Evolution – Just A Theory?Evolution – Just A Theory?

Evolution in the News

• 1925: Scopes “Monkey” Trial―science teacher charged with contravening

Tennessee’s Butler Act, which forbade the teaching of "any theory that denies the story of the Divine Creation of man as taught in the Bible, and to teach instead that man has descended from a lower order of animals."

• 1980s: Alabama and Louisiana laws mandating teaching of “creation science” found to be unconstitutional

• Right now: Challenges to teaching of evolutionary theory versus “Intelligent Design” in Kansas, Michigan, Pennsylvania (aclupa.blogspot.com)

Charles Darwin

• Born 1809, 5th son of wealthy physician

• Studied medicine and natural history in Edinburgh

• Studied to be a clergyman at Cambridge

• Charles Darwin – 19th century scientist

• Famous for Theory of Natural Selection―In a population, naturally occurring

variations affect which individuals survive and reproduce

―Natural selection - the force which acts on populations, and the best adapted organisms survive

―Evolution - the process by which populations change over time

Charles Darwin’s Controversial Theory

• Darwin rarely used the word “evolution” so as not to imply progress in a certain direction or towards a set goal

Charles Darwin’s Controversial Theory

150 years of controversy!150 years of controversy!

Competing Belief• Many people, even today, do not believe in the theory of evolution, but

instead, the idea of creationism.• Creationism is static and unchanging… but has meaning and purpose.

What is a Scientific Theory?

• National Academy of Science:“a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.”

• Modern science is based on the scientific method

Darwin’s theory

• Darwin published his findings from his trip around the southern hemisphere in a book called On the Origin of Species

― Darwin visited the Galapagos Islands, a group of very small islands off the coast of Ecuador.

― Even though the islands are close together, each island has a unique climate.

• Darwin proposed that evolution worked by way of natural selection.

Charles Darwin – Voyage of the Beagle

• 1831: Joined the HMS Beagle on five year voyage to South America―Studied geology, paleontology, plants and animals

Animals of the Galapagos

Darwin could tell by the shape of the GiantTortoises’ shells and their neck lengthwhich island they were from.

Darwin’s theory

1.Organisms differ, and some of this variation is heritable.

― Some cows produce more milk, some apple trees produce larger apples, etc.

― People now use artificial selection: nature provides the variation, but humans select for the variations they find useful― Ex. Only breed the dogs that lose the least amount

of fur.

Darwin’s theory

2. Organisms produce more offspring than can survive, and many that do survive do not reproduce.

3. Because more organisms are produced than can survive, they compete for limited resources.

― Struggle for existence.― In this struggle, predators that are faster get more prey.

Darwin’s theory

4. Natural selection causes species to change over time.

― Survival of the fittest!!! (natural selection)

― Adaptation is any inherited characteristic that increases an organism’s chance for survivial.

― Those individuals best adapted to their environment will survive and reproduce.

Darwin’s theory

5. Species alive today are descended with modification from ancestral species that lived in the distant past.

• All living organisms are Related to one another- common descent.• Single “tree of life” links all living things (classification)

Darwin’s Finches

• Finches looked different on different islands

• Different beak shapes depending on feeding habits

• Finches on different islands can still interbreed but geographically isolated―in the process of becoming

different species

Evolution by Natural Selection

• Natural selection - force of nature that acts on populations―Individuals that compete more effectively pass on their traits to the

next generation

• Natural variation plus natural selection = evolutionNatural variation plus natural selection = evolution

• All species could share common ancestorAll species could share common ancestor

Evidence of Evolution

1. Molecular Evidence• Study proteins (amino acid sequences)• Biologists believe that the greater the similarity between the

amino acid sequences of two organisms, the closer their relationship

2. Fossils― Fossil evidence can show us what older, possibly extinct

organisms looked like and we can compare them to organisms known today.

3. Homologous Structures― Similar bone structure can reveal evidence of evolutionary

relationships.

4. Comparative Embryology― The more similar organisms are in their embryological

development, the more closely they are related.

Molecular Evidence

•The more amino acids that arethe same, the closer the evolutionary relationshipbetween the organisms.

•Hemoglobin, protein in blood,is often looked at forcomparisons – all of these organisms have blood.

Fossils

• Radioactive dating gives relatively exact dates for fossils.

•If undisturbed, the older fossilswill be found deeper in the groundthan younger fossils.

Homologous Structures

• Homologous structures:― Structures have differentmature forms , but from thesame type of tissue.― Suggests common ancestor.

• Analogous structures:― Similar in function, butnot from the same ancestor.

Embryology

• Embryological development

• The developing embryos of many

very different organisms are

surprisingly similar in their early

stages.

Ideas that Shaped Darwin’s Theory

• At the time Darwin was doing his research, the majority of people in the world though that the earth was only a few thousand years old.

• 5 main scientists helped shape our modern theory of evolution.

Classification of Species

• Carl Linnaeus (1700s)―Identify relationships between groups of organisms ―Species: groups of organisms based on physical

resemblances and ability to interbreed―Created system of classification - taxonomy

Canidae

Canis

Canis

Vulpes

Vulpes

familiaris

lupus

vulpes

fulva

Dog

Wolf

European fox

American fox

Family Genus Species Common name

How old is the earth?

•James Hutton and Charles Lyell, both geologists, helped scientists realize that the earth is many millions of yearsold.

• Contrary to popular religious beliefs at the time.

Charles LyellJames Hutton

Lamarck – Theory of Evolution

• Jean-Baptiste Lamarck – French naturalist

• By the use or disuse of organs, organisms acquired or lost certain traits during their lifetime.

• Organisms pass on acquired characteristics to next generation

• Organisms adapt to different environments, causing branching of species― “Use it or lose it”

Lamarck – Theory of Evolution

But how are species selected in nature?

• Insight from Thomas Malthus: struggle for existence―Constant pressure of expanding population for resources

• If the population keeps growing unchecked, humans would run out of living space and food (1798).

• He felt the only thing that could limit population growth would be war, famine and disease.―Was he correct?

Darwin’s Career

• 1858: Alfred Wallace published a similar theory to Darwin’s

• 1859: Darwin published The Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life

• Darwin dubbed “most dangerous man in England” but became famous and well-respected scientist

• Later published The Descent of Man and Selection in Relation to Sex and The Expression of the Emotions in Man and Animals

Major Misconception about Evolution

Evolution has never been observed.

• Peppered moths during industrial revolution.

• Change has been directly observed.―Antibiotic Resistance―Flu Vaccines

• Creation of new species of bacteria has been directly observed.