Unit 5: Evolution (slideshow notes)

What is evolution?

• A change in the genetic make-up of a population over time

• Supported by multiple lines of evidence

THE CHANGE IN THE ALLELE FREQUENCY OF A POPULATION OVER TIME

Early Ideas of earth

• Earth is young

• Earth is unchanging

What year and Who proposed the theory of Gradualism

James Hutton (1788)

What is gradualism

earth was formed entirely by slow-moving processes, such as erosion and sedimentation, and that these slow forces continue to shape the landscape

Who and when was the theory of catastrophism invented

George Cuvier (1796)

What is the theory of catastrophism

• major changes to earths crust were due to catastrophic vs gradual changes

• species can become extinct

• species can change over time

What did palaeontology find

Found that fossils were dissimilar to modern life

Who wrote the essay on the principle of population

Thomas Malthus (1798)

What did Thomas Malthus describe

described competition as a struggle for survival

Who proposed the theory of Uniformaitarianism

Charles Lyell (1830)

What does Uniformitarianism say

• Changes to earth is uniform

• land masses change over immeasurable time

• earth is ancient

What did Jean Baptiste Lamarck (1809) do

• He looked at fossil records and role of environment

What did Jean Baptiste Lamarck (1809) propose

Idea 1: Use and disuse

• use: gets enhanced over time

• disuse: loses over time

Idea 2: Inheritance of aquired characteristics

• these traits get passed on

What is Charles darwin famous for

His theory in evolution: Natural Selection (1837)

Whats an important location that Darwin and Fitzroy went to

Galapagos islands

• Islands’ important factors:

  • isolation

  • new/different/unique populations found no where else

What did darwin notice about the animal species that lived on galapagos islands

• they resembled species living on the south american mainland

What did Darwin hypothesize based on what he saw on the galapagos islands

Hypothesized that the islands had been colonized by plants and animals from the mainland that had then diversified on the different islands

Darwin’s Finches, what was special

He was amazed to find out that ALL 14 species of birds that he found were finches

• but there was only ONE specie of finch on the mainland

Essense of darwin’s ideas (5)

1. Variation exists within population

2. Competition for limited resources results in differential survival

3. individuals with. more favorable phenotypes are more likely to Surive and Reproduce

4. Evolutionary fitness is a measure of reproductive success

5. Changes in environment causes changes in selection

Darwin finches explained..(3)

• Variation in beak sizes and shapes exist within mainland population of finches

• Changes in food availability lead to changes in competition among individuals

• individuals that could forage for food more successfully (ideal beak phenotype) were more likely to survive and reproduce

  • the other individuals either died or moved to a different environment (an island)

• Over many generations the population diversified

whats speciation

when populations diversify over many generations

What did darwin do when he returned to england in 1836

• he wrote “secret” papers describing his collections and observations

• he completed a draft of his theory of specie formation in 1844 but was reluctant to publish it

Who is alfred russel wallace

• a young naturalist working in the east indies

• had written a short paper with a new idea

• he asked darwin to evaluate his ideas and pass it along for publication

What was darwins book titled

The origin of species by means of natural selection

What is the process of natural selection according to Darwin? (4)

• There is a natural variation in populations

• Competition for limited resources results in differential survival

• Individuals with more favorable adaptations are likely to survive

  • more likely to produce more favorable offspring

    • more likely to pass traits on to the next generation

• Selection is based on the environmental conditions

Individuals are selected and populations evolve!

(with darwin theories, DONT MENTION DNA OR GENES)

Natural selection Mnemonic

ICE AGE

What does “I” stand for in the natural selection Mnemonic

• Inherited variation exists within the population

What does “C” stand for in the natural selection Mnemonic

• Competition results from an overproduction of offspring

What does the E stand for in the natural selection Mnemonic

• Enivoronmental pressures lead to differential reproduction

What does the “A” stand for in the natural selection Mnemonic

• Adaptations which benefit survival are selected

What does the “G” stand for in the natural selection Mnemonic

• Genotype frequency changes across generations

What does the “E” stand for in the natural selection Mnemonic

• Evolution occurs within the population

Where does variation come from?

Mutation + Sexual reproduction

Where does variation come from? (mutations)

• random changes to DNA

  • errors in mitosis and meiosis

  • environmental damage

Where does variation come from? (sexual reproduction)

• Mixing of alleles

  • recombination of alleles

    • new arrangements in every offspring

  • new combinations = new phenotypes

• Spreads variation

  • offspring inherit traits from parent

Why is variation important? (in terms of Fitness?)

• Fitness is the survival + reproduction success of individuals

  • individuals with certain phenotype variations leave more or less surviving offspring

  • depends on abiotic and biotic factors that can be more or less stable

  • affects the rate and direction of evolution

What is artificial selection

• selective breeding

  • humans select traits in organisms that are desirable

    • organisms with common traits are crossed

    • leads to a change in the allele frequencies in a population over time

• operates on the natural variation that exists in the population

What do evolutionary biologists refer to an “adaptation” as?

• a genetically controlled trait that evolved as a result of natural selection

  • increases the fitness of an organism

short term for acclimitization

do not involve genetic change

Structural adaption

• anything that has to do with the body structure

• characteristics of body form including skeleton, size, shape, number of limps, body covering, and so on

Eg. spines on cactus protect against herbivores

Physiological adaptations

• Deal with the individuals physiology

  • internal/cellular responses to stimuli

  • chemicals they may produce

Eg. spiders produce silk for web

• spiders

• snakes

• plants

• insects

behavioural adaptations

• Combinations of structural and physiological adaptations that make the behavioural response to stimuli possible

eg. hunting behaviour results from colouration, strength and speed, or stealth to catch food

• hunting

• avoiding

• migration

types of natural selection

• stablizing selection

• directional selection

• disruptive selection

stablizing selection

• favours individuals with an “average” value for a trait

• selects against those with extreme values

• tends to keep allele frequencies relatively constant, thereby limiting evolution

Example: human birth weight

Directional selection

• favours individuals with a trait at one extreme of distribution

• selects against the average and the other extreme

examples:

• the progressive change in coloration of peppered moths

• antibiotic-resistant bacteria

Disruptive selection

• Favours individuals at both ends of the distribution

• selects against the average

• It is also known as diversifying selection

• leads to the formation of distinct subpopulations of organisms

• in time, the allele frequencies in the subpopulations may change to the extent that the two groups may no longer be able to interbreed —> speciation

• Example: darwins finches (beak sizes)

What is Microevolution

describes changes to the alleles frequencies within a population of a single species over time

Example of microevolution

Industrial melanism

• Peppered moth has variation in the body colour

• found in all parts of england

  • prior to industrial evolution

    • mostly light, peppered variety

  • following the Industrial Revolution

    • mostly the dark variety

• selection pressure —> Predation

What is Macroevolution

Refers to large-scale and long-term evolutionary changes leading to the formation of new species

What is selective pressure

predation / predator

• an evolutionary force that causes a specific phenotype to be more favorable in certain environmental conditions.

Example of macroevolution

• the extinction of the dinosaurs

• darwins finches

What is population Genetics?

• The study of genetic variation within populations

• measures changes in the allele frequencies in a gene pool

What is a population

A population is a group of individuals that are part of the same species in the same area at the same time

What is a gene pool

the collection of alleles in a population

what is allele frequency

how common an allele is in the population

• how many A vs a in a whole population

the 5 agents of evolutionary change

1. mutation and variation

2. gene flow

3. non-random mating

4. genetic drift

5. selection

describe the impact of mutation and variations

mutation create variation

• new muations are constantly apearing

mutation changes DNA sequence

How do mutations change DNA sequence

1. changes amino acid sequence

2. changes protein

3. changes structure

4. changes function

5. changes in protein may change phenotype and therefore change fitness

Describe gene flow

movement of individuals and alleles in and out of population

• seed and pollen distribution by wind and insects

• migration of animals

  • sub-populations may havae different allele frequencies

  • causes genetic mixing across regions

  • reduce differences between populations

Describe Non-Random mating

• Sexual selection

  • the probability that two individuals in a population will mate is not the same for all possible pairs of individuals

  • Mating is not random

Describe genetic drift (1. Founder effect)

• effect of chance events

• Founder effect

  • when a new population is started by only a few individuals

  • some rare alleles may be at a high frequency; others may be missing

  • skews the gene pool of new population

Describe genetic drift (2. Bottleneck)

• When large populations is drastically reduced by a disaster

  • famine, natural disaster, loss of habitat..

  • alleles lost from gene pool, not due to fitness

  • narros the gene pool

  • population recovers and expands again

example of an animal that experienced founder effect

darwins finches

example of an animal that suffered bottleneck and describe its impact

Cheetahs

• suffered a major bottleneck around 10,000 years ago

• all surviving cheetahs share their ancestry back to around a dozen or so indiviudals that survived

  • smaller gene pool, very similar genetically less than 1% diversity between cheetahs

• cheetahs now face another bottleneck from loss of habitat and poaching

Natural selection

differential survival and reproduction due to changing environmental conditions

• environment selects who is most fit and will reproduce

• combinations of alleles that provide “fitness” increase in the population

  • adaptive evolutionary change

5 Agents of evolutionary change

1. mutation

2. gene flow

3. non-random mating

4. genetic drift

5. selection

what is Hardy-Weinberg equilibrium

• a mathematical basis for population genetics

• based on a hypothetical, non-evolving population

  • acts as a model - null hypothesis

  • useful for measuring forces acting on populations

• Natural populations are rarely in the H-W equilibrium

what conditions would cause allele frequencies to not change?

for a hypothetical, non-evolving population.. remove all agents of evolutionary change

1. very large population size (no genetic drift)

2. no migration (no gene flow in or out)

3. no mutation (no genetic change)

4. random mating (no sexual selection)

5. no natural selection (everyone is equally fit)

Hardy-Weinberg equilibrium equation

p + q = 1

How do new species emerge

1. populations become isolated

   1. reproductive isolation

      1. sympatric speciation

   2. geographic isolation

      1. allopatric speciation

2. isolated populations evolve independently

what is allopatric speciation

• Geographic isolation

  • species occur in different areas

    • physical barriers like:

      • mountain range

      • canyon

      • river

      • division of a lake

What defines a specie

populations whose members can interbreed and produce viable fertile offspring

• must be reproductively compatible

Sympatric speciation

speciation occurs within the same geographic area

most common cause of sympatric speciation

a result of a meiotic failure during gamete formation

describe the failure of cytokinesis which causes meiotic failure during gamete formation

• chromosomal number will double in the gamete (diploid instead of haploid)

• offspring have additation sets of chromosome

  • polyploidy

• offspring may be viable and fertile

• but cannot interbreed with the original parent population

• speciation occurs

pre-zygotic meaning

beofre the zygote

what is meant by pre-reproduction barriers

• obstacles to mating or to fertilzation if mating occurs

• maintains reproductive isolation and prevent gene flow

what are the 6 pre-reproductive barriers

1. geographic isolation

2. ecological isolation

3. temporal isolation

4. behavioral isolation

5. mechnical isolation

6. gametic isolation

Ecological isolation

• species occur in same region, but occupy different habitats so rarely interbreed

Ecological isolation examples

• eg. lion and tigers could hybridize but they live in different habitats

  • lions in grasslands

  • tigers in rainforests

Temporal isolation

Species that breed during different times so gametes dont mix

• day, season, year

example: the american toad mates in the early part of summer, while the fowlers toad mates later in the season

Temporal isolation example

example: the american toad mates in the early part of summer, while the fowlers toad mates later in the season

Behavioral isolation

• unique behavioral patterns and rituals isolate species

  • identify members of species

  • attract mates of same species

    • courtship rituals, mating calls

• Should have same appearance and behaviours to attract

behavioral isolation example

ex: blue footed boobies mate only after a courtship display unique to their species

mechanical isolation

morphological (form/structure) differences can prevent successful mating

• for many insects, male and female sex organs of closely related species do not fit together, preventing sperm transfer

what are reasons why sperm of one specie may not be able to fertilize eggs of another

• Biochemical barrier

• chemical incompatibility

Biochemical barrier

sperm cannot penetrate egg

• receptor recognition: lock and key between egg and sperm

chemical incompatibility

sperm cannot survive in female reproductive tract

What is a Post-reproduction barrier

prevention of hybrid offspring from developing into a viable adult

what are the 3 post reproduction barriers

1. reduced hybrid viability

2. reduced hybrid fertility

3. hybrid breakdown

explain reduced hybrid viability

genes of different parent species may interact and impair the hybrids development

• might not reach reproductive age

• die early

explain reduced hybrid fertility

• even if hybrids are vigorous the maybe sterile

  • chromsomes of parents may differ in number or structure and meiosis in hybrids may fail to proudce normal gametes

explain hybrid breakdown

hybrids may be fertile and viable in first generation, but when they mate offspring are feeble or sterile

explain Gradualism in terms of rate of speciation

gradual divergence over long spans of time

• assume that big changes occur as the accumualation of many small ones

Explain punctuated equilibrium

rate of speciation is not constant

• rapid bursts of change

• long periods of little or no change

• species undergo rapid change when the 1st bud from parent pipulation

is evolution goal oriented?

NO, an evolutionary trend does NOT mean tha evolution is GOAL-ORIENTED

• evolution is not the survival of the fittest. Rather it is the survival of the just good enough

• surviving species do not represent the peak of perfect. there is compromise and random chance aswell

How do we know that organisms have changed over time? what do we look at (4)

1. Fossils

2. Anatomical

3. biogeographical

4. molecular

Describe fossil evidence

• Provide evidence of long-term evolutionary changes documenting the past existence of species that are now extinct

• Layers of sedimentary rock contain fossils

  • new layers cover older ones, creating records over time

  • fossils within layers show that a successsion of organisms have populated earth throughout a long period of time

Transition fossils