Lecture 1 | Introduction to Evolution

Evolution (organic/biological)

The change in heritable characteristics of biological populations over successive generations

Scientific Method

Used by evolutionary biologist

• Ask a question about the world

• Formulate hypotheses

• Test hypothesis with experiments/analyses

• Draw conclusions

Proximate questions

Immediate cause of a trait and how does a trait work

ex: birds migrate due to environmental cue

Ultimate question

Asks how a trait came to be over time

• WHY did it evolve

ex: birds migrate due to increased fitness several generations ago

These are the questions of evolutionary biology

Uses for evolutionary thinking and questions

• Medicine

  • ex: development of resistance to antibiotic?

• genetics

  • ex: what genetic mechanisms cause or prevent disease?

• Sociology, psychology, anthropology

  • ex: why does every human appear unique?

How has evolutionary change driven bacterial resistance

Most people that have ever lived have died from microbial infections

• For bacterial pathogens, antibiotic resistance represents a vexing problem for medicine and is a key example of rapid evolutionary change

  • ex: MRSA

What evolutionary process is most likely responsible for the evolution of antibiotic resistance?

Natural selection

Evolutionary biology discoveries about antibiotic resistance

1. Bacterial mutants that are resistant to antibiotics occur in low frequency in most natural populations of bacteria

2. The use of antibiotics intensely selects for these resistant mutants

3. The increased usage and diversity of antibiotics is selecting for more and more multiple drug resistant bacteria

4. The evolution of the antibiotic resistance in bacteria is extremely rapid. We can observe the evolution occurring over a period of time

What does this graph show?

Shows the arms race between drug use and bacterial resistance to treat infections

• ask drugs are used, bacterial resistance identically follows afterward

Charles Darwin

Presents The Origin of Species in 1859

• started a scientific revolution

• only 150 yrs ago

  • relatively young

• industrial Revolution allowed the advancement of his ideas

Where did Darwin’s ideas come from?

Thinking was influenced by many previous naturalists

• main ideas were modifications or combinations of existing ideas

Evolutionary thought in the ancient era

While no specific mechanism has been demonstrated, evolutionary ideas have existed for 1000s of years

Essentialism

The philosophical belief that entities have a fixed essence or set characteristics hat define their fundamental nature

• proposed by Plato/Aristotle

• does not take into account imperfections/variation for the “essence”

• Variation was often ignored by biologists of the time

Scala naturae

Key idea of essentialism proposed by Aristotle

• creates a hierarchy/gradation from the inanimate to lower life forms to plants and invertebrates as a higher life form

No changes were expected in species over time

Carolus Linnaeus

Catalogues nature and established the framework of modern classification in Systema Naturae

• classified species, all intended to relate life in its closeness to “The Creator”

Uniformitarianism

Ancient geological formations can be explained by mechanisms that we can still observe today (erosion, deposition, magma flows)

• processes that cause small, gradual changes can result in massive changes over long time periods

  • fundamental to evolutionary biology

Jean-Baptiste Lamark/Lamarckian evolution

Inheritance of acquired characteristics: species vary because each has different needs and strongly exercised organs can attract more “nervous fluids”

• ex: if a giraffe needs to reach to a tree, its neck will become stretched and longer

Incorrect but was among the first to propose a mechanism to explain adaptation in nature

Darwin’s Life

Consumed interest in nature throughout his life

• took a position as naturalist on a five-year voyage on HMS Beagle

• travelled to South America and Galápagos Islands

Observations after Darwin’s voyage

Ornithologist John Gould observed that birds collected on the islands looks vaguely similar but are morphologically different

• different enough to be species

Triggered idea by Darwin that different species evolved from common ancestors

Thomas Malthus

British economist hat made the point that Human growth is faster than food production and famine will be the result

• led to Darwin’s idea of the struggle for existence: there are usually more individuals born than can survive

Main ideas that Darwin forms

1. All organisms have descended with modification from common ancestral forms of life

2. Chief agent of modification is natural selection

Alfred Russel Wallace

Described a very similar theory of natural selection to Darwin

• Spent all his time collecting specimens in Southeast Asia

Darwin gave him credit and presented at a meeting of the Royal Society in London

The Origin of Species

Based on a 500 page abstract that detailed Darwin’s ideas

5 big ideas of evolutionary theory

1. Evolution: Change over time

2. Common Descent: All life has descended

3. Gradualism: Changes have occurred incrementally

4. Population changes: Changes in the proportions of individuals with particular traits in populations

5. Natural Selection: Heritable differences impact ability to survive and reproduce

Controversy around Darwin’s Ideas

Evolution by descent with modification from common ancestors was universally accepted

• Natural selection was not

  • Mutationists held that all change over time is caused by major mutations that could form entirely new species in a single generation

  • Names “Hopeful Monsters”

Blending inheritance

Leading mechanism of inheritance in the 1800s

• Inherited material from two parents “blends together”

• Leads to the loss of variation

Particulate inheritance

A lesser known, but correct, model of inheritance

• The idea that parents pass on discrete “heritable units” (genes)’

Mendel documented this model in experiments with peas in the 1860s