7_Evolution.pdf

Chapter 7: Evolution

What is Evolution?

• Change in heritable traits over time.

• Described by Charles Darwin as "descent with modification".

Charles Darwin

• Background: English upper-middle class, average student.

• HMS Beagle: 5-year voyage to Central and South America.

• Collected diverse plant, animal, fossil, and mineral specimens.

• Interested in biodiversity, particularly the variety of finches on the Galapagos Islands.

• Noted organisms change over time and proposed natural selection as a mechanism for this change in 1859.

The Common Ancestry of Life

• All life on Earth shares a common ancestor.

• Descendants of this ancestor create Earth's biodiversity.

• Distant relationships among all life forms.

Scientific Theory of Evolution

• Evolution is an extremely well-supported scientific theory.

• Defined as a mature, coherent body of interconnected explanations based on reasoning and evidence.

• Parts of the theory may be updated or discarded based on new data.

• Unlike a hypothesis, a theory does not depend on a single test.

Evidence for Evolution

• Fossils show that organisms known today have ancestors that look different, e.g., Equus

  • Recent: Equus.

  • Late Miocene: Pliohippus.

  • Middle Miocene: Merychippus.

  • Late Eocene: Mesohippus.

Stability of Beneficial Alleles

• Some beneficial alleles are retained as organisms evolve.

• Example: FOXP2 gene.

Natural Selection and Genetic Variation

• Natural selection is driven by the existing variation within a population.

• Determines which genes persist or are eliminated.

Evolution by Natural Selection

• Process by which individuals better adapted to their environments survive and reproduce more effectively, altering the genetic makeup over time.

Four Pillars of Natural Selection

1. Variation: Individuals in a population exhibit variation in traits.

2. Inheritance: Some traits are heritable and passed on to offspring.

3. High Rate of Population Growth: More offspring are produced than can survive.

4. Differential Survival and Reproduction: Individuals with adaptive traits are more likely to survive and reproduce.

Artificial Selection

• Human-driven process where specific traits are selected to breed pairs, resulting in offspring reflecting desired phenotypes.

Sexual Selection

• Selection based on an organism's success in mating and reproduction.

• Adaptations like long tail feathers may hinder survival but can enhance mating opportunities.

A Brief History of Non-Evolutionary Thought

Catastrophism

• Belief that Earth's features are the result of catastrophic events.

• Sudden changes shape the current landscape.

Uniformitarianism

• Theory that Earth's processes are gradual and uniform over time.

• Landscapes develop through long-term gradual changes (e.g., erosion, sedimentation).

Lamarckian Evolution

• Idea that organisms change through use and disuse within their lifetimes.

• Example: Giraffe neck lengthening from stretching, which is incorrect as changes do not pass to offspring.

Modern Evolutionary Synthesis

• Period from 1930-1950 integrating Darwinian evolution with genetics.

• Acknowledged multiple mechanisms of evolution.

Mechanisms of Evolution

• Mutation: Changes in DNA introduce new alleles.

• Genetic Drift: Random changes in allele frequency, especially in small populations.

• Gene Flow: Migration resulting in genetic exchange between populations.

• Non-random Mating: Mate choice influences gene pool characteristics.

• Selection: Differential survival/reproduction of genotypes due to environmental pressures.

Hardy-Weinberg Equilibrium

• Mathematical model illustrating non-evolving populations if certain conditions are met:

  1. No differential reproductive success.

  2. Population size is large.

  3. No immigration/emigration.

  4. No new mutations.

• Evolution is inferred if any conditions are violated.

Temporal Scales in Evolution

• Distinction between microevolution (within populations) and macroevolution (interspecific variations over geological time).

Microevolution

• Evolutionary changes within populations, affecting allele frequencies over short time frames.

Macroevolution

• Major evolutionary trends and transformations studied over extended periods via fossil records and existing organisms.

Convergent Evolution

• Similar traits arise independently in different species due to similar ecological pressures, not due to close genetic relationships.

Adaptive Radiation

• Diversification where a group of organisms evolves into various forms filling different ecological niches, e.g., Galapagos finches.

Coevolution

• Interaction between two or more species leading to mutual evolutionary influence, observed in predator-prey relationships, competition, etc.

Evolution Misconceptions

• Evolution does not produce perfect organisms.

• It is not linear but instead a complex and branching process.

• Organisms do not evolve out of a need or desire.

• The phrase "survival of the fittest" is often misunderstood.

• Evolution can occur rapidly, not just over long periods.

• Evolution is observable and testable.

• Humans are subject to evolutionary processes, and evolution does not imply a continuum of organisms.

Moth Evolution Simulation

• Example: Peppered moth evolution shows differential survival based on color morphs.

• Change in allele frequency highlights microevolution and natural selection processes.

• Associated lab simulation assignment available on Canvas.

Importance of Species Conservation

• Conservation is critical for maintaining biodiversity and ecosystem stability and resilience.

• Future studies can utilize preserved species as models for understanding ecological dynamics.

Ecosystem Services

• Diverse species provide utility, nutrient cycling, and habitat regulation, contributing to overall ecological health.

• Understanding services provided helps justify conservation efforts.

Key Concepts to Remember

• Be prepared to give an example of evolution.

• Identify the main pillars of natural selection: Heritability, Variation, High rate of population growth, Variable rates of survival and reproduction.

• Recognize the forces of evolution: Selection, Mutation, Genetic Drift, Non-random Mating, Gene Flow.