Advanced Honors Biology

Focus on Evolution

“Nothing in biology makes sense…except in the light of evolution.”

Theodosius Dobzhansky (1973)

“Biology” during the 1800’s Late 18th-early 19th c. was an

age of discovery and natural history

Natural TheologyAll plants & animals were created “as is” ~ 6,000 to 10,000 years agoWilliam Paley---”a watch demands a watchmaker ---a design demands a designer!”

Great Geological Debate1810-1840

CatastrophismCuvier, BuffonAll changes to animals and geology are due to sudden cataclysmic events

UniformitarianismHutton & LyellThe earth was shaped by slow, gradual processes the we see today.

Born February 12, 1809 in Shrewsbury, England

EducationEntered the University of Edinburgh at age 16 to study medicineEntered Cambridge University’s Christ College in 1828 to study for the ministry

Charles Darwin (1809-1882)

Darwin’s Parents

Dr. Robert Darwin Susannah Wedgwood Darwin

Darwin’s Famous Grandfathers

Erasmus Darwin Josiah Wedgwood

Wedgwood China

J.S. Henslow (1796-1861)Darwin’s favorite

botany professorRecommends

Darwin to the British Admiralty to serve as ship’s naturalist on the H.M.S. Beagle

H.M.S. Beagle Captain Robert

FitzRoy Mission was to map

the western coast of South America for the British Navy

Darwin serves as ship’s naturalist and companion to the captain.

Voyage of H.M.S. Beagle (1831-1836)

Galapagos Islands

Galapagos Unique Animals

Return to England

Publishes what came to be known as the Voyage of the Beagle

Begins notebook on Transmutation of Species

Title page – 1905 edition

H.M.S. Beagle by Conrad Martens

Settling Down

Marries his first cousin Emma Wedgwood on January 29, 1839

Moves into an 18 acre estate in Down, England

Darwin’s Scientific Subjects

Bar

nacl

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Establishes a Theory of Atoll Formation

Keeping Quiet on Evolution Despite working on

“transmutation” since 1837 Darwin publicly says nothing.

Writes two private essays in 1842 & 1844.

Robert Chambers publishes Vestiges of the Natural History of Creation in 1844.

Contains “evolutionary ideas” but is severely ridiculed.

Alfred Russel Wallace (1823-1913)

June 18, 1858 Darwin receives a

manuscript from Wallace, a young naturalist working in the Malay Archipelago.

On the Tendency of Varieties to Depart Indefinitely from the Original Type

Joint Presentation On July 1, 1858 Charles Lyell and

Joseph Hooker present both Darwin’s 1844 and Wallace’s manuscripts before the Linnaean Society of London.

Darwin does not attend due to his son’s death from scarlet fever three days before.

Publication of The Origin Darwin finally

publishes his “big book,” On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life on November 24, 1859.

It’s 1250 copies sold out on the first day.

Darwin’s “Five Theories of Evolution”1) Evolution as Such2) Common Descent3) Variation & Natural Selection4) “Population Thinking” and

Allopatric Speciation5) Gradualness

1) Evolution as SuchChange happens!This theory was not new with Darwin.

Others like Lamarck had said that change happens over 50 years before!However, the majority of scientists in 1859 did not believe in evolutionary change.

The massive evidence that Darwin presents was so overwhelming that within a few years virtually every biologist was convinced.

What we know now…1 billion years of chemical change to form the

first cells, followed by about 3.7 billion years of biological change.

Figure 4-2

Biological Evolution

This has led to the variety of species we find on the earth today.

Figure 4-2

2) Common Descent All organisms have descended from common

ancestors by a continuous process of “branching.” Common descent explains so much about

comparative anatomy, embryology, biogeography, systematics…and behavior.

Putting humans into this branching tree of common descent takes humans away from their privileged position…and causes many people to reject the idea.

What Darwin Doesn’t DoDarwin stops short of publishing man’s place in this evolutionary tree and he never speculates on the origins of the first organisms

“I think…”Sketch from

Darwin’s 1838 notebook on transmutation

First clue that Darwin had embraced the idea of common descent

Common Descent Diagram in The Origin of Species

Tetrapod Limb Homologies

Comparative Embryology“Ontogeny recapitulates phylogeny”

3) Variation & Natural Selection

1) Individual variation in organisms within a population is the norm not the exception.

2) Populations reproduce at a geometric rate that is faster than the environment can support.

Thomas Malthus, Essay on Population 3) Some organisms will survive…most will die. 4) Which organisms will live and which will die?

Does each individual have an equal chance of survival? Darwin says---NO!Those individuals with the best adaptations will survive---Natural Selection!

Natural Selection and Adaptation: Leaving More Offspring With Beneficial Traits

Three conditions are necessary for biological evolution:

Genetic variability, Traits must be heritable, Trait must lead to differential reproduction.

An adaptive trait is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions.

Coevolution: A Biological Arms Race Interacting species can engage in a back and forth

genetic contest in which each gains a temporary genetic advantage over the other.

This often happens between predators and prey species.Or results in symbioses

Hybridization and Gene Swapping: other Ways to Exchange GenesNew species can arise through hybridization.

Occurs when individuals to two distinct species crossbreed to produce a fertile offspring.

Some species (mostly microorganisms) can exchange genes without sexual reproduction.

Horizontal gene transfer

Limits on Adaptation through Natural Selection

A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce.

Humans have a relatively slow generation time (decades) and output (# of young) versus some other species.

Darwin recognizes that it is populations that change, not individuals.

Gives rise to “population thinking”

Darwin realizes that “varieties are no more than incipient species.”

4) “Population Thinking” & Allopatric Speciation

Geographic Isolation

Darwin realizes that when a population becomes split by geographic barriers that these separate populations change in their own unique ways---Geographic Isolation.

Figure 4-10

Allopatric Speciation

After a long period of time these changes become so great that the individuals from the different populations can no longer reproduce with one another---Reproductive Isolation

5) Gradualness

GEOLOGIC PROCESSES, CLIMATE CHANGE, CATASTROPHES, AND EVOLUTION

The movement of solid (tectonic) plates making up the earth’s surface, volcanic eruptions, and earthquakes can wipe out existing species and help form new ones.

The locations of continents and oceanic basins influence climate.The movement of continents have allowed species to move.

Extinction: Lights OutExtinction occurs

when the population cannot adapt to changing environmental conditions.

The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate.

Figure 4-11

Fig. 4-12, p. 93

Tertiary

Bar width represents relative number of living speciesEra Period

Species and families experiencing

mass extinctionMillions ofyears ago

Ordovician: 50% of animal families, including many trilobites.

Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.

500

345

Cambrian

Ordovician

Silurian

Devonian

Extinction

Extinction

Pale

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cM

esoz

oic

Cen

ozoi

c

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.Carboniferous

Permian

Current extinction crisis causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Extinction

Extinction

Triassic

Jurassic

Cretaceous

250

180

65Extinction

ExtinctionQuaternary Today

Effects of Humans on Biodiversity

The scientific consensus is that human activities are decreasing the earth’s biodiversity.

Figure 4-13

Darwin’s Later Life Becomes even more

reclusive in later life. Publishes extensively,

including The Descent of Man (1871) and Expressions of the Emotions in Man and Animals (1872).

Dies of a heart attack on April 19, 1882 and is buried in Westminster Abbey near Sir Isaac Newton.

Darwin’s Legacy Darwin moved intellectual

thought from a paradigm of untestable wonder at special creation to an ability to examine the workings of the natural world, however ultimately formed, in terms of natural mechanisms and historical patterns…he in effect creates the “modern science of biology.”

Work Cited""gradualism vs. punctuated equilibrium"." 18 October 2009 <lhs2.lps.org/.../U6Evolution/gradualism.gif>.Biello, David. "Gene Swapping Helps Bacteria." Scientific American 21 November 2005."Cool Bug #9 Acacia ants." 2 October 2007. Bioblog: Music and Biology in the News . 18 October 2009

<http://bioblog.biotunes.org/bioblog/2007/10/02/cool-bug-9-acacia-ants/>."Hand in hand saving the coral reef." 13 August 2008. 18 October 2009

<coralreeftoday.com/wp-admin/acropodia/1b.jpg>.Martens, Conrad. ""HMS Beagle"." The Voyage of the Beagle by Charles Darwin. 18 October 2009 <www.sacred-

texts.com/aor/darwin/beagle/beagle.jpg>.Siegel, Robert David. ""Darwin's Finches"." 31 October 2008. Darwin Safari 2007. 18 October 2009

<http://stanford.edu/~siegelr/england/darwinsafari2007.html>.Speciation. 30 March 2009. 18 October 2009

<http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Speciation.html>.Wyhe, John van. The Complete Works of Charles Darwin online. 6 October 2009. 18 October 2009 <darwin-

online.org.uk/life14.html>.