Chapter 4 & 5

• Organic Evolution

Before Darwin

Jean Baptiste Lamarck

• Lamarckism: inheritance of acquired characteristics

• Transformational view of evolution

• Not supported.

1744-1829

Sir Charles Lyell

• Uniformitarianism• Laws of physics and

chemistry remain the same

• Natural processes which acted in the past will continue to act.

1797-1875

Thomas Malthus

• Concerned with human population growth

• People tended to reproduce faster than their food supply, and are forced to compete for existence.

1766-1834

Charles Darwin

• Naturalist who combined the ideas of Malthus, Lyell and others to form the theory of evolution.

1809-1882

DARWIN’S THEORY OF EVOLUTION

• A sea voyage helped Darwin frame his theory of evolution

– On his visit to the Galápagos Islands Charles Darwin observed many unique organisms

– Darwin’s main ideas can be traced back to the ancient Greeks

– Aristotle and the Judeo-Christian culture believed that species are fixed

– In the century prior to Darwin the study of fossils suggested that life forms change

– Geologists proposed that a very old Earth is changed by gradual processes

– While on the voyage of the HMS Beagle in the 1830s Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands

NorthAmerica

Europe

GreatBritain

Africa

Equator

Asia

Australia

TasmaniaNewZealand

PACIFICOCEAN

ATLANTICOCEAN

PACIFICOCEAN

PACIFICOCEAN

TheGalápagosIslands

SouthAmerica

Tierra del Fuego

Cape Horn

Cape ofGood HopeA

ndes

Pinta

MarchenaGenovesa

EquatorSantiago

Isabela

Fernandina

Florenza Española

SanCristobal

SantaCruz

SantaFe

Pinzón

DaphneIslands

40 miles

40 km0

0

– Darwin’s experiences during the voyage of the Beagle helped him frame his ideas on evolution

Evolution

Evolution

• Change over time: Organic or biological evolution is a series of changes in the

genetic composition of a population over time.

Adaptation

Adaptation

• Occurs when a heritable change in a phenotype increases an animal’s chance of successful reproduction.

Adaptation

• Occurs when a heritable change in a phenotype increases an animal’s chance of successful reproduction.

• Likely to be expressed when an organism encounters a new environment.

Adaptation

• Occurs when a heritable change in a phenotype increases an animal’s chance of successful reproduction.

• Likely to be expressed when an organism encounters a new environment.

• Not every characteristic is an adaptation to some kind of environmetal situation.

Adaptation

• Occurs when a heritable change in a phenotype increases an animal’s chance of successful reproduction.

• Likely to be expressed when an organism encounters a new environment.

• Not every characteristic is an adaptation to some kind of environmetal situation.

• A No No: evolutionary adaptations lead to perfection.

Darwinian Evolutionary Theory: The Evidence

1) Perpetual change

2) Common descent

3) Multiplication of species

4) Gradualism

5) Natural selection

I. Perpetual Change

• Darwin noticed fossils of extinct marine organisms thousands of feet above present day sea level.

The Burgess Shale

Before the Scientific Method

• People based their beliefs on their interpretations of what they saw– Without testing their ideas

• Rather, their conclusions were based on untested observations.

Snakestones!

• Some fossils you can not refute.

The Baltic amber deposits range between 35 to 40 million years old and is the largest source of amber

yet discovered.

So What do these Fossils tell us?

Geological Time

• Long before the earth’s age was known, geologists divided its history into a table of succeeding events based on the ordered layers of sedimentary rock.

– The fossil record reveals that organisms have evolved in a historical sequence

Evolutionary trends

• The fossil record allowed Darwin to view evolutionary change across the broadest scale of time.

• Animal species typically survive approximately 1 million to 10 million years, before going extinct.

I. Perpetual Change

• Darwin noticed fossils of extinct marine organisms thousands of feet above present day sea level.

• Darwin also worked on the change of animals under domestication by humans (artificial selection).

– Darwin found convincing evidence for his ideas in the results of artificial selection

• The selective breeding of domesticated animals

I. Perpetual Change

• Darwin noticed fossils of extinct marine organisms thousands of feet above present day sea level.

• Darwin also worked on the change of animals under domestication by humans (artificial selection).

• He combined these two observations to form the idea that organisms are constantly changing through time.

II. Common Descent

• Whereas Lamarck believed in multiple origins of life, Darwin believed that all life originated from a single common ancestor.

– Darwin proposed that living species are descended from earlier life forms

Thousands tomillions of years

of natural selection

Ancestral canine

African wild dog Coyote Wolf Fox Jackal

Hi There How are You!!!

6-11, p 110

• How many species of horses are there?

Grevy's Zebra (Equus grevyi) 

Burchell's Zebra (Equus burchelli) Mountain Zebra (Equus zebra)

• Asiatic Wild Asses- Kulan and Onager (Equus hemionus) - Kiang (Equus kiang)

• African Wild Asses- African Wild Ass (Equus asinus)

Przewalski's Horse (Equus caballus)

So what do these horse fossils suggest?

• Throughout the history of all forms of life, evolutionary processes generate new characteristics that are then inherited by subsequent generations.

II. Common Descent

• Whereas Lamarck believed in multiple origins of life, Darwin believed that all life originated from a single common ancestor.

• The evidence Darwin used was homology:

Homologies

• Homologies: Anatomical structures within different organisms which originated from a structure or trait of their common ancestral organism.

Vestigial Structures

What are these animals?

Analogous Structures

• The evolution of superficially similar structures in unrelated organisms is called convergent evolution.

So What?

Theory of Common Descent is Testable

• Like all good scientific theories, common descent makes several important predictions that can be tested and potentially used to reject it.

• According to this theory, we should be able to trace the genealogies of all modern species backward until they converge on ancestral lineages shared with other species, both living and extinct.