Evolutionary Processes (L14) Flashcards
whats evolution
the process by which species change over time due to gene variation, natural selection/selection pressures and the environment
explains the origin of biodiversity
how do species change over time?
Individuals in a population have slightly different genes (genetic variation). genetic variation helps explain how organisms adapt to new changes they face
microevolution
- SMALLER changes in allele frequencies within a population
- shorter timescale (generations)
- driven by mutation, gene flow, genetic drift
- examples are: antibiotic resistance
macroevolution
LARGE-SCALE changes across species (millions of years)
- driven by mutation, gene flow, genetic drift, and speciation and extinction
What are the Four Evolutionary Forces (natures tool kit)
- Mutation
- Genetic Drift
- Gene Flow
- Natural Selection
Mutation
Random changes in DNA sequence
- new alleles which can be beneficial (increases survival), neutral or harmful (reduces survival )
Genetic Drift
- random changes in allele frequency (version of a gene) in small populations
- it can cause alleles to become more or less common by chance, not because they’re helpful or harmful.
Two types:
- Founder Effect: A small group starts a new population
- Bottleneck Effect: A large population is reduced suddenly leading to a loss of diversity
Gene Flow
The movement of genes between populations (also called migration). They introduce new alleles
- Increases genetic diversity
- Helps prevent populations from becoming genetically isolated (can stop speciation)
Natural Selection
survival of the fittest
Traits that increase fitness (survival & reproduction) become more common
Acts on existing variation; does not create new traits
Populations adapt over generations based on environmental pressures
Types of Natural Selection
Directional - favours one extreme trait version and causes the population to shift in that direction.
- In a population of birds, if bigger beaks are better at cracking hard seeds, birds with bigger beaks will survive and reproduce more.
Over time, the whole population has bigger beaks.
Stabilizing - Favors average/intermediate traits. maintains the balance
- Human babies: Very small or very large babies have more complications, while average-sized babies have higher survival.
Over time, most babies are born around an average weight
Disruptive - Favors traits that attract mates.
Sexual Selection - Favors traits that attract mates
Artificial Selection - Human-directed evolution (Dog breeds, crops like corn or broccoli)
Sources of Genetic Variation (fuel for evolution)
Mutation – Random DNA changes (typos)
Recombination – During meiosis, crossing-over creates new gene combos
Gene Flow – New alleles from migrants
Variation = raw material for evolution
Without variation, species can’t adapt.
Low variation = low adaptability → Higher risk of extinction (e.g., cheetahs)
populations with low diversity has a tough time adapting to change
Aristotle (scale of nature)
believed species were permanent and unchanging
Linnaeus (classification without evolution)
created taxonomy but didn’t believe in evolution
cuvier
found fossils of extinct organisms
Lamarck
Believed species evolve by “use and disuse” & inheritance of acquired traits (e.g. giraffes stretch necks) – incorrect but influential
darwin and wallace
independently proposed natural selection as the mechanism of evolution
What are the five key components of Darwin’s Theory of Natural Selection?
(Variations In Offspring Drive Adaptation)
Variation – Individuals differ in traits (e.g. fur color, beak size)
Inheritance – Traits are passed genetically
Overproduction – More offspring are produced than can survive
Differential survival – Individuals with favorable traits survive/reproduce more
Adaptation – Beneficial traits become more common over generations
key takeways
Evolution is not goal-directed: it’s a response to the environment.
Natural selection is not about becoming “better” or more “complex”.
Evolution produces traits that are good enough for survival in a given time/place
