How Populations Evolve Flashcards
Theory of Evolution
- Inspired by 5 year voyage
- The idea that Earth’s species are descendants of ancestral species different than those living today
Early views on evolution
- Some early Greek philosophers suggested that life might change gradually
- Aristotle and Judeo-Christians believed that species are perfect and unchanging
Fossils
- The imprints or remains of organisms that lived in the past
- In the century prior to Darwin, fossils had been collected which suggested change over time
Lamarck’s Theory
- Jean-Baptiste Lamarck suggested that organisms evolve by the use of disuse of body parts
- Acquired characteristics are passed to offspring
Lyell’s Principles of Geology
- Inspired Darwin
- Suggested that natural forces gradually changed the earth and these changes are still happening today
Geology & Paleontology
- Darwin learned from geology that the earth was very old
- He learned from paleontology that over time, species had changed due to natural processes
On the Orgin of Species
- Darwin’s book, stated that:
- Evolution is done through natural selection
- As organisms spread, they acquire diverse adaptations specific to their environments
Artificial selection
- When humans modify a species through selection and breeding
- Also known as selective breeding
- Established by Robert Blackwell during the British Agricultural Revolution
Over Population
- A connection between natural selection and the ability to over-reproduce
Thomas Malthus
-Malthus argued that human suffering was due to the human population expanding faster than it’s resources
Darwin & Over Population
- Darwin concluded that
- Organisms vary in traits and produce more offspring than the environment can handle
- Organisms with better traits leave more offspring
- The unequal reproduction will lead to an accumulation of favorable traits
Evolution’s 5 Key Ponts
- Individuals don’t evolve, populations do
- Natural selection can increse or decrease any heritable traits
- Acquired trait’s can’t be passed on
- Evolution doesn’t lead to perfection
- Favorable traits vary with environtment changes
Darwin’s Finches
- Studied by Rosemary & Peter Grant for over 30 years in the Galapagos
- In wet years, small seeds are abundant and small beaks are favorable
- In dry years, largebeaks are favorable because small seeds are in low supply
Pesticide Resistance
- A small amount of new pesticides may kill 99% of pests, but subsequent spraying’s will be less effective
- Surviving insects have alleles to resist pesticides
- Therefore, the population gets more resistent over time
Key points of natural selection
- Natural selection is an editing process, not a march to perfection
- Natural selection is contingent on time and place, favoring those characteristics that fit the current environment
Fossil Record
-The sequence in which fossils appear within the strata of sedimentary rocks
Historical sequences
- Speicies have evolved in historical sequences
- The oldest known fossils go back 3.5 bil years ao and are prokaryotes
- The oldest eukaryotic fossils are a billion years younger
Fossil Links
- Fossils often link early, extinct species to living species
- A series of fossils traces the gradual modification of jaws and teeth in mammals
- A series of fossils shows whales coming from land mammals
Biogeography
- The geographic distribution of a species
- Suggests that organisms evolve from common ancestors
- Daein noted Galapogos animals look more like s. american animals than animals from other islands
Comparative anatomy
- The comparison of boy structures in different species
- Illustrates that evolution is a remodeling process
Homology
-The similarity in characteristics resulting from common ancestry
Homologous Structures
-Have different functions but are structurally similar due to common ancestry
Comparative Embryology
- The comparison of early stages of development in different organisms
- Reveals homologies not apparent in adults
- Ex all vertabrate embryos have a tail and throat pouches at some point
Vestigial Structures
- Remains of features that served important functions in an organism’s ancestors
- Ex/ the appendix
Advances in molecular biology
- Reveal evolutionary relationships by comparing DNA and amino acid sequences
- Indicates that
- All life forms are related and share a common DNA code for proteins
Evolutionary Tree
- Often turned sideways
- Homologous structures can be used to determine the branching sequence
- Include anatomical and molecular structures
Population
- A group of individuals of the same species living in the same place at the same time
- May be isolated, which leads to interbreed
Gene pool
-The total collection of genes in a population at any time
Microevolution
-A change in the relative frequencies of alleles in a gene pool over time
Population Genetics
-Shows how populations change genetically over time
Modern synthesis
Connects Darwin’s theory with population genetics
Mutation
- Change the nucleotide sequence of DNA
- The ultimate source of new alleles
Chromosomal Duplication
- Is an important source of genetic variation
- If a gene is duplicated, the new copy can undergo mutation without it affecting the original copy
Sexual reproduction
Shuffles alleles to produce new combos in 3 ways:
- Homologous chromosomes sort independently as they separate during anaphase I of meiosis
- During prophase I of meiosis, homologous chromosomes cross over and exchange genes
- A further variation occurs when a sperm unites with the egg
Shuffled alleles
-The frequency of alleles and genotypes do not change
Hardy- Weinberg
-Allele frequency will remain in equilibrium until outside forces act to change the frequency
5 Hardy- Weinberg Conditions
- A large population
- No gene flow between populations
- No mutations
- Random mating
- No natural selection
Hardy-Weinberg equation
- P^2 + 2pq +q^2=100
- Homozygous + heterozygous + homozygous recessive
Hardy-Weinberg Disruption
- Small population
- Individuals moving in and out of a population
- Mutations can change or delete alleles
- Preferential mating
- Unequal survival and reproductive success (natural selection)
Causes of Evolutionary Change
- Natural selection
- Genetic drift
- Gene flow
Natural selection
-If individuals differ in their survival and reproductive success, natural selection will alter allele frequencies
Genetic drift
-Change in the gene pool due to chance
Bottleneck Effect
-Leads to a loss of genetic diversity when a population is greatly reduced
Founder Effect
-When few individuals colonize a new habitat
Gene flow
-The movement of individuals between populations alters allele frequencies
Relative fitness
- An individual’s contribution to the next generation compared to others
- The fittest produce the most viable, fertile offspring & pass the most genes
Stabilizing selection
-Favors intermediate phenotypes, and acts against extreme ones
Directional Selection
-Acts against individuals of one of the phenotype extremes
DIsruptive Selections
-Favors individuals at both extremes
