Evolution

The Origin of Life on Earth

Scientific hypothesis: testable, clear statement about what you think will happen based on prior knowledge

Scientific Theory: A scientific theory provides the most logical explanation for how or why something occurs in the natural world, supported by extensive evidence.

Scientific Law: Predicts the results of certain initial conditions, possible hair colour, what

1. The Early Earth

How long ago did the Earth form?

4.6 billion years ago

What was it like on the surface of early Earth?

Really hot 300 F, molten magma oceans, no O2 atmosphere, intense radiation, collision makes moon, volcanoes

How long ago did life evolve on Earth?

3.5 billion years ago

Where did life first appear on Earth and why this location?

Deep sea hydrothermal vents, chemical energy, nutrients, protection from surface conditions, warmth

What type of life forms (what kingdom) did the first life on Earth most resemble?

Archaebacteria, kingdom monera

2. Urey-Miller apparatus

Urey-Miller Apparatus and its contents.

Why was this experiment important?

First experimental evidence that life could have originated from non living matter-amino acids produced in 1 week. Opened door for prebiotic chemistry. Inspired testable science, simple molecules-> molecules of life. 

What was found when examining the sealed vials 55 years later? Does this support the

same conclusion as the original experiment?

Over 20 different amino acids + new ones from 1953 analysis, and greater quantities. Strengthened original conclusion, expanded on it, greater diversity of life building molecules could form. 

What further studies/experiments might you perform today to test the same hypothesis?

Stimulate other/more diverse earth Earth environments. Use updated atmosphere models (more CO2 N2, less methane-ammonia). Add minerals, stimulate natural surfaces, could be catalysts. Test for RNA formation. Ren long term self-evolving systems. 

3. Theories for origins of life on Earth

What is The Panspermia Theory?

A theory that proposes that life on Earth may have originated elsewhere in the universe and was transported to our planet through space. 

Does the Panspermia Theory explain the origin of life? Why or why not?

It doesn’t explain the origin of life itself, but it proposes a mechanism for its distribution across the universe. Building blocks of life were scattered in space and transported to Earth. 

How could the Panspermia Theory be tested?

Can be tested through a combination of experimental simulations (mimic space traveling to see if microorganisms could survive in space), search for evidence of extraterrestrial life, and analysis of planetary distribution effects. 

Describe some other scientific theories for how life appeared on Earth.

Primordial soup: Life originated from inorganic molecules which combine to form single organic molecules to the first cell.

Miller-Urey Experiment: Test that shows how simple organic molecules could be formed from inorganic compounds under early Earth conditions.

RNA World Hypothesis: Suggests that RNA was the primary genetic material in early life forms. RNA believed to be more flexible at carrying genetic info and act as enzyme.

Significant Events in History of Life

A little after 4000 my: first prokaryotic life forms appear

A little before 3000 my: prokaryotes with internal membranes

Between 3000 my and 2000 my: oxygen is abundant in atmosphere

A little before 1000 my: endosymbiotic life with mitochondria

1000 my: endosymbiotic life with chloroplasts

A little after 1000 my: multi-cellular life forms appear

A little after 600 my: shelled invertebrates

A little after 500 my: first vertebrates, jawless fish

A little before 400 my: plants invade land, arthropods invade land, jaws fish in sea

A little after 400 my: amphibians on land, trees and insects appear

A little before 300 my: reptiles appear

A little before 200 my: early dinosaurs

A little after 200 my: early mammals

A little after that: first birds

A little after 100 my: dinosaurs disappear

Right before 0.0: first primates

Early Ideas About Evolution

Darwin, Wallace, and Natural Selection

About Darwin:

• Well off

• Well educated

• Young, energetic

• Careful note taker - wasn’t good at star

• Lots of time to observe

HMS Beagle

• 5 year trip around the world

• Darwin wanted to go, he went as a gentlemen companion and then as a naturalist

• Stopped at many places in South America.

Noted pattern of life changing as he went south

• Found giant fossil species that resembled current  species there

Galapagos Islands

• Volcanic islands 1600 km from South America

• Very few land animals present; all of which arrived recently

• Each island had mocking birds with slightly different beaks and feeding habits

• Darwin’s Finches: each had different beaks & different diets

• The giant tortoises on each island had slightly different shells and ate slightly different plants.

Darwin in England

• Did more research on other collected specimens for 20 years, (1835-1855)

• Afraid of own theories & how they related to the church

Galapagos Finches

• Each island has unique finches

• Finches beaks match their diets

• Mainland only has one finch

• Darwin thought that diet may have influenced (helped select/shape) the beaks of the finches

About Wallace

• Not well off

• Sold specimens he collected, birds of paradise, collected birds for Darwin

• Careful observer, better than Darwin

• Visited islands

Wallace’s Observations

• The plants did not change from Java -> Bali -> Lombok

• Sailing 1000 km from Java to Bali, saw only hornbills eating large fruit with big seeds

• After crossing 32km of ocean, at Lombok, saw only cockatoos eating same large fruit with same big seeds

• Wallace wondered: why had God had created two such different birds to eat the same large fruit on two islands that were right beside each other?

Wallace Concluded:

• The environment  had selected the best Asian bird [the hornbill] and the best Australian bird [the cockatoo] to match the same fruit

Darwin/ Wallace Each concluded:

• Environment somehow shaped species

• species vary due to Natural selection

Natural Selection

Darwin & Wallace influenced by:  Malthus – Essay on Population

Key idea: more births occur than can be supported so only the ‘fit’ survive

Wallace Wrote Darwin

• They shared similar theories

• Darwin was afraid Wallace would scoop (go public and get credit) him

• Darwin’s friends manipulated Wallace to publish a joint paper 1858

Darwin published: in 1859

“On the Origin of Species, by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.”

Critical Elements of Darwin’s Theory

Variations:

• Individual members of a species vary in physical characteristics

• Physical variations can be passed from generations

Struggle for Existence:

• The members of all species compete with each other for limited resources

• Certain members are able to capture these resources better than the others

Survival of the Fittest:

• Certain members of the population are selected to produce more offspring simply because

they happen to have a variation that makes them better suited to the environment

Adaptation

• Natural selection causes a population of organisms and ultimately a species to become

adapted to the environment

• The process is slow, but each subsequent generation includes more individuals that

are better adapted to the environment

Natural Selection and Evolution

What assumptions did Darwin make?

Offspring vary-some of variation is inheritable. More offspring are born that can survive-populations are stable don’t generally increase

What inferences did Darwin make?

Individuals of the same species will compete. Survivors pass on favourable traits to the population overtime, more traits from survivors. 

These inferences led to his theory of evolution by natural selection.

Explain the following examples of Natural Selection

• a leaf-like praying mantis-camouflage

• peppered moths in pre- and post-industrial England-different camouflage

• mimicry of the poisonous coral snake by the non-poisonous king snake-scares others for safety

Compare Homologous, Analogous, and Vestigial Features

• Homologous structures: Similar structures with very different functions. Examples: wings, arms, flippers

• Analogous structures: Different structures, similar functions

• Vestigial structures: No function in one organism, have a function in similar organisms. 

Macroevolution vs. Microevolution

Macroevolution

• Large scale evolutionary change significant enough to warrant the classification of groups or

lineages into distinct genera or even higher-level taxa-common ancestors

E.g. long time (10,000 to millions of years), Darwins finches

Microevolution:

• Changes in gene (allele) frequencies and phenotypic traits within populations and species; can

result in the formation of new species

E.g. less time (10s to 1000s of years), antibiotic resistance in bacteria

Evidence for Evolution

1. The Fossil Record

• Evidence of variety of life

• Evidence of extinct species

• Evidence of transitional species (e.g. Basilosaurus was a relative of a modern whale with hind limbs and Archaeopteryx shows a transition between reptiles and birds)

What are fossils? Any preserved remains of an organism or its activity (body fossils, casts, molds, footprints, feeding traces)

How does fossilization occur? Lithification, copy, as sediments become compressed by the weight of overlying sediments they slowly undergo lithification turn into stone (lithification)

What are some types of fossils?

Encrustation: Sediment on outside

Tar impregnation: Animals got stuck in tar

Amber entombment: Trapped in resin or sap from tree

Refrigeration: Frozen ice age, babies

Mummification: Dried out

Petrified wood

Molds/Tracks

Burrows: Invertebrates where they were

Gastroliths: Stones eaten by birds and dinosaurs

Coprolites: Fossilized pooped

How do we know how old they are?

Radiometric dating, radio-isotopes

2. Chemical and Anatomical Similarities

• Cellular structure is common to all living things

• Proteins, carbohydrates, lipids, and nucleic acids are common to all living things

• Genetic code is the same for all living things

• Groups of species share common body structures

• e.g. homologous structures: common origin, different functions, (human arm, cat leg, whale flippers, bat hands) 

•  e.g. analogous structures: different structure, same function, unrelated species, (shark fin, penguin wing, dolphin flippers), (bird wing, bat wing, insect wings), (kangaroos knee, human knee)

• e.g. vestigial structures: non functioning, have a necessary function in ancestors or relatives (human appendix, koala appendix, gorilla appendix), (whale pelvis, ancient amphibians), (ostrich wings), (goosebumps)

• e.g. anatomical oddities: suggestive of evolutionary past, no current need, (laryngeal nerve-down neck under heart, to larynx, from fix heart on way to larynx/gills)

• e.g. similarities between vertebrate embryos

3. Geographic Distribution of Related Species

• Isolated lands and islands have evolved distinct plants and animals (e.g. Australia and Hawaii)

Why? Less interactions, ancestors split off a while ago

• Biogeography: the scientific study of the geographic distribution of organisms based on both living

species and fossils

4. Genetic Changes are Observed Over Generations

• Organisms that mature and reproduce quickly evolve quickly

• E.g. mutations in bacteria lead to antibiotic resistance, pesticide resistant insects

• An increase in the number of genes = the potential form more diversity

• An increase in the number of alleles = more variation in species

• Sexual reproduction results in increased genetic diversity

• E.g. a bacterium has 470 genes; a fruit fly has 13,000 genes, a human has roughly 42,000

5. Artificial Selection/Selective Breeding

• Humans breed plants or animals to develop particular phenotypes by choosing mating partners

• E.g. fancy pigeons, chickens-agriculture, fruits, carrots-stopped breeding other colours

Types of Selection

1. Stabilizing Selection

• Most common form of selection

• The extreme values for a trait are selected against

•  Over time, the population mean stays the same and the range decreases

  • E.g. hummingbird beak length-most successful birds will have beaks thatsuit flowers in their environment, coelacanths, horseshoe crabs

2. Directional Selection

• Selection favours one of the extremes

• Over time, the population mean shifts up or down over time

  • E.g. hummingbirds move to new location with longer flowers longer beaks favoured, peppered moths, salmon in BC

3. Disruptive Selection

• Selection favours both of the extremes in a population; 2 populations result with altered means and reduced ranges

• These 2 populations may become isolated breeding populations and new species

  • E.g. hummingbird feeds on 2 types of flowers (short, long) short and long beaks are both selected, african swallowtail butterfly

4. Sexual Selection

• The selection of any trait that influences the mating success of an individual

• Traits that are favoured tend to be sexual dimorphic (male and females with very different physical appearances)

• Female choice is based on colouration, courtship displays, etc.

  • E.g. peacock feathers, crane dances

• Male/male competition, e.g. strength to fight other males or defend territory

  • E.g. claws and teeth fights baboon, turtles flip each other

5. Cumulative Selection

• The accumulation of many small evolutionary changes over long periods of time and many generations

• Results in significant new adaptations relative to the ancestral species

• E.g. evolution of the eye, evolution of pollination

6. Altruism

• Behaviour that decreases the fitness of an individual that is assisting or cooperating with a recipient individual whose fitness is increased

• Kin selection: the natural selection of a behaviour or trait of one individual that enhances the success of closely related individuals, thereby increasing the first individuals fitness indirectly

  • E.g. primates, elephants, bees

Random Change in a Population

 Evolution happens with populations, NOT individuals

We say that a population has evolved when it is different from the original population in its genetic

makeup.

1. a) Genetic Drift

• Inn small populations, alleles can be lost at random from the population

• For example: 2 populations with an allele frequency of 1%, small the allele will live close, large will live spread out. If a random event kills 1% of the population it is unlikely that all will be killed in a large, but in a small it is more likely. 

• Genetic drift can result in dramatic change in a small population, but in a large population is not usually significant.

• Genetic drift affects the genetic makeup of a population, but unlike natural selection, through an entirely random process.

• Genetic drift is a mechanism of evolution, it doesn’t work to produce adaptations.

1. b) Bottleneck Effect

• This is a large, usually temporary, reduction in the population that may result in significant genetic drift

• For Example: Elephant seals, cheetahs, 100,000 sels-> 20 in 1890s->30,000 lost diversity

• Near extinction event

1. c) The Founder Effect

• This results when a small population colonizes a new area, causing a limited number of alleles to be present which is a form of genetic drift

• For Example: Iguanas arriving on Caribbean island trapped in 1995. Pennsylvania Amish started with 30 people, 1 had extra finger, became much more common there than in the greater population

2. Gene Flow

• Often animals live in isolated colonies

• Sometimes males or females are driven out of the home colony and move to a new colony

• These individuals bring their alleles with them and will likely alter the genetic balance in the new colony

  • E.g. prairie dogs, elephants, primates

  • Gene flow reduces differences between populations while genetic drift increases differences between populations

Why? To prevent breeding problems and incest

3. Mutations

• Neutral mutations usually occur in noncoding regions of genetic material but can provide additional genetic material

• Beneficial  mutations are rare but the environment selects them and, therefore, alleles resulting from them accumulate over time

• Harmful mutations occur frequently but the environment selects against them and, therefore, alleles that result from them are rare

• While rare in individual cells, mutations are numerous in large amounts over many generations

  • E.g. sickle cell anemia: weird shaped Red blood cell, can’t carry O2 well, immune from malaria

Speciation

1. Reproductive Isolating Mechanisms

• In order for one population to become very different from another, they must be reproductively isolated.

• This means that there will no longer be a free exchange of alleles between two populations. 

• Prezygotic mechanisms prevent mating or fertilization

• Postzygotic mechanisms prevent the development of fertile offspring

1A. Prezygotic Mechanisms

A. Ecololgical Isolation

• Two populations are in different geographical places or in different places within the same ecosystem

• E.g. bengal tiger lives in forest and Asiatic lion lives on savannah. Woodchuck in fields marmot in alpine meadows

B. Temporal Isolation

• Two populations are unable to exchange alleles because they are available to exchange alleles at different times of the year or day

• E.g. Cactus blooms at sunset, morning glory at sunrise. Goldfinch mates in August and purple finches in June due to availability in food. 

C. Behavioural Isolation

• Two populations do not respond to each others mating rituals

• E.g. Male black crickets and grey crickets rub their legs together at different frequencies

D. Mechanical Isolation

• A physical barrier that prevents fertilization or mating

• E.g. Insect exoskeletons allow for male/female lock & key fit. Orchid shape specific insect pollinators

E. Gametic Isolation

• Two populations exchange sperm and eggs but chemical markers prevent the eggs from being fertilized by the ‘wrong’ sperm

• E.g. Wind blown pollen from corn will not travel through the stigma of the milkweed. Clam sperm will not fertilize fish eggs due to incorrect enzymes

1B. Postzygotic Mechanisms

A. Zygotic mortality

• Even though zygote is created, it fails to develop to maturity

• E.g. Dies before mom knows pregnant

B. Hybrid inviability

• Even though the hybrid is born, it does not live long or is not healthy

• E.g. died after birth

C. Hybrid Infertility

• Even though hybrid is healthy and vigorous, it is not able to reproduce

• Donkey + Horse = mule, mule = infertile

2. Speciation

• When two populations become completely isolated and no longer exchange alleles, they are said

to have formed separate species.

A. Allopatric Speciation

• Two populations are geographically isolated prior to becoming separate species

• E.g. Fish separated by a dam

B. Sympatric Speciation

• Two populations remain in physical contact with each other but still stop exchanging alleles and become separate species

• Stickleback fish occupying different habitats in the same lake

3. Divergent and Convergent Evolution

1. Divergent Evolution

• Results from two or more species evolving increasingly different traits as a result of different selective pressures or genetic drift

• E.g. house cats vs wild cats

2. Convergent Evolution

• Results from two unrelated species being subjected to similar selective pressures which result in similar phenotypes

• E.g. sharks vs dolphins, similar body shape and finds. Placental mammals (everywhere), marsupials (Australia)

4. Coevolution

• One species evolves in response to the evolution of another species

• E.g. plants hard shells to protect seeds, seed-eating mammals evolved powerful jaws. Madagascar long spurred and hawk moth

5. Adaptive Radiation

• A single species evolves into a number of distinct but closely related species

• Each new species fills a different ecological niche

• Occurs because a new variety of resources becomes valuable (not yet being used by other species)

• E.g. Darwin's finches, marsupial Australia ancestor

Hardy‐Weinberg Principle

Measuring Changes in Allele Frequencies

Evolution is defined as the change in allele frequency of a population over time. Therefore, if we examine the frequencies of alleles using the genotypes in populations, we can determine if a population is undergoing microevolution. Changes in these frequencies indicate changes in genetic which is a measure of microevolution

How do we measure alleles and genotypes?

Let’s use mice as an example: they have two alleles for fur colour:

Dominant B allele for: black fur, Recessive b allele for: white fur

Mice genotypes can be:

Let’s assume that in a population of 400 mice: 207 area BB, 146 are Bb, 47 are bb.

Calculate the genotype frequencies:

BB/total =207/400 = 0.52 homozygous dominant

Bb/total =140/400 =.36 heterozygous

bb/total = 47/400= .12 homozygous recessive

What do you notice about the sum of genotype frequencies? Add up to 1

Now calculate the allele frequency in the population:

Each mouse in the population has 2 alleles for fur colour so there are:

➢ 400 x 2=800 alleles in the population

Let’s determine the Frequency of B allele:

Each BB gives 2 B allele: 207 x 2 = 414 B alleles

Each Bb gives 1 B allele: 146 x 1= 146 B allele

146 + 414 = 560 B alleles in population, frequency of B is 500/800 = .7

Let’s determine the Frequency of b allele:

Each Bb gives 1 b allele: 146 x 1 = 146

Each bb gives 2 b alleles: 47 x 2 = 94

146 + 94 = 240 b alleles in population, frequency of b is 240/800 = .3

Notice that frequency of B allele + frequency of b allele = 1

So how does this measure evolution?

If all members of a population were genetically identical they would produce identical offspring and there

would be no change in the population (no evolution). If there is a change in allele and genotype frequencies over many generations, then microevolution is said to occur. 

So, let’s sample our mice population five years later. This time we find 600 mice : 210 are BB, 112 are Bb and 278 are bb

Genotype frequencies:

BB/total = 210/600 = .35 homozygous dominant

Bb/total = 112/600 = .19 heterozygous

bb/total = 278/600 = .46 homozygous recessive

Compare these genotype frequencies to the first data set: they are significantly different form the first data set

Allele frequencies:

Dominant B allele: p

BB - 210 x 2 =420

Bb - 112 x 1 = 112

420 + 112 / 2 x 600 = 532/1200 = .44

p = .44

Recessive b allele: q

bb - 2 x 278 = 556

Bb - 112 x 1 = 112

556 + 112 / 2 x 600 = 668/1200 = .56

q=.56

Now compare the allele frequencies to the first data set....are they the same or different: they are significantly different 

Has microevolution occurred? Yes

Hardy‐Weinberg Principle

This principle specifies the conditions under which there would be NO change in the genotype and allele

frequencies from generation to generation. This means no evolution!

Hardy Weinberg Principles:

1. Large population size

2. Random mating: females can't select male based on a particular genotype or vice versa, male vs male selection

3. No mutations: alleles in gene pool cannot change

4. No gene flow: no exchange of genes between populations, no migrations, very isolated

5. No natural selection: no genotype can have a reproductive advantage over another

When all these conditions are met, the genotype and allele frequencies do not change and the population is

said to be in Hardy‐Weinberg equilibrium

In real life, none of those conditions are completely satisfied and there is always some fluctuations in allele

frequencies.

Hardy Weinberg Equations:

p+q = 1 p2 + 2pq + p2 = 1

Human Evolution

What makes humans unique?

1. Ability to perform complex reasoning

2. Strong ability to learn

3. Sophisticated tools

4. Communicate using complex language

5. Large brain relative to body size

6. Hands capable of fine manipulation and coordination

7. Bipedalism

Are these 7 traits truly unique to us?

No

Hominid Evolution

• Bipedalism evolved 6 to 7 million years ago.

• First use of stonetools 3.4 million years ago by Australopithecus.

• Genus Homo evolved 2 million years ago.

• Fire was first used for cooking 1.5 million years ago.

• Modern Humans evolved about 230 000 years ago.

This map shows: Human migration

This Cladogram shows: Human ancestors 

What physical characteristics of hominids changed over time? How did they change?

Brain size: Increased

Diet and size of chewing muscles

Pelvis: Bipedalism, and babies with big heads

Feet: Longer toes, legs with broader heel for running