1/23 Biol 114 - Week 1 Notes

Intro To Darwin and Evolution

• Pre-Darwinian Ideas:
  • Organisms produce offspring similar to themselves.
  • Artificial selection in agriculture: breeding plants and animals with beneficial traits.
  • Significant diversity exists within species.
  • Ecological factors affect individuals differently due to variations.
  • Species distribution varies based on environmental suitability.
  • Individuals typically produce more offspring than the environment can support.
• Prevailing Beliefs:
  • Special Creation: All organisms were created by a divine being approximately 6000 years ago.
  • Species are immutable and have never changed.
  • Aristotle’s Great Chain of Being: Species are organized linearly based on size and complexity, with humans at the apex.
  • Variation between individuals is considered unimportant or misleading.

Jean-Baptiste de Lamarck

• Contribution:
  • First to propose that species change over time, presenting the first formal evolutionary theory.
• Influences:
  • Based on Aristotle’s typological thinking and the idea of spontaneous generation of simple organisms.
• Theory of Acquired Characteristics:
  • Species change over time through the acquisition of traits during an individual's lifetime due to environmental pressures; these traits are then passed on to offspring.
  • Example: Giraffe's neck stretching to reach higher leaves, and this elongated neck being inherited by offspring.

Charles Darwin and the Theory of Evolution by Natural Selection

• Darwin's Contribution:
  • Charles Darwin and Russel Wallace independently developed the theory of evolution by natural selection around the same time. Darwin is more frequently credited.
• Observations from the H.M.S. Beagle Voyage (1831-1836):
  • Observed extensive variation within species, between similar species, and between distinct species.
  • Noticed that traits seemed to correlate with environmental factors such as weather, climate, and geology.
• Publication:
  • Darwin published "On the Origin of Species," presenting his conclusions.
• Darwin's Conclusions:
  • Variation combined with environmental pressure is crucial for understanding diversity and species change.
  • Key components of Darwin’s theory of evolution by natural selection:
    • All species share a common ancestor.
    • Species exhibit changes in characteristics over time.
    • Species exhibit changes in characteristics in different environments.
• Modern Theory of Natural Selection:
  • Evolution is defined as a change in genetic (allelic) frequency within a population over time.
  • Natural Selection: A mechanism through which evolution can occur.
• Requirements for Natural Selection:
  • Trait Variation:
    • Variation in a population is essential; it fuels natural selection.
    • Without variation, there are no traits to select for or against, and future generations remain the same as previous ones (except for genetic drift).
    • Almost all phenotypes exhibit variation, existing on a continuum rather than as discrete categories.
  • Heritability:
    • Traits must be heritable, meaning they are passed from parent to offspring through genes.
    • Lamarck’s ideas were flawed because acquired characteristics are generally not inherited (but note exceptions later in "Mendelian Inheritance").
  • Differential Survival:
    • Differences in survival to reproductive age must exist based on the trait.
    • Some individuals produce more breeding offspring than others.
    • Non-breeding individuals have no impact on subsequent generations.
    • Differential survival also pertains to the persistence of genes/traits across time within a genetic line in a population.
  • Differential Reproduction:
    • Due to a trait, some individuals produce more breeding offspring, passing on the genes for that trait to the next generation.
    • Greater survivorship and reproductive success of individuals with a particular trait lead to them being "naturally selected."
    • Natural selection means selected to survive in nature because of the traits they possess.
    • The relative number of breeding offspring matters: a king salmon producing 100 eggs is not as fit as one producing thousands.
• Fitness:
  • Fitness is defined as the number of viable offspring produced in an individual’s lifetime.
  • "Survival of the fittest" refers not to strength but to the number of offspring produced or the potential to produce offspring.
  • Bigger, stronger individuals often have more offspring, but this isn't always the case.
  • The term "Survival of the fittest" is often avoided by biologists due to its frequent misinterpretation by the non-scientific community.
• Adaptation:
  • Traits that are selected for by natural selection.
  • A heritable trait that increases the relative fitness of individuals.
    • Adaptation is a process where individuals within a population acquire traits that increase their relative fitness.
    • An organism can be "better adapted" to a particular environment due to the process of adaptation over a long period.
    • Adaptation as a process is similar to natural selection but implies the formation of a fitness-enhancing trait rather than just the operation of selective agents.

Artificial Selection

• Definition:
  • Analogous to natural selection, but humans are the selective agents.
• Process:
  • Humans select individuals from domesticated plants and animals to breed based on desirable traits (e.g., high food yield, ability to assist humans).
• Key Differences from Natural Selection:
  • Selective pressure results from human preference rather than non-human environmental conditions.
  • Resulting traits may not necessarily improve survival and reproduction in the wild and may not be adaptive in the wild.

Evidence for Evolution

• Three Main Conclusions of Evolutionary Theory:
  • Species are related.
  • Species (and species diversity) change over time.
  • Evolution can be observed in the short term.
• Macroevolution:
  • Large-scale changes, such as the transformation of one major taxonomic group into another (e.g., fish to amphibians to reptiles) or the creation/extinction of species.
• Microevolution:
  • Small-scale changes in a population over generations that lead to genetic divergence between populations.
  • Accumulation of microevolutionary changes over time can result in macroevolution.

Macroevolution Evidence

• Evidence for Species Relatedness:
  • Geographic proximity of similar, non-interbreeding species (e.g., different species of mockingbirds on the Galapagos Islands).
  • Homology: Similarity in traits among different species due to shared ancestry.
    • Genetic Homology: Similar gene sequences between different species.
    • Developmental Homology: Similarities in the morphology of embryos of different species.
    • Structural Homology: Similarities in the structure of body parts of different species.
• Evidence for Species Change Over Time:
  • Fossil Record:
    • Not all species existed simultaneously.
    • Extinction has occurred.
    • Transitional forms exist.
    • Major increases in species complexity take billions of years.
    • Life originated in the sea.
  • Vestigial Traits:
    • Structures commonly found in a species that have little or no function.
    • Contrast with Atavism: A vestigial trait found in very few individuals within a species.

Microevolution

• Examples:
  • Antibiotic resistance in bacteria, as seen in the sinus infection example.

Misconceptions about Evolution

• Common misunderstandings that fuel controversy:
  • Evolution implies there is no God.
  • Humans evolved from apes.
  • Individuals evolve.
  • Adaptation occurs because a species needs/wants it.
  • Evolution always leads to more complex or better organisms.
  • Animals act for the good of the species.
  • All traits are adaptive.
  • Functional traits have unlimited adaptive potential.

Evolution as a Scientific Framework

• Hypothesis Generation:
  • Evolution provides a framework for generating testable and rejectable hypotheses.
• Predictive Power:
  • Evolutionary theory allows us to make predictions about biological systems and test them through experiments.
  • Example: Homicide (Daly and Wilson 1988).

Evolutionary Trends

• Long-term trends resulting from macroevolutionary processes:
  • Increase in multicellularity.
  • Increase in complexity.
  • Increase in ways to capture energy.
  • Increase in ways to interact with the environment (biotic and abiotic).
  • Increase in diversity (snowball effect).