Visual representation of Apple products from 1976-2007 showing form factor evolution.
Geologic Time Scale
Covers 650 million years to the present.
Illustrates the change in DNA (mutations) over time, directed by natural selection.
Changes occur over many generations.
Key Eras, Periods, and Events:
Cenozoic Era:
Quaternary Period (0-2.6 million years ago): Evolution of humans.
Neogene Period (2.6-5 million years ago): Mammals diversify.
Paleogene Period (5-50 million years ago): Extinction of dinosaurs, first primates.
Mesozoic Era:
Cretaceous Period (50-150 million years ago): First flowering plants, first birds.
Jurassic Period (150-200 million years ago): Dinosaurs diversify.
Triassic Period (200-250 million years ago): First mammals, first dinosaurs.
Paleozoic Era:
Permian Period (250-300 million years ago): Major extinctions, reptiles diversify.
Carboniferous Period (300-350 million years ago): First reptiles, scale trees, seed ferns.
Pennsylvanian.
Mississippian.
Devonian Period (350-400 million years ago): First amphibians, jawed fishes diversify, first vascular land plants.
Silurian Period (400-450 million years ago).
Ordovician Period (450-500 million years ago): First fishes.
Cambrian Period (500-550 million years ago): Sudden diversification of metazoan families, first chordates, first skeletal elements, first soft-bodied metazoans, first animal traces.
Late Proterozoic Era: (550-650 million years ago).
Lamarck vs. Darwin's Theories of Evolution
Lamarckism contrasted with Darwinism.
Lamarck’s Theory
Inheritance of acquired characteristics.
Individuals acquire traits during their lifetimes due to experience or behavior.
These traits are then passed to offspring.
Example: Giraffes evolved long necks by stretching to reach leaves, passing longer necks to offspring.
Proven wrong by Weismann in the 1870s.
Acquired traits are not genetically determined.
Darwin’s Theories
Charles Darwin
British naturalist (1809-1882).
Observed differences in species across geographic regions, particularly in the Galapagos Islands.
Darwin’s First Theory: Descent with Modification
Fossils are similar to, but different from, living organisms.
Descent with Modification:
Newer forms in the fossil record are modified descendants of older species.
This is a result of random genetic mutations.
Darwin’s Second Theory: Natural Selection
Mechanism for change in a population.
Causes evolution in nature over millions of years.
The environment selects favorable traits for success and reproduction.
Environment as a Driving Force
Environments on Earth are constantly changing:
Gradual or sudden changes in climate, human activity, natural disasters, etc.
Migration can also change the environment for an organism.
Genetic Variations
Organisms in a population have differences.
Biodiversity is crucial.
Higher genetic diversity reduces the likelihood of extinction in a changing environment.
Sources of Variation
Mutations: flawed copies of genes (related to Darwin’s Descent with Modification).
Recombination: independent assortment of genes and crossing over in meiosis.
Sexual Reproduction: Random fusion of gametes between two individuals.
Environment: plays a role; less diversity increases extinction risk.
Overproduction of Offspring
More organisms are produced than will survive.
This allows for a greater chance of survival for the species.
Struggle for Survival/Competition
Individuals compete for food, mates, and space.
Individuals with favorable variations are more successful, survive, and reproduce (survival of the fittest).
Survival and Reproduction
Favorable variations (adaptations) are passed on.
Unfavorable variations disappear.
Individuals that survive are the most fit or best suited for their environment (adapted).
Natural Selection Leads to Adaptations and Fitness
Adaptation: Result of natural selection.
Inherited variation (favorable trait) that increases a population’s chance of survival in a given environment.
Darwin’s theory is based on evidence of artificial selection.
Producing variations of the same species by selecting for desired traits in offspring.
Examples: pigeons, dogs, crops, cattle.
Population Genetics - Evolution at the Genetic Level
A group of individuals of the same species living in the same area and sharing a common gene pool.
Gene pool: The sum of all genetic information (genes) carried by members of a population.
Population Genetics
Individuals do not evolve; populations do.
Evolution is the gradual change of allele frequencies in a population (microevolution).
Gene/Allele frequency: Percentage of an allele in a gene pool.
Favorable genes become more frequent.
Example: Rock pocket mouse frequency changed from d to D with environmental change.
Hardy-Weinberg Genetic Equilibrium
Allele frequencies in a population remain the same over generations unless acted on by outside influences.
Populations do not evolve but remain constant under specific conditions.
Equilibrium Conditions
No mutations
No migration
Large population size
Random mating
No selection (natural or artificial)
Real Populations vs. Theoretical
Real populations violate conditions necessary for genetic equilibrium.
This leads to variations among organisms, natural selection, and evolution.
5 Processes of Evolution
Allele frequencies remain constant unless outside forces are at play.
These processes cause allele frequencies/evolution to occur.
1. Genetic Drift
Random change in allele frequency due to chance.
Small populations (<100) most affected.
Alleles tend to become lost or fixed.
Examples: Natural disasters, new arrivals to an isolated area.
2. Nonrandom Mating
Mate selection influenced by geographic proximity or similar characteristics.
3. Mutation
Random inheritable change in genetic material.
Can cause new alleles or forms of a trait.
Can be harmful, fatal, neutral, or beneficial in a changing environment.
4. Migration
Movement of individuals in or out of a population.
Gene flow: sharing of genes through sexual reproduction.
Consistent gene flow maintains species.
Immigration enhances variation (speciation), emigration decreases it.
Also referred to as geographic isolation.
5. Natural Selection
Most fit survive and pass down traits.
Acts on existing genetic variation.
Favorable traits are selected by environment.
Results in adapted organisms (fit).
Can lead to extinction of others (macroevolution).
Types of Selection
Stabilizing Selection
Favors average phenotypes over extremes.
Example: Medium height plants are favored because short plants can't compete for sunlight and tall plants are susceptible to wind damage.
Directional Selection
Favors phenotypes at one extreme.
Example: Giraffe necks - selection pressure against short necks resulted in a shift towards longer necks.
Disruptive Selection
Takes place when extremes of phenotypic range are selected.
Eliminates the average.
Rare.
Example: Plant pollinated by three different pollinators that prefer short, medium and tall plants. If the pollinator for medium plants disappears the population favors short and tall plants, resulting in a polymorphic population.
Evolution in Modern Times
Antibiotic resistance is an example affecting lives today.
What is this?
What has contributed to this problem?
Examples of Evolution in Action
Bacterial resistance to antibiotics
Mosquito resistance to insecticides
Peppered moth changes with the industrial revolution