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

Who’s the man?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’s Theory 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

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.

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 Giant Tortoises’ shells and their neck length which island they were from.

Darwin’s Theory1. 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.

Darwin’s Theory

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.

Adaptation

Preying mantis

camouflage

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 + natural Natural variation + natural

selection = evolutionselection = evolution All species could All species could

share common ancestorshare common ancestor

Evidence of Evolution1. 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 are the same, the close the

evolutionary relationship

between the organisms.

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

Fossils

• Radioactive dating gives relatively exact dates for fossils.

• If undisturbed, the older fossils will be found deeper in the ground than 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 years old.• Contrary to popular religious beliefs at the time.

Charles LyellJames Hutton

Lamarck’s 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’s Theory of Evolution

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.

Major Misconception About EvolutionEvolution 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.

Intelligent Design Defined as "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection.”

A “creator” was responsible for the design of what exists on earth

NOT a scientific theory/proposal due to the “fact” that there is a lack of evidence and should NOT be taught in science classrooms!

The Theory of Evolution The term theory in colloquial use is closer to the concept of a “hypothesis” in science (an educated guess or hunch).

In science, a theory hypothesis. A Theory is more comprehensive than a hypothesis.

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

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

Evolution in (some) schools…

Disclaimer put into biology textbooks in Georgia- this is now found to be unconstitutional!