Honors Biology - Biological Evolution Notes

Key Terms and Concepts

  • Adaptation: A trait that enhances an organism's survival and reproduction in a particular environment.
  • Allele frequency: The relative proportion of an allele in a population.
  • Analogous structure: Structures in different species that have similar functions but evolved independently.
  • Artificial selection: The selective breeding of domesticated plants and animals by humans.
  • Behavioral isolation: Reproductive isolation based on differences in courtship or mating behaviors.
  • Biological evolution: Change in the inherited traits of a population over generations.
  • Biological fitness: The ability of an individual to survive and reproduce in its environment, contributing to the gene pool.
  • Bottleneck effect: A sharp reduction in the size of a population due to environmental events or human activities, which reduces genetic diversity.
  • Charles Darwin: Developed the theory of evolution by natural selection.
  • Fossil: Preserved remains or traces of ancient organisms.
  • Founder effect: The reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors.
  • Gene pool: The total collection of genes in a population at any one time.
  • Genetic drift: Random changes in allele frequencies in a population, especially significant in small populations.
  • Genetic equilibrium: A state of no change in allele frequencies in a population.
  • Geographic isolation: Reproductive isolation due to physical separation of populations.
  • Homologous structure: Structures in different species that have a similar underlying anatomy, indicating common ancestry.
  • Mutation: A change in the DNA sequence of an organism.
  • Natural selection: The process by which organisms better adapted to their environment tend to survive and reproduce more successfully.
  • Phylogenetic tree: A diagram that depicts the evolutionary relationships among organisms.
  • Reproductive isolation: Barriers that prevent members of different species from interbreeding and producing viable, fertile offspring.
  • Selection: The process by which certain traits become more or less common in a population due to their effects on survival and reproduction.
  • Sexual selection: A form of natural selection in which individuals with certain inherited characteristics are more likely to obtain mates.
  • Speciation: The process by which new species arise.
  • Species: A group of organisms that can interbreed and produce fertile offspring.
  • Temporal isolation: Reproductive isolation due to differences in breeding times.
  • Theory: A well-substantiated explanation of some aspect of the natural world that is based on a body of facts that have been repeatedly confirmed through observation and experimentation.
  • Vestigial structure: A structure in an organism that has lost its original function over the course of evolution.

Evolutionary Trees (Cladograms)

  • Cladistics is a method to illustrate descent from a common ancestor using cladograms.
  • Cladograms are branching diagrams showing relationships between species based on common ancestry.
  • Biologists use homologies, structural and developmental features, molecular data (DNA), and behavioral traits to reconstruct evolutionary histories.
  • Phylogenetic trees represent the most likely hypothesis based on available evidence and are revised as new data accumulates.

Cladogram Components and Analysis

  • Speciation events occur at the forks in the cladogram.
  • Derived characters are traits that differ from those seen in previous groups.

Example Cladogram Traits

  • Segmented Body
  • Legs
  • 6 Legs
  • Wings
  • Double set of wings
  • Cerci (abdominal appendages)
  • Curly Antennae

Charles Darwin and Natural Selection

  • Darwin's theory of evolution explains the adaptations of organisms and the unity and diversity of life.
  • Natural selection is a mechanism of evolution observed in species with shorter life spans.
  • Observations on the Galapagos Islands greatly contributed to Darwin's theory.
  • Adaptations enhance an organism's ability to survive and reproduce in a particular environment.
  • Natural selection, initially called “descent with modification,” is the only type of adaptive evolution observed.

Evolution Definition

  • Evolution is the change in allele frequencies in a population over time.
  • Evolution can only occur within a population; individuals do not evolve.

Darwin's Contribution

  • Darwin's observations of Galapagos finches supported the theory of natural selection.

Conditions for Natural Selection

  • Variation: Individuals in a population exhibit variation.
  • Inheritance: Traits can be passed from parents to offspring.
  • Selection: Individuals with certain traits are more likely to survive and reproduce.
  • Adaptation: The frequency of a trait that helps individuals survive or increase fitness will increase in a population.

Survival of the Fittest

  • "Survival of the fittest" is an inaccurate statement if fitness refers to strength, size, and overall health.
  • Natural selection can be described as survival of the fittest if representing an individual's contribution to the gene pool via the number of offspring it produces.
  • More offspring produced lead to more of an individual's DNA, genes, and traits in the mix, increasing the likelihood of a beneficial trait being passed on and shifting allele frequency.

Fitness

  • Fitness is an individual's contribution to the gene pool via the number of offspring it produces.
  • Survival alone does not support the evolution of a population; offspring must survive and reproduce to pass on traits.

Variation vs. Adaptation

  • Variation: Differences in traits among individuals in a population (e.g., different colors of beetles).
  • Adaptation: An inherited trait that enhances an organism's ability to survive and reproduce (e.g., camouflage coloration).

Sexual and Artificial Selection

  • Genetic variation makes evolution possible within a population.

Sexual Selection

  • Sexual selection is connected with an individual’s ability to obtain a mate.
  • Species develop physical traits, sounds, and behaviors to attract mates.
  • These traits are not always beneficial to the survival of an individual.
Traits Prominent in Males
  • Elaborate courtship rituals
  • Large in size
  • Physical strength
  • Bright coloration
  • Loud sounds
Female Selection
  • Females select traits they find desirable to pass on to their offspring.
  • Females believe these traits increase their offspring's chance of survival.
  • These traits may not help an individual survive better in its environment.
  • Sexual selection leads to a change in allele frequencies over time as traits change to meet female preferences.

Artificial Selection

  • Humans have played a role in the evolution of many organisms via artificial selection.
  • Artificial selection has led to greater yields of crops and meat.
Examples of Artificial Selection
  • All domestic dogs are descended from a common wolf ancestor; the vast amount of variation seen across the different breeds is all thanks to human preference.
  • Modern-day dogs and their wolf ancestors can vary
  • Racehorses are bred for traits like speed, strength, and endurance.
  • There are thousands of different types of apples based on traits selected by humans, including size, color, texture, and taste.
Advantages of Artificial Selection
  • Can improve nutritional value
  • Change can occur quickly
  • Increase in desirable traits
  • Can meet consumer demand
  • Increased profits
Disadvantages of Artificial Selection
  • More susceptible to environmental changes and disease
  • Can lead to inbreeding
  • Increases issues with health in organisms
  • Can be expensive

Genetic Drift

  • Natural selection, genetic drift, and gene flow can alter gene pools.
  • Genetic drift is a random event that can alter the frequency of alleles within a given population.
  • Genetic drift leads to an unstable gene pool as allele frequencies tend to fluctuate from one generation to the next.
  • Two situations in which genetic drift can have a significant impact on a population are those that produce the bottleneck effect and the founder effect.

Genetic Drift vs. Selection

  • Allele frequencies in a population change due to random chance, and it has no effect on biological fitness.
  • Genetic drift has a larger impact on smaller populations.

Mechanisms of Evolution

  • Bottleneck Effect: A natural disaster kills off a majority of a population, leaving only a few individuals with a different allele frequency than the original population.
  • Gene Flow: The transfer of genetic variation from one population to another.
  • Mutation: One of the brown beetles has a mutation (green allele) that arises spontaneously.
  • Founder Effect: Few seals colonize a new island (only orange and brown alleles exist; lost alleles). Original mainland: 14 seals, 4 colors. New island: 3 seals, 2 colors. Later: 15 seals, 2 colors.

Speciation

  • Speciation can take place with or without geographic isolation, as long as reproductive barriers evolve that keep species separate.
  • Each time speciation occurs, the diversity of life increases.
  • Reproductive isolation depends on one or more types of reproductive barriers, including isolations based on habitat, breeding times, behaviors, and physical structures.

Species Definition

  • A species is a group of organisms similar enough to interbreed and produce fertile offspring.

Speciation Definition

  • Speciation is a process where one species splits into two or more new species; it increases diversity, as allele frequencies shift.
Types of Isolation
  • Geographic: A drainage ditch forms in a field separating a large population of snails into two smaller populations; One side of the drainage ditch has been mowed and tilled for planting; The other side has been left alone and is marshy.
  • Anatomical: A species of flowering plant has experienced a speciation event that caused them to develop different flowers; The original population was pollinated by honeybees, but the new population depends on hummingbirds for pollination as the flowers are too long and narrow.
  • Behavioral: Members of the birds-of-paradise family are typically found in New Guinea and Australia; One species of bird attracts its mate with loud caws and flapping its wings back and forth, while another builds an elaborate nest to woo a female.
  • Temporal: A certain plant population only produces pollen between May and June, whereas a similar species produces pollen only during August and September; This causes them to be visited by pollinators during different parts of the year.

Scenario: Indigenous Bird Population

  • A few members of an indigenous bird population were blown to an island 500 miles off the coast of eastern Africa during a hurricane.
  • After 100 years: The island population of birds might be different from the original continental population and be considered a new species.
Habitat
  • Forested terrain with more coniferous trees and lower temperatures.
  • The island receives less rain than the mainland, which decreases the variety of plants and insects.
Adaptations
  • Thicker layer of feathers to protect from cooler temperatures.
  • Beaks slight shift in size to grasp seeds.
  • Camouflage coloration: shades of gray, brown, and black.
Variations
  • Feather layers may vary in thickness or included down feathers.
Cause of Speciation
  • Genetic drift in the form of the founder effect led to the speciation event; separated from the continental population with access to a different, smaller gene pool and a new, different environment.
  • Geographic isolation was also involved, as the two populations were separated by water and a very large distance.

Evidence for Evolution

  • Fossils of transitional forms of organisms and homologies provide strong evidence for evolution and support Darwin’s theory.

Evidence to Support Evolution

  • Fossils: The fossil record reveals the historical sequence in which organisms have evolved or gone extinct.
  • Homologous Structures: Homologies indicate patterns of descent that can be shown on evolutionary trees that reveal evolutionary relationships via common ancestors.
  • Biogeography: Species on one continent or in one region share several similar characteristics. This can be seen with organisms, with short lifespans, as they produce several generations fairly quickly. Examples include migration and continental drift/separation of Pangea.
  • Direct Observations: Ficide resistance in insects, antibiotic resistance in bacteria - were most likely analogies that arose due to convergent evolution.

Analogous vs. Homologous Structures

  • The traits that appear multiple times in different areas of the Pokemon cladogram are analogies. Justifications are that the environments likely led to the development of traits that served similar functions, even though they looked structurally different.
Examples
  • Homologous structures - each heart includes similar structures which indicate a common ancestor.
  • Analogous structures - while each limb performs a similar function, they are very different in their anatomical structure.

Convergent Evolution

  • Convergent evolution occurs when species from different evolutionary branches may come to resemble one another if they live in similar environments, and natural selection has favored similar adaptations.
  • (e.g.) A bird and an insect have no common ancestor, but they each depend on wings for movement, finding food, and evading predators.