Evolution, Natural Selection, and Evolutionary Theory Flashcards
What are the 3 themes that run throughout earth’s history?
- plate tectonics
- geologic time
- evolution
What is evolution?
Changes in heritable traits in populations (groups of individuals of the same species that live together) over time
- “descent with modification” Charles Darwin
- can result in new species
What is a heritable trait?
something that can be passed down from a parent to offspring
Explain how Darwin and Wallace proposed the theory of evolution
Alfred Russell Wallace was a naturalist who came up with the same ideas as Darwin > their ideas were very against the ideas of the time (that species were fixed)
1859: jointly published their views on evolution and proposed natural selection as the mechanism for evolutionary change
- both observed variation in natural populations > independently came up with the idea that natural processes select favourable individuals from populations for survival
Explain Darwin’s trip to the Galapogas islands and the two major observations he made
2 species he observed (tortoises and finches) that were similar to what he saw on mainland Ecuador but with some variations
Tortoises:
- two diff types of shells for diff feeding habits:
- Saddle shells = for a low, arid island with less vegetation = eating flowers on cacti - have to lift necks up to get it
- Dome shells = for a high, lusher island with lots of vegetation = don’t need to lift heads up to get food
Finches:
- different beaks for diff eating habits
- Those eating insects have small pointy beaks
- Those eating seeds and nuts have thicker beaks better for crushing
What is the significance of natural selection? What does “survival of the fittest” mean
Natural selection is a mechanism for evolution
- organisms possess heritable variations
- not all young survive to maturity > those with the favourable variations are more likely to survive to reproduce and pass on their favourable variations
Survival of the fittest > involves inheritable variations leading to differential reproductive success
What is the moth example of natural selection
Prior to the industrial revolution the moths were light coloured
After industrial revolution and pollution, more dark coloured moths to blend in with soot covered things - better able to hide from predators → natural selection favouring the dark coloured moths → “survival of the fittest”
What is artificial selection?
Selective breeding of domestic animals and plants
Explain Mendel’s experiment and the birth of genetics
(what are traits controlled by)
(what are alleles)
1860s: Mendel’s breeding experiments with garden peas showed how variation is maintained and passed on
> traits are controlled by a pair of factors (genes)
> alleles: alternate forms of genes that control the same trait > dominant and recessive alleles
> genes that control traits do not blend during inheritance > genes are not lost even though not expressed in every generation
How many sets of chromosomes do humans have?
24 sets of chromosomes
What is the basic unit of heredity?
The gene
Explain the context of a gene
It is a segment within a strand of eukaryotic DNA, that is organized into the paired chromatids of a chromosome
- expressed as traits or held in a recessive state (no expression)
In the context of eye colour, what is the gene and what is the allele?
gene = eye colour
allele = brown or blue
What do we need to know about Mitosis?
- used for almost all cell division needs
- adds cells during development and replaces worn-out cells during life
- goal: produce daughter cells identical to starting cells
What do we need to know about Meiosis?
- production of gametes (sex cells: sperm & eggs / pollen & ovules in plants)
- goal: produce daughter cells with exactly half as many chromosomes as the starting cell
- sexual reproduction enables reshuffling of genes from generation to generation; creates variations that natural selection works on
- variation of traits that already exist
What brings about new variations in mutations? What are the two kinds of mutations and what causes them?
Changes in chromosomes/genes/the hereditary information
- chromosomal mutations > affect a large segment of the chromosome
- point mutations > affect a single gene
*may be harmful, beneficial, or have no effect
*caused by mutagens: chemicals, radiation, or temperature extremes
*or can be spontaneous
What accounts for variation in people? What is genetic drift?
Sexual reproduction and mutations account for most variations in populations
Genetic drift = a random change in a gene in a population is due to chance - affects small populations more than large
What is the modern synthesis or neo-Darwinism view of evolution?
- early 20th century: genetics was included in evolutionary thinking
- natural selection was reaffirmed
- ideas of genetic drift emerged
- importance of mutations were realized
What is the significance of the tree of life?
The relationships between organisms can be represented by a single branching tree
- species are clustered into groups with similar traits
- all extinct and extant species can be traced back to a single common ancestor
- shows how intertwined and not linear evolution is
What are species and speciation (two models)?
Species = natural populations of similar individuals that can interbreed and produce fertile offspring
- asexual organisms are excluded here
Speciation is the formation of a new species from ancestral ones
Different models:
- phyletic gradualism
- punctuated equilibrium
Explain Punctuated equilibrium (what was it based on) and Phyletic gradualism?
Punctuated equilibrium:
- first suggestion of evolution
- for long period of time, a species remains the same or pretty much the same > not much change in morphology over time for this species
- rapid change is what causes a new species
- based on our fossil record - but we now know that much of our fossils record is incomplete - missing fossils for those internal changes
Phyletic gradualism:
- bending line suggests a species makes gradual/minor changes in traits over time, and eventually enough changes occur that it branches off into a new species
Explain allopatric speciation? What are potential barriers?
- a few individuals of a species on the mainland reach isolated island 1 > speciation follows genetic divergence in a new habitat
- later in time, a few individuals of the new species colonize nearby island 2 > in this new habitat, speciation follows genetic divergence
- speciation may also follow colonization of islands 3 and 4 > and it may follow invasion of island 1 by genetically different descendants of the ancestral species
*isolated population no longer exchanges genes with the parent population
*potential barriers = remote areas, rising mountains, rising sea level
Explain the significance of extinctions - good and bad?
- 99% of all species that ever lived are extinct
> background extinctions are ongoing (natural comings and goings of species)
> mass extinctions are more rare but kill species more quickly - rate that their dying is quicker than rate that they’re reproducing or evolving - mass extinctions occur periodically
- extinction also gives rise to opportunities for the evolution of new species
ex. extinction of dinosaurs opened up new areas for mammals to move into and flourish - less competition for them
What is microevolution and macroevolution?
microevolution: evolutionary changes within a species
ex. organisms developing resistance to insecticides
macroevolution: involves changes such as the origin of new species
ex. amphibians evolving from fish
*microevolutionary effects account for macroevolution
What is divergent and convergent/parallel evolution?
Divergent:
- refers to an ancestral species giving rise to a diverse range of other species
Convergent/parallel:
- convergent = Similar characteristics evolving in distantly related organisms due to similar environmental pressures > different ancestral phenotypes
List the 3 evidences for evolutionary relationships
- Embryology
- Homologous structures vs Analogous structures
- Vestigal structures
What is Embryology?
- Study of development of embryos
The embryos of many vertebrates are similar for most of development
- Believed to be a result of common ancestry
What are homologous structures and analogous structures?
Homology: presence of anatomical structures in different groups of organisms that have the same ancestral origin, but now serve different functions
ex. limbs of humans, cats, whales, and bats > bulit upon same bone structure
> result of divergent evolution
Analogy: body parts, such as wings of insects and birds, that serve the same function but differ in structure and development > they don’t result from a common ancestral feature
ex. fins and wings
> result of convergent evolution
What are vestigial structures?
They are biological features that have lost their original function through evolution > often reduced in size and can be evidence of common ancestry between species
ex. declaw > useless toes on back of dog paw
ex. tailbone on human - sometimes appear in a baby and is surgically removed
What are cladistics? Compare a phylogenetic tree and a cladogram
Grouping organisms based on derived characteristics
Phylogenetic tree shows evolutionary relationships among groups of organisms
- shows anatomical differences over time
Cladogram shows the relationships among members of a clade
- depicts shared traits among clades - hypothesizing relationships
What is a clade?
A group of organisms believed to have evolved from the same ancestors
