SBI3U - Unit 3 - Evolution

Preparation

• Scientific Inquiry - An ongoing process that involves making observations, asking questions, forming hypotheses, making predictions, conducting investigations, making conclusions, and supporting or rejecting/revising hypotheses

  • Scientific Hypotheses - Tentative answers to testable questions based on observations

  • Prediction - The “if…then” statements made from observations about what you expect to occur during an investigation

  • Theory - An extensively tested hypothesis that encompasses a large body of information and that cannot be rejected after rigorous testing

• Science - An ongoing process for answering questions using scientific inquiry

• A well-controlled experiment has control groups, experimental groups, and replication

• Gene Pool - The total of all genes in a population

  • Genes can become varied through meiosis, random fertilization, crossing over, and mutations

• Population - A group of reproductively isolated organisms of the same species that live in the same place at the same time

  • Carrying Capacity - The maximum population size that a particular environment can support

  • Abiotic and biotic factors limit the growth of a population

• Adaptation - A characteristic that helps organisms survive and reproduce in their specific environment

  • They can be structural, physiological, or behavioural

• Fossil - The preserved remains of a once-living organism

• Extinction - A species that is no longer alive on earth

Adaptation and Variation

• Competition, severe weather, and famine can challenge an organism’s ability to survive

  • If the organisms that survived the challenges reproduce, their offspring will receive the genetic information that helped them survive

  • Genetic diversity and the interaction of organisms with their environments explains how populations change over time or become extinct

    • Diversity - Variation within a population

    • Extinct - The status of a species that has completely disappeared from Earth

• Adaptation - An inherited structure, behaviour, or physiological process that helps and organism survive and reproduce in a particular environment

  • Ex. hibernation, excellent vision, camouflage

  • Mimicry - A structural adaptation in which a harmless species resembles a harmful species in colouration or structure

    • This can help deter predators

  • Adaptations are the result of gradual, accumulative changes that help an organism survive and reproduce due to random, heritable mutations in genetic material

    • Variation - Differences between the inherited traits of individuals in a population, which may be structural, functional, or physiological

      • Not all variations are adaptations

      • Environmental conditions determine whether a variation has a positive effect, negative effect, or no effect on an organism

      • A positive variation will cause those organisms to survive more in a population, so that the variation becomes a frequent characteristic of the population

    • Interactions with the environment is important to adaptation and variation, because changing environments can cause some traits to be more advantageous

    • Physiological Adjustment - An organism’s ability to adapt during its lifetime to changing environmental conditions

  • The English peppered moth is an example of how proportions of inherited characteristics in a population change in response to changes in the environment

    • The moths can be light grey with black flecks, black, or an intermediate

    • Light grey moths were the most popular, but soon black moths became more prominent in urban areas

    • The light grey moths would camouflage with the light coloured lichen, but when the industrial revolution happened, the lichen died and the trees were covered in soot, allowing the black moths to camouflage instead

      • This meant that light grey moths were now more susceptible to predators

    • When the air became cleaner, and the lichen returned, the ratio of black moths decreased again

• Genetic variation in a population results from the variety of genetic information in all individuals of a population

• Mutation - A permanent change in the genetic material of an organism; the only source of new genetic variation

  • Mutations occur spontaneously from copying errors or mutagens when DNA is copied in S phase

    • Mutagen - Factors, such as UV radiation and chemicals, that can cause mutations

  • Mutations can cause a cell to exhibit characteristics or die

    • Mutations that significantly alter the shape or structure of DNA often adversely affect the well-being of an organism, but not all mutations are harmful

• A mutation in a somatic cell DNA will die with the individual organism

• A mutation in a gamete cell DNA can cause the mutation to be passed on by an allele to the next generation, and can affect the entire gene pool

• Selective Advantage - A genetic advantage that improves an organism’s chance of survival, usually in a changing environment

  • Over time, a selective advantage from a mutation causes the organism to be favoured in terms of biological success, which causes the advantage to become prevalent in the population

• Populations that reproduce quickly can pass on a new allele that may have been previously insignificant, but later proves to be an advantage

• Populations change, not individuals

  • Individuals can acclimatize, but not adapt

Natural Selection and Artificial Selection

• Natural Selection - The situational process by which characteristics of a population change over many generations as organisms with heritable traits survive and reproduce, passing their traits to their offspring

  • There must be diversity within a species for natural selection to occur

  • Certain traits are selected for or against by their environment

    • Selective Pressure - Environmental conditions that select for certain characteristics of individuals and select against other characteristics

      • This includes abiotic and biotic factors such as climate, predators, parasites, water, space and competition

      • When selective pressures change, the traits that are favourable change

  • Traits may be positive, negative, or neutral, depending on the current state of the environment

    • A population will slowly change to have more positive traits so they are better adapted to their environment

  • Fitness - How well suited an organism is to survive its habitat, and the relative contribution an individual makes to the next generation by producing offspring that will survive long enough to reproduce

    • A high degree of fitness means that an organism will survive and have a greater ability to reproduce so that it can pass on its advantageous genes

      • A high fitness organism will have many reproductively viable offspring (compared to the normal amount for a species) in the next generation

    • Harmful mutations reduce fitness, neutral mutations do not affect fitness, and beneficial mutations increase fitness

  • Natural selection can influence populations in three ways:

    • Stabilizing Selection - Extreme variations are selected against and the intermediate range phenotypes are retained in greater numbers, which results in decreased variation for the involved phenotype

      • Improves adaptation of the population to aspect of the environment that remain relatively constant

    • Directional Selection - The adaptive phenotype is shifted in one direction and one extreme phenotype is favoured over another

      • Common during times of environmental change or when a population migrates to a new environment

    • Disruptive Selection - Two phenotypic extremes are favoured, and intermediate forms are decreased

      • Intermediate phenotypes can be eliminated from the population, and the population is divided into two groups

• Artificial Selection - Selective pressure exerted by humans on populations in order to improve or modify particular desirable traits

  • For example, the Brassica oleracea was selected to create six very different varieties

  • Biotechnology - The use of technology and organisms to produce useful products

  • Artificial selection can breed plants and animals more suited for human survival

  • Artificial selection must be balanced to prevent organisms from failing in some aspect

    • For example, bulldogs have respiratory issues, and large dogs frequently have hip dysplasia

  • Domesticated organisms are typically bred to lack genetic diversity

    • Monoculture - Extensive plantings of the same varieties of a species over large expanses of land

    • This can be beneficial for manufacturing products to meet the needs of certain adaptations

    • However, because the organisms are so similar, a challenge that affects one individual will likely affect the majority of the monoculture

      • Gene banks preserve the seeds of early ancestors of modern plants, so if a modern plant nears extinction, genetic diversity can be introduced

Evolution

• The theory of evolution explains how biological diversity occurs, and how adaptations occur through natural selection

• Evolution - The slow, progressive change in the inheritable genetic traits within a population across generations

• Evolution occurs because the goal of every living organism is to survive and reproduce

  • Biological Success - When an organism lives long enough to reproduce and pass its genes on to its offspring

Evidence for Evolution

• Embryology - The study of embryos

  • Closely related species go through similar stages of development, although adults may not look similar

  • Similarities in embryos indicate that they share similar genes/common ancestry

    • For example, many vertebrates have gill slits as embryos, and pharyngeal pouches become necks in humans

    • Hind limbs in cetaceans stop being developed and degenerate in the fifth week of pregnancy

  • Amniotic eggs have the same fluid as sea water

    • Reptilian and bird eggs are waterproof, but amphibian eggs are not

    • Humans have extra-embryonic membranes

      • This allows the fetus to connect with the mother’s uterus

  • Deuterostomes - Embryos in which the anus is formed before the mouth

    • Both humans and Echinodermata are deuterostomes, indicating shared ancestry

• Vestigial and Homologous Structures

  • Vestigial Structure - Structures that are typically reduced and nonfunctional that were inherited from ancestors

    • They were once functional for survival, but are no longer necessary, and thus, no longer subject to natural selection

      • If they are unaffected by natural selection, they will be passed on unchanged through a lineage

    • For example, the pelvises of modern whales indicate that they evolved from species with hind limbs

  • Homologous Structures - Structures that are similar in fundamental layout and construction, although they may serve very different purposes

    • For example, pentadactyl limbs evolved into the current limbs of air-breathing vertebrates

  • Analogous Structures - Structures that have similar function, but were inherited or evolved independently from each other

    • For example, sugar gliders are marsupials, and flying squirrels are placental mammals, but they have similar features

    • This is due to similar selective pressures, but different gene pools

• Fossil Record

  • Fossils are found within layers of sedimentary rock

  • The succession of different groups at different times indicates that organisms have changed throughout time and descended from a common ancestor

    • A direct line of descent can be observed

    • Simpler organisms appeared earlier than most complex organisms

  • Foraminifera, small oceanic protozoans, leave a continuous fossil record in ocean sediments, which can trace their gradual evolution

• Biogeography - The study of the past and present geographical distribution of species

  • The distribution of living plants and animals suggests organisms with adaptations for one environment can invade a new environment and develop specific adaptations to new conditions

  • Closer areas are more populated by closely related species than areas that are geographically separated

  • Animals on an island resemble animals on the closest continent or mainland

  • Fossils of the same species can be found on the coastline of neighbouring continents

• DNA and Modern Evidence

  • Relationships between organisms can be determined by similarities in DNA

  • Similar DNA patterns indicate inheritance from a common ancestor

  • Before DNA analysis, phylogenetic trees described evolutionary relationships by anatomy

    • As DNA technology develops, evolutionary trees change to reflect recently understood relationships

  • Understanding evolution is important for observing natural selection and combating disease

  • For example, the bird family Cotinga has many different species that varied greatly, but DNA evidence showed how morphologically different birds were available

  • For example, the increased resistance of mosquitoes to insecticide caused an increase in malaria in humans

  • The more closely related two species are, the less different their DNA will be due to less time for mutations to occur

  • The more distant species are, the more different their DNA will be due to more mutations

Understanding Evolution

• Carolus Linnaeus

  • Named species by perceived relationships based on structures, indicating a common ancestor and creating an evolutionary framework

• Thomas Malthus

  • Principle of Population - Every species has more offspring that can be expected to survive, because external factors will lower populations

• Buffon and Lyell

  • Uniformitarianism - The theory that changes in the earth’s crust during geological history have resulted from the action of continuous and uniform processes

    • Geological processes in operation now operated similarly in the past

    • It requires vast amounts of time to explain the present state of the earth

• Jean Baptiste Lamarck

  • The first comprehensive theory of the mechanism of evolution

  • He proposed that interactions of organisms and the environment drove the process of evolution

    • He believed characteristics acquired during an individual’s lifetime could be passed on to one’s offspring, and patterns of use and disuse drove the adaptations

      • This is called the Inheritance of Acquired Characteristics

• Charles Darwin

  • He published “On the origin of species by means of natural selection” after his voyage on the Beagle

    • All species evolved from earlier species

    • An overproduction of a species occurs to replace dying individuals

    • Individuals show variation, which may be more favourable than others

    • Natural selection favours the best suited at that time, so that they can have more offspring

    • The best fit adaptations are inherited from the surviving individuals

• Alfred Russel Wallace

  • A naturalist and explorer that developed essentially the same theory as Darwin

  • The Wallace and Weber lines are used to mark the difference of animals between Australia and Southeast Asia

Factors Affecting Evolution

• Microevolution - Factors that affect populations, and result in changes to gene frequencies in a population due to reproductive isolation

• Natural Selection

  • The process that allows organisms that are best acclimatized to their environment survive and reproduce, resulting in those that are less fit to die out

  • Non-random

  • Some individuals have greater reproductive success because they possess alleles that make them more fit for their environment

  • This can lead to significant changes in populations over many generations

• Sexual Selection - The mating among individuals based on selecting for specific phenotypes, behavioral or physical, or the resources the mate can provide

  • Non-random

  • Desirable individuals leave more offspring, which leads to more offspring with certain alleles that have improved fitness

• Mutation

  • Random and non-adaptive

  • Mutations are the only source of additional genetic variation and new alleles or genes

  • Can be caused by unrepaired changes in DNA or chromosome breakage/rejoining in meiosis

• Gene Flow - The movement of alleles from one population to another population

  • Random and non-adaptive

  • Organisms bring or remove alleles when they enter or leave a population

  • This changes the allele frequency of both populations, and leads to reduced genetic differences between populations

• Genetic Drift - The random change in genetic variation based on chance

  • Random and non-adaptive

  • Anaphase I is an example of how the random assortment of DNA can result in a shift

  • It does not take into account the benefits or harms of an allele

  • Some alleles may be lost, and some may be fixed (rise to 100% frequency)

  • Random chance is the strongest in small populations, and larger populations are more resistant to chance events changing the allele frequency

  • Bottleneck Effect - The rapid reduction of alleles in a population resulting from an environmental or human caused change

  • Founder Effect - When several individuals separate from a large population and establish a new one

  • If gene pools are separated for long enough, adaptive radiation and speciation may occur

Patterns of Evolution

• Divergent Evolution - Evolution towards different traits in closely related species

• Convergent Evolution - Describes evolution toward similar traits in unrelated species

• Coevolution - Two or more species can evolve together, where evolutionary paths become connected, and species evolve in response to changes in each other, and can occur in competitive or beneficial relationships

  • Batesian Mimicry - A harmless species evolves to imitate the warning signals of a harmful species, directed towards a common predator

  • Mullerian Mimicry - Two or more unrelated distasteful/harmful species evolve to mimic each other’s warning signals to ward off a common predator

    • If two species look similar, a predator will only have to try one species to associate a warning signal with both species

    • The more common a morph is, the higher the fitness

Hardy-Weinberg Genetics Calculations

• Hardy-Weinberg Equilibrium - States that allele frequencies in a population will remain constant in the absence of evolutionary influences

• To calculate allele and genotype frequencies in populations, use the equation:

  • (p + q)² = p² + 2pq + q² = 1

    • p = Frequency of allele A (dominant)

    • q = Frequency of allele a (recessive)

    • p² = Frequency of AA (homozygous dominant)

    • 2pq = Frequency of Aa (heterozygous)

    • q² = Frequency of aa (homozygous recessive)

  • The sum of the frequency of both alleles should equal 1

  • It is easier to calculate off of the recessive phenotype, since the genotype is already known

• Conditions:

  • No directional mutation

  • Reproductive success/no natural selection/equal fitness

  • Random mating/no sexual selection

  • Large population/no genetic drift

  • No immigration or emigration/no gene flow

• By comparing genotype frequencies from one generation to the next one, one can learn whether or not evolution is occurring, in what direction, as well as the rate of evolution for the selected trait

• It cannot tell you the cause of change in the gene pool

Speciation

• Macroevolution - Major changes above the species level that leads to the formation of new species due to reproductive isolation

  • Reproductive Isolation - When the gene pool of a certain population becomes isolated or protected by geographical, behavioural, physiological, or genetic differences, and can no longer successfully breed

• Speciation - The formation of a new species from existing species that occurs when members of a population change so much that they can no longer produce viable offspring with members of the original population

  • Allopatric Speciation - An extrinsic mechanism that occurs due to geographic isolation that prevents mating between members of the same species

    • Over time, the two isolated populations evolve as they adapt to new environments

    • More likely to occur in populations located in the edge of a habitat, and are more likely to become subject to the founder effect

  • Sympatric Speciation - An intrinsic mechanism where a new species evolves from an ancestral species in the same geographic area as a result of reproductive isolation

  • Adaptive Radiation - The process in which organisms diversify rapidly from a common ancestor to many different forms and species

    • Happens when a single species evolves into multiple species to fill different ecological niches

      • Specialists fill very specific niches, and generalists fill more general niches

    • In the case of Darwin’s finches, the birds filled unoccupied niches on the Galapagos, and each bird evolved to fulfill the niche of their specific island

• Gradualism - A model of evolution that views evolutionary change as slow and steady before and after divergence from a common ancestor

  • This is rarely seen in the fossil record

• Punctuated Equilibrium - A model of evolution that views evolutionary history as long periods of stasis that are interrupted by periods of divergence

  • This pattern is seen in the fossil record

• Environmental influence can cause species to go extinct

  • Extinction - The elimination of a species from Earth

  • Extinctions affect a few species in a small area

  • Extinctions occur at roughly the same rate as speciation

  • Mass extinctions destroy many species at a global level caused by catastrophic events

    • At least five mass extinctions have happened in the last 600 million years

  • Human events can cause severely fragmented populations that may be driven to extinction from a lack of genetic diversity, and thus a lack of evolution and adaptation

Check List

Textbook

• Read pg 290-293, #1-13, 18-25, 27-35

• Read pg 296-299

• Read pg 300-311

• Pg 299 #2,3,6

• Pg 304 #1,2,10

• Pg 307 #9

• Pg 311 #2

Biozone 1

• Pg 306-307

• Pg 324-326

• Pg 329-330

• Pg 343

• Pg 359

Course Pack

• Pg 87-99

• Pg 113-114

• Pg 115

• Pg 128-131

Powerpoint

• 1 - Introduction to evolution part 1

• 2 - Introduction to evolution part 2

• 3. Evidence for Evolution

• 4. Mechanisms and Patterns of Evolution

• Mechanisms of Evolution + Speciation

• 5. Speciation

• 6. Review of Biozone Pages

Other

• Stated Clearly

• Crash Course: When Darwin met Mendel

• TVO Videos on Organic Evolution