History of Evolutionary Thought

“This abstract, which I now publish, must necessarily be imperfect…no doubt errors have crept in, though I hope I have always been cautious in trusting to good authorities alone…A fair result can be obtained only by fully stating and balancing the facts and arguments on both sides of each question; and this cannot possibly be done here.”– Charles Darwin, On the Origin of Species, 1859.

Tree of Life

Historical Development

Before Darwin• 1600’s European anatomists began to look at

life for themselves.• Study of the intricacies of God’s design.• Guided researchers to the fundamental

question of how life works.

Rocks…again

Geologist Frame of Mind

• 1785 James Hutton proposed that the Earth must be older than a few thousand years by looking at layers formed in structures.

• Looking at life history what could you conclude about living organisms and the environment?– Life evolves as environments change

Biological Evolution

• How would you define this term?– Descent with modification.– Current species are descendants of ancestral

species that have changed over time.• We will build on this definition in the coming

days.

Historical Development

The Ecology of Human Populations• 1798 Thomas Malthus authors An Essay on the

Principle of Population as it affects the Future Improvement of Society.

• Population growth and supply.• Popularized the idea of limiting factors.

Carrying Capacity?

Historical Development

Early Concepts of Evolution• Late 1700s Jean Baptiste Lamarck coined the

idea of acquired characteristics through use and disuse.

• What is an acquired characteristic?

Lamarck

• Nature drives organisms to greater complexity over time.

• Although his ideas proven incorrect he was one of the most intelligent biologists of his time.

• Evolutionary change explains patterns in fossils and the match of organisms to their environments.

Lamarck

• Use and Disuse– Parts of the body that are used become stronger

while those that are not used deteriorate.

• Inheritance of acquired characteristics– Organisms can pass these modifications to their

offspring.

Lamarck

• Ideas make sense, let’s see if it explains what we can observe.

Early Concepts of Evolution

• You lift weights your entire life and have giant arms. Your son will have giant arms.

Early Concepts of Evolution

• You lose your arm in an accident. Due to this your child will not have an arm.

Early Concepts of Evolution

• Giraffes stretch their necks to get food. This need to stretch their neck drives evolution and the baby giraffe will have a longer neck.

Lamarck

Early Evolutionary Concepts• Tendency toward perfection and complexity.• Use and disuse.• Inheritance of acquired traits.These ideas DO NOT explain current evolutionary theory, but paved the way for its development.

The Man with the Plan

Historical Development

Natural Selection• 1859 Charles Darwin publishes On the Origin of

Species.• Found inspiration from Thomas Malthus and

Alfred Russel Wallace (you snooze, you loose).• Observable changes through selection pressure in

nature.• No mechanism for how the traits are passed from

parent to offspring.

Peas

Historical Development

The Monk and his Peas.• 1850s Gregor Mendal interbred peas and kept

track of their traits. • In certain traits he found specific ratios based

on the way he interbred the plants.• This was the first step in the discovery of

genetics.

Historical Development

Birth of Genetics• Early 1900s Thomas Hunt Morgan bred fruit

flies and studied mutations.• Mutations do not always create a new species

as had been suggested.• Source of the variation that Darwin suggested

in his original proposal!

Historical Development

Driving Forces of Natural Selection• 1920’s the scientific field of genetics became popular.

Mutations were critically analyzed.• Ronald Fisher, JBS Haldane, and Sewall Wright tested the

idea that mutations can cause small changes in the individual that can be positive or deleterious or neither in the environment.

• They were the first to create a mathematical model of evolution.

• Thinking was that small changes over time change the genetic make-up of a species.

Historical Development

The Modern Synthesis• 1930’s Theodosius Dobzhansky combined years

of genetics and population research.• Studied fruit flies and identified that all species

do not have identical genes.• Explanation for how species actually came to

existence using genetics.• Set the foundations for future studies in

evolution and building the modern synthesis.

Historical DevelopmentDNA• Scientists knew about genes but had no idea what molecule the

genetic material actually was.• Experiments verified that nucleic acids contain hereditary material.• 1953 Francis Watson and James Crick use Rosalind Franklin’s image

to create a double helix model of the structure of DNA (University of California Museum of Paleontology, 2011).

• Model opened up avenues of research including DNA replication, transcription, and translation.

• Darwin’s “variations” were identified as molecules nearly a century later.

Historical Development

Evolution and Development• 1977 Stephen Jay Gould recognized that timing of

developmental gene expression can greatly alter an organism (University of California Museum of Paleontology, 2011).

• Mutations can occur in developmental genes.• Currently scientists are studying the timing of these

developmental genes and mutations and how they influence genetic development of all body parts and may account for the variation of body plans found in nature.

Pattern of Historical Change

• Rational beings seeking the perfection of God in the natural world.

• Observations about the earth and life through anatomy.

• Forces causing the diversity of animals proposed and widely accepted later to be modified.

• Extrapolation of ideas about the human population with application to the natural world.

• Observation of the great diversity of animals and how these differences suit them in their habitats.

Pattern of Historical Change

• Experimenting with the idea of heredity to obtain measurable results.

• Observation and interdisciplinary connections to earth sciences lead to publication of On the Origin of Species.

• After publication a great curiosity with what the “variations” in natural selection were.

• Increased technology and amounts of data built upon the foundational mechanism proposed by Darwin to the theory of evolution driven by natural selection that is accepted today.