Biol 120 - Exam 3

Why classify life

• Millions of species exist, making them difficult to study without organization.

• Classification helps scientists:

  • Identify and name organisms.

  • Understand how organisms are related and have changed over time.

  • Communicate about different species.

Taxonomic Ranks

Specific to each species but:

1. Domain

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genys

8. Species

9. Subspecies

Morphology

The physical appearance and structure of an organism.

Morphology-Based Classification

• This was how scientists in early systems used to classify life

• Grouped organisms based on their physical appearance

Why can’t you group organisms based on their physical appearance

Similar physical traits do not always mean organisms are closely related.

Convergent Evolution

• When similar traits evolve independently due to similar environments

  • This explain swhy unrelated organisms can look alike

  • Ex. Wings evolved several times in different lineages:

Phylogenic Trees

• Diagrams that show evolutionary relationships between species.

• Consist of three main parts:

  • Nodes: Common ancestors where lineages split.

  • Branches: Evolutionary lineages.

  • Tips: Species at the ends of branches.

Branching Relationships in Phylogenic Trees

• Species sharing a more recent common ancestor are more closely related

• while those sharing a more distant common ancestor are less closely related.

Ancestral vs. Derived Traits

Ancestral Traits:

• Traits believed to have been present in a common ancestor.

• Shared ancestral traits can suggest shared ancestry.

Derived Traits:

• Traits that evolved in a lineage after a common ancestor.

• Help identify branching points in phylogenetic trees.

How to Build a Phylogenetic Tree

• Start with the outgroup: The species most distantly related to the others.

• Identify the most shared trait: Look for the trait shared by the most species.

• Identify the next most shared trait: Group species based on their shared derived traits.

• Repeat: Continue until all species are placed on the tree.

Parsimony, most/least parsimous

• The approach to building a tree

• Choosing the simplest explanation that fits the observations.

• The most parsimonious tree is the one requiring the fewest evolutionary changes (gains or losses of traits).

Morphology vs DNA

Morphology:

- Classification based on what organisms look like (physical traits).

DNA:

• Classification based on genetic information.

• Compares differences in DNA base pairs (A, T, C, G).

Key Difference: Morphology and DNA can suggest the same evolutionary relationships, but sometimes they disagree.

Adding Genetic Data to Phylogenetic Trees

• Modern phylogenetic trees use DNA data alongside physical traits (morphology).

  
  

• Small differences in DNA can help distinguish species.

  
  

• Species that look similar may actually be genetically different and not closely related.

Why Do Phylogenetic Trees Disagree?

Trees based on morphology and DNA can differ because of:

• Convergent Evolution: Unrelated species independently develop similar traits.

• Gene Mutation Rates: DNA changes at different rates across lineages.

• Loss or Gain of Traits: Species can gain or lose physical traits over time.

Lamarckian evolution

Theory that traits developed during an organism's lifetime can be passed to offspring.

• Example: Giraffes stretch their necks throughout life, making them longer, and pass longer necks to their offspring.

• Made sense before scientists understood genetics.

Why it's incorrect:

• Acquired traits do not change the DNA passed to offspring.

• Example: Working out and becoming stronger doesn't mean your children will be born stronger.

Acclimation

• Happens to individuals

• Can be physiological or behavioral

• Temporary (not passed to offspring since it’s in your somatic cells, not germ cells

• Ex. Tanning in the sun

Adaption/Evolution

• Happens to populations

• Genetic change in a population over generations

• Heritable (passed through genes via your germ cells/gametes)

• Ex. skin pigmentation differences between populations living in different populations

Charles Darwin: Natural Selection (1859)

• A process where individuals with advantageous inherited traits survive and reproduce more successfully.

• Over generations, these traits become more common in the population.

• Example: Dark peppered moths becoming more common when pollution darkens trees.

  • Some moths are already genetically darker than others.

  • The environment favors dark moths.

  • Dark moths survive and reproduce more successfully.

  • Their offspring inherit the genes for darker coloration.

  • Over generations, dark moths become more common.

Artificial Selction

• Artificial selection occurs when humans act as the selective pressure by choosing which individuals reproduce, allowing them to shape a species dramatically over just a few generations.

• In artificial selection humans choose which traits to favor

  • Ex. include dog breeds developing from one ancestral species

  • Modern crops developing from wild plants

Artifical Selection vs. Natural Selection

Artificial vs. Natural Selection

Artificial Selection:

• Humans choose which traits to favor.

• Intentional and often faster.

• Goal-oriented (e.g., bigger crops).

• Example: Dog breeding.

Natural Selection:

• The environment determines which traits are advantageous.

• Unintentional and often more gradual.

• No specific goal, just survival and reproduction.

• Example: Peppered moths.

Genetic Variation: How is it generated? - Difference between the two

• Mutation: Random changes in DNA that create new alleles.

• Recombination: Shuffling of existing alleles during sexual reproduction, creating new combinations of traits.

Key Difference: Mutation creates new genetic material, while recombination rearranges existing genetic material.

How Genetics relates to evolution

• Evolution occurs at the population level, not in individuals.

• Traits must be carried in gametes (sperm or egg cells) to be passed to offspring.

Speciation

• Speciation: The formation of new species.

• Explains why phylogenetic trees have branches, as new species form from common ancestors.

• Can occur through different types of isolation

Three different types of isolation

• Geographic Isolation: Populations are physically separated by barriers (e.g., mountains, rivers).

• Behavioral Isolation: Populations have different mating behaviors, preventing them from reproducing with each other.

• Genetic Isolation: Genetic differences prevent populations from successfully reproducing or producing fertile offspring.

Reproductive Isolation

When two populations can no longer mate successfully and produce fertile offspring, potentially leading to the formation of new species.

Reproductive isolation vs genetic isolation

Reproductive isolation is the overall result, while genetic isolation is one way it can happen.

What is evolution, and how doe sit occur

• Evolution: A change in allele frequencies in a population over time.

• Occurs through four main mechanisms:

  • Mutation

  • Natural Selection

  • Gene Flow

  • Genetic Drift

Why is evolution not natural selciotn

- Natural selection is only one mechanism of evolution, not evolution itself.

Why Is Evolution NOT Survival of the Fittest?

- This describes natural selection, but it is misleading because many organisms are simply fit enough to survive and reproduce.

Why Is Evolution NOT for the Good of the Species?

- Evolution cannot predict the future or intentionally create traits that benefit a species.

Why Is Evolution NOT One-Directional?

• What is beneficial can change over time.

• A trait that is advantageous today may become harmful if environmental conditions change.

Evolution by natural selecion

1. Variation exists within a population.

2. Some of that variation is heritable (passed to offspring).

3. Individuals with certain traits survive and reproduce more successfully in a given environment.

Example: Red and Green Beetles

• Birds eat more green beetles than red beetles.

• Red beetles survive and reproduce more, becoming more common over generations.

• This is natural selection because the environment (predation) favors red beetles.

Important: Red beetles don't necessarily have a special ability to resist predators. They simply experience less predation, giving them a survival and reproductive advantage in that environment.

Gene Flow

• Gene Flow: Changes in allele frequencies due to immigration or emigration.

• Example: Brown and White Rabbits

  • If brown rabbits enter a population of white rabbits, brown-fur alleles may become more common.

  • If brown rabbits leave, brown-fur alleles may become less common.

Important: Gene flow requires alleles to enter or leave a population's gene pool, typically through successful reproduction.

Immigration

• Immigration: Individuals enter a population, bringing new alleles that can change allele frequencies.

• Remember: Immigration = Entering.

Emigration

• Emigration: Individuals leave a population, taking their alleles with them and potentially changing allele frequencies.

• Remember: Emigration = Exiting.

Genetic Drift

• Genetic Drift: Changes in allele frequencies due to random chance, not differences in fitness.

• Think of it as sampling error: A random sample of a population may have different allele frequencies than the original population.

• Causes evolution because allele frequencies change over time.

Example: Red and Green Beetles

• A random event causes more green beetles to die than red beetles.

• Red beetles become more common in the population.

• This is genetic drift, NOT natural selection, because red beetles did not have a survival advantage. The change happened purely by chance.

Four Forces of Evolution

• Mutation: Creates new alleles through random changes in DNA, generating genetic variation.

• Natural Selection: Individuals with advantageous traits survive and reproduce more successfully in a given environment.

• Gene Flow: Movement of alleles between populations through immigration and emigration, changing allele frequencies.

• Genetic Drift: Random changes in allele frequencies due to chance rather than fitness differences, especially significant in small populations.

What are Evidence Of Evolution

The fossil record, DNA Sequencing, Evolution and Society

The Fossil Record

• The totality of our knowledge of things that were alive, where, and when, from the discovery of fossils from around the world

• Helps scientists understand how life has changed over time.

DNA Sequencing

• A map of the base-pair sequence an organism has in a particular place

• Determine how genetically different two organisms are, and you can estimate how evolutionarily distant they are from each other

• More genetic differences = more distant evolutionary relationships.

Evolution and Society as Evidence of Evolution

• Evolution by natural selection has been misused to justify discrimination and oppression.

• Two major examples:

  1. Eugenics

  2. Social Darwinism

Eugenics

• Eugenics: The attempt to control human reproduction to supposedly improve the genetic quality of populations.

• Methods included forced sterilization, marriage restrictions, and segregation.

• Based on the false idea that some groups of people are biologically superior or "more evolved" than others.

• Associated with Francis Galton (Darwin's half-cousin) in the 1880s.

• Key Idea: A discriminatory misuse of ideas about heredity and artificial selection.

Social Darwinism

• Social Darwinism: The incorrect application of biological fitness to human social hierarchies.

• Believed wealth, success, and power indicated biological superiority.

• Viewed poverty, lack of education, and criminal records as signs of biological weakness.

• Used these beliefs to justify denying government assistance to disadvantaged communities.

• Key Idea: Social or economic status does not determine biological fitness.