Evolution Flashcards
Evolution
A genetic change within a population over time
- Species accumulate difference
- Descendants differ from their ancestors
- New species arise from existing ones
Robert Hooke (1635-1703)
- Concluded fossils are remains of plants and animals
- Studied mainly “petrified wood”
- Hypothesized that living organisms had somehow turned into rock
Lamarck’s Explanation for
Evolution
- French scientist (1744-1829)
- Proposed that similar species descended from a common ancestor (fossil records)
- Hypothesized that acquired traits were passed on to offspring
Acquired Trait
- Not determined by genes
* Arises during an organism’s lifetime as a result of the organism’s experience or behavior
Thomas Malthus
- “much of human suffering – disease, famine, homelessness and war was the inescapable consequence of the human populations potential to grow much faster than the rate at which supplies of food and other resources could be produced
- Resources couldn’t keep up with the increase in population 🡪 kept the population number down
Charles Lyell (Scottish Geologist)
- Book: Principles of Geology had a strong influence on Darwin
- Proposed: gradual forces gradually change Earth’s surface and these forces are still operating today
- Natural catastrophes are very important in evolution
Darwin – a brief history
• Charles Darwin was born on February 12, 1809 in Shrewsbury, England.
• From 1831 to 1836 Darwin served as naturalist aboard the H.M.S. Beagle
on a British science expedition around the world.
• He observed many things 🡪 basis for his ideas
Darwin’s Observations
- Overproduction of Offspring – species tend to produce excessive numbers of offspring
- Heritable Variations – individuals of a population vary extensively in their characteristics and many are inherited
- Limited Natural Resources – environmental resources are limited
Alfred Wallace
- Had a theory IDENTICAL to Darwin
* Caused Darwin to publish his Origin of Species by means of natural selection
Natural Selection
Natural selection: proposed by Darwin as the mechanism of evolution
- individuals have specific inherited characteristics
- they produce more surviving offspring
- the population includes more individuals with these specific characteristics
- the population evolves and is better adapted to its present environment
Darwin’s Theories
- Descent with Modification – newer forms appearing in fossil records are actually the modified descendants of older species
- Organisms similar to each other come from a common ancestor while organisms that are more dissimilar share a remote ancestor - Modification by Natural Selection – states HOW evolution occurs
- Organisms having traits that make them better suited for survival tend to leave more offspring than organisms with fewer beneficial traits
Survival of the “Fittest”
Darwin’s theory for how long necks evolved in giraffes
Evidence for Evolution
- Homologous Structures
- Analogous Structures
- Vestigial Structures
- Embryology
- Genetics
Homologous Structures
Similar structure; different function
Analogous Structures
Similar function; different structure
Vestigial Structures
Organ has lost its’ function over time
Embryology
- The study of Embryos and their traits.
* Embryological Structure Similarities means a recent common ancestor.
Genetics
Similarities in amino acid chains.
Gene Pools
- Combined genetic information of all the members of a particular population.
- Relative Frequency of an allele - # of times the allele occurs in a gene pool compared to other alleles.
Sources of Genetic Variation
- Mutations – any change in genetic sequence
* Gene Shuffling – crossing over, which occurs during cell division (meiosis)
Allele
One or two more alternative forms of a gene that arise by mutation and are found on the same place in a chromosome.
Traits
- Single Gene Traits – traits controlled by one gene.
2. Polygenic Traits – traits controlled by two or more genes.
Natural Selection: Single Gene Trait
Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution
Natural Selection: Polygenic Traits
Natural selection can affect the distributions of phenotypes in any of three ways:
- Directional Selection
- Stabilizing Selection
- Disruptive Selection
Adaptive Radiation (Divergent Evolution)
Single species or a small group of species have evolved into several different forms that live in different ways.
Convergent Evolution
Unrelated organisms come to resemble one another
Coevolution
Two species evolve in response to changes in each other over time
Punctuated Equilibrium
Long, stable periods interrupted by brief periods of more rapid change
Mechanisms of Evolution
- Genetic Mutation
- Gene Flow
- Nonrandom Mating
- Genetic Drift
- Natural Selection
- Genetic Mutation
Polymorphism – two or more distinct phenotypes
Mutations – can be harmful or beneficial
- Gene Flow
Movement of alleles among populations by migration
- Nonrandom Mating
Individuals choose their mates
*Inbreeding – doesn’t change allele frequencies
- Genetic Drift
Changes in allele frequencies in a certain direction
Bottleneck Effect
- Example of Genetic Drift
- Severe reduction in population; reduces overall biodiversity
- Ex: Cheetahs
- Natural Selection
Formation of a new species
Speciation
- Origination of a new species.
* Species – group of organisms that breed with one another and produce fertile offspring.
What factors are involved in the
formation of a new species?
Gene pools of two populations must becomes separated for them to become new species.
Isolating Mechanisms
- As new species evolve, populations become reproductively isolated from each other.
- When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred
Behavioral Isolation
Behavioral isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior.
Geographic Isolation
Geographic isolation occurs when two populations are separated by geographic barriers such as rivers or mountains.
Temporal Isolation
Temporal isolation occurs when two or more species reproduce at different times.
Speciation of Finches
Speciation in the Galápagos finches occurred by: • Founding of a new population • Geographic isolation • Changes in new population's gene pool • Reproductive isolation • Ecological competition
- Founders Arrive:
- A few finches—species A—travel from South America to one of the Galápagos Islands.
- There, they survive and reproduce.
- Geographic Isolation
- Some birds from species A cross to a second island
* The two populations no longer share a gene pool
- Changes in the Gene Pool
- Seed sizes on the second island favor birds with large beaks
- The population on the second island evolves into population B, with larger beaks
Reproductive Isolation
- If population B birds cross back to the first island, they will not mate with birds from population A
- Populations A and B are separate species
- Organisms are unable to breed due to the isolating factors.
