baptiste Lamarck’s Theory of Acquired Characteristics

• Use & Disuse theory • Ex: Giraffes

– Believed that giraffes stretched necks to reach food, then passed that on to offspring

What does Lamarck’s theory mean?

• If I dye my hair red, will my babies have red hair?

• If I work out and pump iron all day, every day, will my future children be more muscular?

• If I spend hours in a tanning bed, will my children inherit darker skin?

NOPE.You can’t change your genes!

The Theory : Natural Selection

• The most fit organism survives and reproduces

• There is a struggle for existence known as competition – for food, shelter, and mates

• Living things reproduce in greater numbers than will survive

• All members of a population show variation- we are all unique!

Common Descent

• Different species share a common ancestor • If you go back far enough, all life might have a

common ancestor • Divergent evolution • What do you think the process of the creation of

new species from a common ancestor might look like?

LEOPARD MOUNTAIN LION JAGUAR HOUSECAT

CAT ANCESTOR

Steps to a new species from a common ancestor

• 1. Environmental changes • 2. Some individuals survive and some die • 3. Those that live move and inhabit a new

area • 4. Those that live become reproductively

isolated from the common ancestor • 5. New species!

What EVIDENCE do we have to support evolution?

• Fossil record – Remains of organisms – Fill in the gaps!

• Comparative anatomy – Similarities in body structure – Homology and vestigial structures

• Comparative biochemistry – DNA sequencing – Amino acid sequences

Fossils• What are fossils? • How does a jellyfish

leave a fossil? • Fossils: a remnant of

a dead organism • These can take many

forms – bones, imprints, footprints, etc.

• Paleontology – the study of fossils

Homologous Structures

• Different organisms show a unity in body plan • Inside: bone structure similar • Outside: really different uses! • Indicate common ancestry

Vestigial structures

• Remnants of an organism’s evolutionary past

• Something an ancestor would have used, but the current animal no longer needs

Do humans have tails?

Human tailbone!

Whale legs!

Snake legs!

Comparative Embryology

• Um…yikes. • Embryology – the study of the formation

and early growth of organisms. • Embryo development • Think early pregnancy / in-egg

development

Comparative Embryology

• Organisms with a common ancestor will share similar embryo development

Where’s the human?

Molecular homology

• A fancy way of saying that evolutionary relationships can be seen by looking at similarities in DNA

• All living things have a genetic code based on DNA

• DNA structure : sequences of base pairs • Closely related organisms will have

similar DNA sequences

Biogeography• Two organisms that are NOT closely related

can develop similar characteristics due to their niche

• Structures are similar, but there’s little/no evolutionary relationship

• These are called analogous structures – Example: a bird and a bat

• Both have wings for flight, but little or no evolutionary relationship

• Convergent evolution

Homology or Analogy?

Endemic Species

• Located in only one area of the world and found nowhere else!

• The Galapagos tortoises, blue footed booby, and marine iguana are all examples

• Madagascar lemur – Madagascar split from

Africa 165 million years ago!