Historic Context• Plato and Aristotle believed that

organisms were perfectly formed and adapted to the world

• Judeo Christian theology believed:– that the world is 6,000 years old– species were created

individually• Natural Theologians searched for

God’s plan through the study of nature`

• Carolus Linnaeus-

• founder of taxonomy and binomial nomenclature

– Clustered similar organisms into categories, he did not assume any evolutionary

relationship based on this classification scheme

• Paleontology developed by Cuvier

(1769-1832)

– He noticed that species appear and disappear in the fossil record

– He did not use this to support evolution, but developed catastrophism

Principles of Populations• Thomas Malthus (1798) published that

populations increase faster than environment can handle

• Capacity to over-reproduce is seen in all species

• Eventually populations stop increasing in size and reach a steady state (carrying capacity)

Geology• Hutton ( 1795) theory of gradualism that major

changes are the result of slow small changes

• Lyell (1830) geological changes throughout time have been subjected to the same forces

• Conclusions:– If geological changes are slow, earth is

older than 6,000 years old– the slow changes can build and result in

profound environmental changes over time

Relating geological evolution to biological evolution:

• Theories of biological evolution begin in the late eighteenth century

• Lamarck was the first to propose a mechanism that related environment to biological changes (1809)– Use and Disuse– Inheritance of Acquired

Characteristics

Darwin• Sails on Beagle at 22

• Noted that flora and fauna of islands off of SA were more like continental species than those of other islands with similar climate and habitats

• Contributions of Lyell and Malthus along with his observations lead him to his mechanism for evolution

Evolution

• What is evolution?• All of the accumulated changes that have

occurred over time

• Darwins definition: Descent with modification

• Life’s history is a tree with different branches• Forks of the tree represent common ancestors• Most closely related organisms share common

paths on the branching tree

• Darwin used Linnaeus’ taxonomic classification scheme to connect diversity of life

• Kingdom > phylum > class > order > family > genus > species

Mechanism : Natural Selection

• Fact 1: Over-reproduction occurs in nature • Fact 2: Populations do not increase exponentially• Fact 3: There are limited natural resources (food,

shelter)• These facts are seen in Malthus’ works on populations

• Inference 1:– struggle for survival ensues

• Fact 4: Variation exists in populations

• Fact 5: Much of the variation is heritable– Fact 4 was physically observed. Darwin’s weakness

was the 5th fact

• Inference 2:– Organisms with the best variations survive the struggle

for life

• Inference 3:– Unequal survival of organisms with different variations

leads to favorable variations accumulating over time

Key Concepts• What is the raw material necessary for the mechanism of

Natural Selection?• Heritable variations

• What is the smallest unit of evolution?• Populations

• Darwin incorporated Lyell’s gradualism into biological evolution combined with Malthus’ observations regarding populations

Examples of Natural Selection• Grants on the island of Daphne Major

observed shifts in the frequency of beak sizes over short periods of time

• Peppered moths (next page)• Antibiotic resistance in bacteria

• How do the genetic variations arise in nature?

• Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens upon which they rested.

• However, due to widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees which peppered moths rested on became blackened by soot, causing most of the light-coloured moths to die off due to predation.

• The dark-coloured moths flourished because of their ability to hide on the darkened trees

Evidence for Evolution• Artificial selection

• Island biogeography

• Fossil record

• Taxonomy

• Comparative Anatomy

• Vestigial Structures

• Comparative Embryology

• Molecular Biology

Island Biogeography

Fossil Record

Taxonomy

a)Based on physical similarities

b)Based on DNA

c)Based on fossil record

Comparative anatomy

Eye sockets in blind salamanders

Vestigial structures

Vestigial structures

Modern whales traces their ancestry to land mammals that evolved into species progressively more adapted to water.

Comparative embryology

Molecular Biology