EVOLUTION Flashcards
Theory
- Every day language = educated guess
- Sciences = explanatory model that accounts for a very large body of evidence
- Scientific theories provide basis for explaining observations of the natural world and for making testable predictions
Evolutionary Theory (general)
- All life forms are fundamentally similar at cellular and molecular level
- Evolution explains the history of life on earth
- Evolution is the process by which organisms change over time
Evolution of Evolutionary Theory
(important people)
Aristotle (384 - 322 BCE)
Georges-Louis Leclerc de Buffon (1707-1788)
Carl Linnaeus (1707-1778)
Erasmus Darwin (1731-1802)
Chevalier Lammark (1744-1829)
Charles Darwin
Early Theories: Aristotle
- Most Europeans accepted the idea that all living things had been created in their present forms and were immutable
- They could not change and had not changed
- All natural phenomena developed through strongly held religious beliefs
Early Theories: Buffon
- Applied scientific methods to the detailed study of anatomy
- Studied animal structures
- Considered their functions
- Puzzled by some features that seemed to have no purpose
- E.g. he studied pig toes, they have toes that don’t reach the ground
Evolutionary Theory: Linnaeus and Erasmus Darwin
- Proposed life changed over time
- Erasmus (Charles Darwin’s grandfather) suggested life might have evolved from a single original source
How old was the world originally thought to be, and what contradicted this belief?
- Scientists thought would was 1,000 years old
- Scientists began to find fossils, which contradicted this belief
Fossils
Any ancient remains, impressions, or traces of an organism or traces of its activity that have been preserved in the Earth’s crust
* Fossils dated back to minimum age of 1,000 years
Preserved materialized remains of organisms
* The closer to the surface, the more recent the ancestor
* Organisms die and become trapped in sediments
* Fossilization is a comparatively rare event
* Fossil record is incomplete
Palentology
Study of fossil organisms to learn about prehistoric life
* Cuvier (1769-1832) was a paleontologist
Geology
Study of the Earth’s physical structure
* Lyell (1797-1875) was a geologist
Cuvier
Through study of paleontology, noted the following:
* Fossils of very simple organisms are found in all depths of fossil deposits
* Fossils of more complex organisms are found only at shallow depths in younger rock
* Fossils in shallower depths are more likely to resemble living species
* Rock layers contain fossils of many species that do not occur in layers above or below them
Catastrophism
- Fossil observation offered strong support that life evolved from simple to complex
- Cuvier believed that species themselves didn’t change
**Catastrophism **= global catastrophes, such as fossils, caused the widespread extinction of species
* Cuvier believed these speicies were then replaced w another newly created set of species
Uniformitarianism
- Charles Lyell (father or modern geology)
- 1830 - put forth his theory/principles of uniformitarianism
**Uniformitarianism = **
* Earth has been changed by same processes in the past that are occurring in the present
* Geological change is slow and gradual, rather than fast and catastrophic
* Natural laws that influence these changes are constant and eternal, they operated in the past w the same intensity they do today
* Lyell’s theories directly challenged belief in a young Earth (1,000 years old or less)
Evolutionary Theory: Lamarck
- Student of Buffon
- First scientist to offer a mechanism for the evolution of a species
- Evolutionary change resulted from two distinct principles:
- Use and disuse
- Inheritance of acquired characteristics
Lamarck’s First Principle: Use and Disuse
Structures an individual uses become larger and stronger while structures not used become smaller and weaker
* E.g. athlete’s muscles increase in size (structures in use), astronauts returning home have reduced muscles from lack of use (structures not in use)
Lamarck’s Second Principle: Inheritance of Acquired Characteristics
Individuals pass down characteristics acquired during lives
* E.g. if adult giraffe stretched its neck during its lifetime, then its offspring would be born w slightly larger neck
Lamarck’s Findings
Though Lamark’s theory was flawed, he made significant contributions to our understanding of evolution
* All species evolve over time
* A species evolves in response to its environment and becomes better adapted to that environment
* E.g. bunnies fur turns white in winter, helps blend in w snow and hide from predators
* Changes are passed from generation to generation
Charles Darwin
- By the 19th Century, there was growing evidence that Earth was old
- Ideas of the history of the Earth and its life-forms were being challenged
- Charles Darwin linked ideas from paleontology, Geology, geography biology, and his own observations to come up w a mechanism of evolution: Natural Selection
Who was Charles Darwin
- Born in 1809 in Shropshire, England
- Son of a local doctor and wedgusod heiress
- Parents wanted him to study medicine
- Found more interest in natural word
Voyage of the HMS Beagle
In 1831 at 22, Darwin set sail on HMS Beagle for a 5 year trip to record and collect specimens for the British Navy
* They had hoped that Darwin would find evidence of biblical creation
On his voyage, Darwin:
* Collected thousands of specimens
* Collected fossils that resembled existing animals
* Volcanic Galapagos Islands had species similar to South American natives
* Made most discoveries in galapagos
* Species differed from island to island
Patterns in Diversity
- Species vary globally: species varied depending on where they lived on Earth
- Species vary locally: species had different features depending on local habitat
- Species vary over time: species evolve from one common ancestor
- Become different creatures over time
- Geological change
Darwin’s Finches
- Collected on galapagos
- Beaks modified to suit food source
- Descended from common mainland ancestor
- Different species formed on separate islands
- New species branch out from old ones
Evolution/Descent with Modification
- Darwin proposed descendants of the earliest organisms spread into various habitats over millions of years
- Species changed over time based on adaptations to their environment
- E.g. brown hare (woodland area) → white coat of fur in snowy climate
- White rabbit fatter to keep warm in winter
Survival of the Fittest
- Fitness of an individual is ability of an individual to survive and reproduce in its environment
- Individual w adaptations survive and reproduce
- Survival of the fittest
- Natural selection
Pathway to a Theory
(Darwin)
- 1837 returns to England
- “Transmutation” of species
Artificial selection - Bred pigeons
- Experiments in gardens and greenhouses
- Environments have similar selective effect
Struggle for survival - More offspring produced than can survive to reproduce, favoured variations reproduce
- 1858 receives paper from wallace
- 1859 published “on the origin of species”
Evidence for Darwin’s theories
Homologous vs analogous structures
Embryonic homologies
Vestigial structures
Homologous Structures
Share a common evolutionary origin, not function
* E.g. human, cat, whale, and bat all contain similar bone structures, but different function
Share a more recent common ancestor
* E.g. forelimbs of terrestrial vertebrates. Whale flippers are human forelimbs
Analogous Structures
Share similar function, but not origin or structure
* E.g. bird and bee wing
Vestigial Structures
Rudimentary or non-functioning structures that are present in reduced form → humans have 17
* These structures had importance in past → no longer have active functions
* Changing environmental conditions no longer favour the selection
* E.g. whale pelvis, appendix in humans
Artificial Selection
- Darwin searched for examples of selection pressures among domestic animals
- Breed pigeons for certain traits → similar to how we manipulate dogs
- Selected traits may be bred in relatively few generations
- Environment provides selection pressures in the wild
Struggle for Survival
- Thomas Malthus Essay on principle of population
- Organisms produce more offspring than are able to survive
- Favourable variations would tend to be preserved; unfavourable variations die out
Natural Selection
- Published: On the Origin of the Species in 1859
Individuals vary in population - Favourable variations result in traits being passed on
- Survival is not random
- Sheer weight of Darwin’s research and observations make theory hard to refute
Artificial Selection (Bacteria)
Artificial selection = selective breeding of domesticated plants and animals to produce offspring w genetic traits that humans value
* Has occurred for many years
* Darwin observed that artificial selection could produce great deal of change in species over a short period of time
* Cous Odder = equivalent to a human women’s breast tissue
Issues with Artificial Selection
- Traits for desire, rather than purpose (medical issues): German sheperd hips, Pug noses, Pug heads
- Playing “God” w unknown ripple effect consequences
- Decrease genetic diversity
- Create monocultures that can be wiped out by one disease
Antibiotic Resistance in Bacteria
TB, Tuberculosis
* Caused by rod-shaped bacterium, Mycobacterium tuberculosis
Streptomycin
* Developed in 1940s to treat TB
* By 1970s it was almost completely eradicated
In 2006, outbreak of extensively drug-resistant tuberculosis strain in KwaZulu-Natal in South Africa
* By 2008, it had spread to over 49 countries
* Over ⅓ of world’s population was affected
How does antibiotic resistance occur?
* Natural selection
* Antibiotic discovered between 1940 and 1950 by Alexander Flemming
Natural Selection in TB
- Patients prescribed antibiotics for 6-9 months to cure
- Some patients do not complete treatment
- Bacteria still hanging around end up surviving, duplicating, and passing on their now new resistance to this treatment
- These bacteria have survived through natural selection
Modern Synthesis
- Darwin had no concept of the actual mechanism of inheritance
- Genetics now, is heavily integrated into evolutionary theory
- Organisms vary by number of genes
- Large genomes present more opportunities for mutation = More chance for error
- Sexual reproduction increases variation compared to asexual reproduction/mitosis
Genes vs Alleles
- Genes = unit of inheritance that governs the character of a particular trait
- Segment of DNA coding for single polypeptide
- Alleles = alternate forms of the same gene
- E.g. there is one gene that orders for eye colour and different alleles on that gene will determine the colour of the eye
Homozygous vs Heterozygous
Individuals of a given trait can either be:
Homozygous dominant = 2 copies of dominant allele
* Individual shows that trait → e.g. BB = brown eyes
Homozygous recessive = 2 copies of recessive allele
* Individual shows recessive trait → e.g. bb = blue eyes
Heterozygous = 1 copy of the dominant allele, 1 copy of recessive allele
* Individuals show dominant allele → e.g. Bb = brown eyes
Gene Pools and Variation
- Gene pool = consists of all the alleles in all the individuals that make up a popu;ation
- Phenotype = an organism’s expressed trait → i.e. one that you can see
- Genotype = traits that an individual has that have been acquired from parents
Hardy-Weinberg Equilibrium
Population not undergoing change do not evolve
* HWE quantifies genes by measuring allele frequency
* HWE requires constant conditions
HWE occurs only if all the five conditions are met:
* Population very large
* Random mating
* No mutations occur
* No migration occurs (gene flow)
* No natural selection occurs
p^2 + 2pq + q^2 = 1 and p + q = 1
p^2 = frequency of AA genotype
2pq = frequency of Aa genotype
q^2 = frequency of aa genotype
Why Study HWE
- HWE is not realistic and does not occur in real life
- In nature, HWE doesn’t occur for long periods of time
- Concept is useful as it provides a “no change” baseline
- Makes it possible to recognize when gene pool is changing
- If 5 above conditions are not met, then genetic equilibrium is distributed and gene pool frequencies may change
- When gene pool frequencies of alleles change within a population
- Called microevolution = evolution on a small scale
Types of Microevolution without Natural Selection
(list)
- Genetic Drift
- Gene Flow
- Mutations
- Selection
Genetic Drift
- Changes to allele frequency by chance in small populations
**Bottleneck effect = **dramatically reduces population, and thus the gene pool due to natural disaster - By chance, only certain allele are represented
- This decreases genetic variation in a population
- Reduces population ability to adapt to environmental change
Founder effect = individuals leaving a population to establish a new one (a few individuals leave one area and they colonize a new area) - The smaller the colony, the smaller the genetic gene population
- The change in allele frequencies of this new population relates to the genetic makeup of the founders of the colony
Gene Flow
Genetic flow is a random process
* Involving exchange of genes with another population, when retile individuals migrate between populations
* Movement of genes in or out of population disrupts genetic equilibrium
* Also reduces genetic differences between populations
Mutations
- Source of new alleles
- May be neutral, harmful or beneficial
- Affects the fitness of individual
- Harmful mutations usually result in death of gamete
Selection
- Natural + artificial; source of variation
- Mutation provide variation in traits that are selected by outside influences
- Natural selection acts on individual phenotypes which are passed on to subsequent generations
- Variation environments favour multiple phenotypes
Types of Microevolution with Natural Selection
(list)
- Stabilizing Selection
- Disruptive Selection
- Directional Selection
- Sexual Selection
Stabilizing Selection
- Where the average phenotype is favoured
- Selection against individuals exhibiting variation in a trait that deviates from the current average
- Most common form of selection
- Phenotypic extremes are selected against → e.g. human birth weights
- Stabilizing selection = culls extreme variations from the population
- E.g. eliminating individuals that are unusually light or dark
- Trend towards phenotypic variation and maintenance of the status quo
Directional Selection
- Directional selection = selection that favours an increase or decrease in a phenotypic trait
- Common in artificial selection where we select favourable traits
- Can follow dramatic follow dramatic change in environment → e.g. migration, flood
- Individuals at one extreme are more successful in future generations → e.g. peppered moth, hummingbird bill length
- Directional selection shifts the overall makeup of the population by favouring variants of one extreme → e.g. trend towards darker colour, perhaps bc landscape blackened by lava
Disruptive Selection
- Selection favours 2 or more variations that differ from the population average
- Usually at two extremes of the trait
- Environmental change produces two distinct food sources
- e.g. hummingbird bill length, tall and short flowers are a good source for short billed and long billed hummingbirds, but not medium billed hummingbirds
- Birds on the extreme ends of this trait will be more successful and contribute more offspring to later generations
- Diversifying selection favours variants of opposite extremes over intermediate individuals
- E.g. relative frequencies of very light and very dark snails have increased. Perhaps snails have colonized a patchy habitat where a background of white snd is studded w lava rocks
Sexual Selection
- Favours selection of any trait that a partner deems valuable
- Continued selection has resulted in sexual dimorphism or physical differences in the sexes
Female mate choice - Bright colours, behaviour, physical traits
Male competition - Evolved physical traits to aid in sexual competition e.g. antlers
- Fight to gain control over territory that is home to females they can mate with → e.g. peacock tails, fiddler crab claws
Cumulative Selection
- Evolution of complex features
- Mutations are a result of chance, natural selection is not
- Accumulation of favourable mutations results in complex structures such as the eye
Altruism
- One organisms benefits from another’s behaviour
- Believed that well-being of others is greater than the survival of oneself
- E.g. insect colonies (workers vs queen) birds (care and feeding of young), monkeys and humans
- Kin selection and care increases chance of genes being passed on
