Evolution�by �Natural Selection

AP Biology

AP Biology

TINTORETTO The Creation of the Animals 1550

DOCTRINE

AP Biology

But the Fossil record…

OBSERVATION

AP Biology

Life’s Natural History is a record of Successions & Extinctions

Anaerobic Bacteria

Insects

Reptiles

Dinosaurs

Mammals

Birds

Land Plants

Seed Plants

Plants

Arthropods

Chordates

Jawless Fish

Teleost Fish

Amphibians

Photosynthetic Bacteria

Green Algae

Multicellular Animals

Molluscs

1.5

4500

700

63

135

180

225

280

350

400

430

500

570

Flowering

mya

AP Biology

LaMarck

• Organisms adapted to �their environments by �acquiring traits
• change in their life time
• Disuse�organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm
• Perfection with Use & Need�the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat
• transmit acquired characteristics to next generation

AP Biology

Charles Darwin

• 1809-1882
• British naturalist
• Proposed the idea of evolution by natural selection
• Collected clear evidence to support his ideas

AP Biology

Voyage of the HMS Beagle

• Invited to travel around the world
• 1831-1836 (22 years old!)
• makes many observations of nature
• main mission of the Beagle was to chart �South American coastline

Robert Fitzroy

AP Biology

Voyage of the HMS Beagle

• Stopped in Galapagos Islands
• 500 miles off coast of Ecuador

AP Biology

Succession of types

Armadillos are native to the Americas, with most species found in South America.

Why should extinct �armadillo-like species�& living armadillos be �found on the same�continent?

AP Biology

Mylodon (left) Giant ground sloth (extinct)

“This wonderful relationship �in the same continent between �the dead and the living will…throw more light �on the appearance of organic beings on our earth,� and their disappearance from it, �than any other class of facts.”

AP Biology

Unique species

AP Biology

Darwin found… birds

Collected many different birds on the Galapagos Islands.

Finch?�

Sparrow?

Woodpecker?

Warbler?

Thought he found �very different kinds…

AP Biology

But Darwin found… a lot of finches

Darwin was amazed to �find out:

All 14 species of birds �were finches…

Finch?�

Sparrow?

Woodpecker?

Warbler?

Large Ground �Finch

Small Ground Finch

Warbler Finch

Veg. Tree Finch

​

But there is only one species of finch on the mainland!

How did�one species �of finches become�so many different�species now?

AP Biology

Tree Thinking

Large-seed eater?�

Small-seed eater?�

Warbler?

Leaf-browser?

Large Ground�Finch�

Small Ground�Finch�

Warbler Finch

Veg. Tree Finch

Ancestral�species

Descendant�species

AP Biology

Correlation of species to food source

Adaptive radiation

Seed�eaters

Flower�eaters

Insect�eaters

Rapid speciation:�new species filling new niches,�because they inherited�successful adaptations.

AP Biology

Darwin’s finches

• Differences in beaks
• associated with eating different foods
• survival & reproduction of beneficial adaptations to foods available on islands

Warbler finch

Woodpecker finch

Small insectivorous

tree finch

Large

insectivorous

tree finch

Vegetarian

tree finch

Cactus finch

Sharp-beaked finch

Small ground

finch

Medium�ground finch

Large �ground finch

Insect eaters

Bud eater

Seed eaters

Cactus

eater

Warbler

finch

Tree finches

Ground finches

AP Biology

Darwin’s finches

• Darwin’s conclusions
• small populations of original South American finches landed on islands
• variation in beaks enabled individuals to gather food successfully in the different environments
• over many generations, the populations of finches changed anatomically & behaviorally
• accumulation of advantageous traits in population
• emergence of different species

AP Biology

Seeing this gradation & �diversity of structure in �one small, intimately related group of birds, �one might really fancy that �from an original paucity of birds �in this archipelago, �one species has been taken & �modified for different ends.

AP Biology

Darwin’s finches

• Differences in beaks allowed some finches to…
• successfully compete
• successfully feed
• successfully reproduce
• pass successful traits onto their offspring

AP Biology

Correlation of species �to food source

Whoa,�Turtles, too!

More observations…

AP Biology

Many islands also show distinct local variations in tortoise morphology…

…perhaps these are �the first steps in the �splitting of one species�into several?

AP Biology

Artificial selection

This is not just a process of the past…

It is all around us today

AP Biology

Selective breeding

the raw genetic material (variation) is hidden there

AP Biology

Selective breeding

Hidden variation can be exposed through selection!

AP Biology

In historical context

• Other people’s ideas paved the path for Darwin’s thinking

competition:

struggle for survival�population growth � exceeds food supply

land masses change over �immeasurable time

AP Biology

A Reluctant Revolutionary

• Returned to England in 1836
• wrote papers describing his collections & observations
• long treatise on barnacles
• draft of his theory of �species formation in 1844
• instructed his wife to �publish this essay upon �his death
• reluctant to publish but �didn’t want ideas to die �with him

AP Biology

And then came the letter….

Then, in 1858, Darwin received a letter that changed everything…

AP Biology

The time was ripe for the idea!

AP Biology

November 24, 1859, Darwin published �

Voyage: 1831-1836

“On the Origin of Species by Means of Natural Selection”

AP Biology

Essence of Darwin’s ideas

• Natural selection
• variation exists in populations
• over-production of offspring
• more offspring than the environment can support
• competition
• for food, mates, nesting sites, escape predators
• differential survival
• successful traits = adaptations
• differential reproduction
• adaptations become more �common in population

AP Biology

LaMarckian vs. Darwinian view

• LaMarck
• in reaching higher �vegetation giraffes �stretch their necks & transmits the acquired longer neck to offspring
• Darwin
• giraffes born with longer necks survive better & leave more offspring who inherit their long necks

AP Biology

Stick your neck out…�Ask Questions!

AP Biology

Slide & Image Storage

AP Biology

AP Biology

Life has changed over time �& in turn has changed the Earth

Living creatures have�changed Earth’s environment, �making other life possible

AP Biology

Evolution as Change Over Time

Evolution!

Evolution!

Evolution!

idea accepted�before Darwin

Evolution!

AP Biology

Galapagos

Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland.

500 miles west of mainland

AP Biology

AP Biology

"Nothing in biology makes sense except in the light of evolution."

-- Theodosius Dobzhansky�March 1973

Geneticist, Columbia University

(1900-1975)

Coherent explanation of observations

AP Biology

AP Biology

Essence of Darwin’s ideas

(5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species

• Variation exists in natural populations

(2) Many more offspring are born each season than can possibly survive to maturity

(3) As a result, there is a struggle for existence

- competition

(4) Characteristics beneficial in the struggle �for existence will tend to become more common in the population, changing the average characteristics of the population

- adaptations

AP Biology

Stick your neck out…�Ask Questions!

AP Biology

The Birds…

• Galápagos birds
• 22 of the 29 species of birds on the Galapagos are endemic
• found only on these islands
• collected specimens of all
• One particular group…
• at first, he paid little attention to a series of small birds
• some were woodpecker-like, some warbler-like, & some finch-like

AP Biology

Darwin’s finches

• Darwin was amazed to find out they were all finches
• 14 species
• but only one species on South American mainland
• 500 miles away
• all the birds had to originally come �from mainland �species

Large-seed eater?�

Small-seed eater?�

Warbler?

Leaf-browser?

Finch?�

Sparrow?�

Warbler?

Wren?

How did�one species �of finches become�so many different�ones now?

AP Biology