H Week 16: Introduction to Evolution

Introduction to Evolution

Lecture Goals:

• Understand how variation in allele frequencies can lead to a population
• Examine how traits lead to differences in survival and fitness
• Introduce and examine the topic of evolution and common misconceptions

Click the sound button for audio!

Course Competencies: 3. Describe the principles of evolution by natural selection and their relationship to the distinguishing properties of living things. (I)

https://www.britannica.com/science/evolution-scientific-theory

Presentation Links

Artificial Selection

Evidence of Evolution

Our Understanding of Evolution

Natural Selection

EvolutionDefined

Theory of Evolution

Evolution is the gradual change in a population over time.

• Two types of evolution:
• Natural selection - environmental pressures act upon already existing alleles, which causes changes in the presence of that allele in the population
• Artificial selection - humans select traits with a specific purpose and ultimately change the species through different processes

What is Evolution?

https://en.wikipedia.org/wiki/Evidence_of_common_descent

Our Understanding of Evolution

Jean-Baptiste Lamarck

• French naturalist (1744-1829)
• Lamarckism theory
• Proposed a theory in 1809
• Said that organisms are driven by some inner force toward greater complexity

• Thought that an organism could pass on traits to their offspring that they acquired during their lives

Pre-Darwin

https://openart.ai/community/Em3Dx5YlPJ9WzwVLMmRd

• Lamarck based his theory on two observations (thought to be true in his day)
• “Use it or lose it” - individuals lose characteristics they do not require and develop those which are useful
• Inheritance of acquired traits - individuals inherit the acquired traits of their ancestors
• Examples:
• When a giraffe stretches its neck to reach leaves, this leads to offspring with longer necks
• When a blacksmith strengthens their muscles as they work, this leads to children with similar muscle development

Our Understanding of Evolution

Pre-Darwin

https://openart.ai/community/Em3Dx5YlPJ9WzwVLMmRd

Charles Darwin (1809-1882)

• Set sail on the HMS Beagle in 1831

• Became the ship’s naturalist
• Arrived in the Galapagos Islands (Ecuador) in 1835
• Observed that the animals looked similar, but also different, from island to island and from the mainland

Our Understanding of Evolution

Charles Darwin

Elliott & Fry - Swarthmore.edu (1st version); Flickr (second version), original source Corbis Images https://www.abc.net.au/listen/programs/the-history-listen/the-strange-fate-of-darwons-hms-the-beagle/10832260

• Darwin observed the animals on the Galapagos Islands

• Most obvious differences were the beak shapes and sizes of finches (small birds)
• Beak size and shape were adapted to what the finches ate

Our Understanding of Evolution

Charles Darwin

https://www.galapatours.com/destinations/darwin https://en.wikipedia.org/wiki/Evidence_of_common_descent

Our Understanding of Evolution

• Darwin studied plants, animals, and adaptations for 20 years after returning to England
• Wrote his famous book On the Origin of Species (1859)

• Described how species can change gradually over many generations and become better adapted to new environmental conditions
• Examined natural selection and artificial selection

On the Origin of Species

https://circulatingnow.nlm.nih.gov/2014/11/24/first-editions-of-darwins-origin-of-species/ https://www.britannica.com/biography/Charles-Darwin/On-the-Origin-of-Species

Discussion Post #1

• Who is Jean-Baptiste Lamarck and Charles Darwin?

• What is On the Origin of Species?
• What is evolution?

Submit for your discussion post!

Natural selection describes how environmental pressures act upon already existing alleles, which causes changes in the presence of that allele in the population.

• Has no pre-determined direction or goal
• Environmental pressures include...
• Disease
• Food availability
• Mate availability
• Climate

Natural Selection

Another word for all of the alleles present in a population is gene pool.

Environmentally Driven Evolution

"Big Male Lion" by Felinest is licensed under CC BY 2.0.

Natural Selection

Survival of the fittest

• Organisms that are better adapted to an environment are more likely to survive and reproduce than organisms that are less well adapted.
• Higher fitness = more reproduction
• Higher fitness is NOT better physical health
• Acts on already existing adaptations

Environmentally Driven Evolution

Natural Selection

Environmentally Driven Evolution

In this environment, there are tan mice and black mice. Will the tan or black mice have higher fitness?Which allele (tan or black fur color) will become more common in the population over time?

https://www.khanacademy.org/science/generations-old-and-new/x74478e8d979438e2:evolution/x74478e8d979438e2:evolution-and-natural-selection/a/hs-evolution-and-natural-selection-review

Natural Selection

Environmentally Driven Evolution

https://www.khanacademy.org/science/generations-old-and-new/x74478e8d979438e2:evolution/x74478e8d979438e2:evolution-and-natural-selection/a/hs-evolution-and-natural-selection-review

Natural Selection

Adaptations

Adaptations are any traits that an organism is born with that helps it survive and reproduce in its environment.

• Natural selection "selects" for adaptations over time
• Can be a range of characteristics

• Two types:
• Physical
• Behavioral

Can you find the animal in each photo?Click the blue eye button to see where they are.

https://www.dailymail.co.uk/news/article-8225853/Think-spot-leopard-Youve-snow-chance.html

Natural Selection

Genetic Variation

A population must have genetic variation to be able to adapt to its environment over time.

• Sources of genetic variation:
• Mutations
• Sexual reproduction
• Gene flow - movement of genes from one population to another which introduces new alleles (example: migration)

https://old-ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/52-natural-selection/species-diversification.html

Artifical Selection

Human Goal-Driven Evolution

Artifical selection describes when humans select traits with a specific purpose and ultimately change the species through different processes.

• Has a goal (unlike natural selection)
• Example:
• Domestication of dogs

"File:Louisiana Catahoula Leopard Dog - Red Leopard.jpg" by Britta Weißenborn is licensed under CC BY-SA 3.0. "Pug Dog" by alexbrn is licensed under CC BY 2.0. "Shiny Black Poodle" by Living in Monrovia is licensed under CC BY-SA 2.0.

Discussion Post #2

• Why does a population need to have genetic variation to be able to evolve?

Submit for your discussion post!

• Evidence of how life has changed over time includes...
• Fossil record
• Biogeography (study of where life is found and why)

Evidence of Evolution

Fossil Record & Biogeography

Evidence of Evolution

• Physical structures or sometimes behaviors that no longer have any purpose
• Still present in the population because they are not negatively impacting fitness

• Examples:
• Tailbones in humans

Vestigial Structures

https://flexbooks.ck12.org/cbook/ck-12-college-human-biology-flexbook-2.0/section/7.2/primary/lesson/primate-classification-and-evolution-chumbio/ https://old-ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/51-evidence-for-evolution/other-evidence.html

Evidence of Evolution

Homologous structure

• Physical structures that are physically and genetically similar between species because they share a recent common ancestor
• Example: limb bones among mammals

• Physical structures that are physically similar between species
• BUT they don't share a recent common ancestor (evolved separately)

• Example: fin in fish and flipper in dolphins

Homologous & Analogous Structures

https://sanibelseaschool.org/blog/2020/06/24/homology-and-analogy-a-lesson-in-biology/ https://kids.britannica.com/students/assembly/view/207218

Evidence of Evolution

• Recall: During DNA replication, errors sometimes occur.
• If this occurs in a gene...
• Results in a mutation
• Mutations have a wide range of severity:
• No effect
• More harmful trait (such as a genetic disorder)
• More beneficial trait

• Selection can act on the mutation that impacts survival and fitness!

Molecular Clocks

"<div class='fn'> Chromosomes and alleles</div>" by Laboratoires Servier is licensed under CC BY-SA 3.0.

• If a replication error occurs in an area of DNA that lacks a gene (non-coding DNA):
• No effect, so no natural selection happens
• Mutation remains from generation to generation
• Replication errors happen at fairly consistent and regular intervals, giving us a "clock" in DNA
• Examining the number of differences in non-gene DNA, we can get an idea of how long ago different species shared a common ancestor!

Evidence of Evolution

Molecular Clocks

"Figure 7" by plosone-phylo is licensed under CC BY 2.0. http://sgugenetics.pbworks.com/w/page/52236355/Introduction%20to%20Molecular%20Evolution%202

Evidence of Evolution

• Observing organisms with fast life cycles
• Fruit flies
• Observe how traits change over time from generation to generation
• Documenting evolutionary events
• Nitroplast
• Organelle found in some species of algae
• Can transform nitrogen gas from the atmosphere into a usable form

Direct Observation

"Figure 7" by plosone-phylo is licensed under CC BY 2.0. "Drosophila tristis" by This image is created by user Dick Belgers at waarneming.nl, a source of nature observations in the Netherlands. is licensed under CC BY 3.0.

Discussion Post #3

• Choose one piece of evidence of evolution and explain it in your own words. How does it show that evolution is occurring here on Earth?

Submit for your discussion post!

Recommended Textbook Reading

OpenStax Biology 2e: Chapter 18

Not required, but highly recommended (it can be very helpful to see the material again but phrased a little differently!)

"Figure 7" by plosone-phylo is licensed under CC BY 2.0. "Drosophila tristis" by This image is created by user Dick Belgers at waarneming.nl, a source of nature observations in the Netherlands. is licensed under CC BY 3.0.