evolution unit review

Microevolution

is change in the frequency of a gene pool on a small scale

Happens from one generation to the next

Gene Flow (migration)

Description: Gene flow is the movement of alleles between two interbreeding populations with different allele frequencies.

Effect: It changes allele frequencies in one or both populations as genes move between them.

Example: Prairie dog colonies are normally closed, but in summer mature males can enter new colonies, introducing new genes and altering the gene pool.

Non-random Mating

Description: During non-random mating, individuals in a population select mates, often on the basis of their phenotypes.

Effect: Non-random mating increases the proportion of homozygous individuals in a population.

GENETIC DRIFT

Description: random change in genetic variation from generation to generation due to chance.

Effect: Genetic drift changes allele frequencies

GENETIC DRIFT: THE BOTTLENECK EFFECT

When a severe event results in a drastic reduction in numbers, a population may experience a bottleneck effect.

A very small sample of alleles survives to establish a new population.

GENETIC DRIFT: THE FOUNDER EFFECT

When a few individuals from a large population leave to establish a new population

1. SEXUAL SELECTION

Favours the selection of any trait that influences the mating success of the individual.

Process by which individuals compete for the chance for a mate.

2. Stabilizing selection

It favors the intermediate variants.

Stabilizing selection tends to remove the more severe phenotypes, resulting in the reproductive success of the norm or average phenotypes.

3. Directional selection

is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes.

4. Disruptive selection

Describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases, and the population is divided into two distinct groups.

Macroevolution

is evolution over geologic time of groups larger than just an individual.

The process by which a new species evolves is called speciation.

Biological Species Concept

A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring.

**Breeding behavior in nature can be different than in captivity (artifical enviornemtn)

How do new species arise?

some members of a species must become reproductively isolated from the rest of the species.

- Evolution within a species means a change in that population’s allele frequency.

When two populations are separated, their allele frequency changes separately from one another.

Since they no longer have migration between the populations, two separate species may develop.

**There are many ways to separate two populations.

Allopatric Speciation

Happens when a geographical barrier (mountains, rivers, oceans, distance) splits a population into two groups.

After being separated, each group develops differences that eventually prevent them from interbreeding.

“Allo” means other/different and “patric” means from → “from different places.”

Geographical isolation is the main cause that starts this type of speciation.

Over time, physical, behavioural, or genetic changes build up and keep the two groups reproductively isolated (unable to mate).

Example

A river forms and splits a population of squirrels.

Each group adapts to its side of the river.

Over many generations, their behaviours and traits change so much that even if they meet again, they no longer mate → they have become two different species.

Reproductive Isolation (formed by geographic isolation)

Any factor in nature that prevents interbreeding (breeding within a closed population) between individuals of the same or closely related species.

Extrinsic isolating mechanism – outside of the organisms in question

Geographic isolation is extrinsic

• Geographic isolation: mountains, rivers, oceans, or distance physically separate populations.

• Habitat isolation: one group lives in trees, another on the ground.

• Temporal isolation (if caused by climate/seasonal differences): they breed at different times because environments differ.

Intrinsic isolating mechanism – internal characteristics that prevent interbreeding

Differences in anatomy, physiology and behavior

Types of Intrinsic Reproductive Isolating Mechanisms

Ecological

Temporal

Behavioral

Mechanical

Gametic

Hybrid inviability

1. Ecological Isolation

A premating (prezygotic) isolating mechanism in which members of different species seldom, if ever, meet because each species prefers to live (is adapted to) different habitats.

(Two species don’t mate because they live in different places, so they never meet.)

When two species have different habitats, they will rarely have contact.

Lions prefer open grassland, tigers prefer forest

2. Temporal Isolation (time-based isolation)

Two or more species that share the same habitat but do not mate within the same time frame.

Two populations of the same species of plant release their pollen at different times of the year. If their reproductive periods did not overlap, they would have reduced gene flow.

Their reproductive periods don't overlap → they barely exchange genes → reduced gene flow.

3. Behavioral Isolation

Even if populations are in contact and breeding can occur, they must choose to mate.

Such a choice is based on specific courtship and mating displays.

4. Mechanical Isolation

Type of prezygotic isolation where reproductive organs differ in size or shape or another feature.

Different species of Alpine Butterfly look similar but have different reproductive organs.

5. Gametic Isolation

Even if mating occurs, offspring may not result if there are incompatibilities between sperm and egg, or between sperm and the female reproductive tract.

6. Hybrid Inviability or Infertility

Hybrids between closely related species are often inviable or, if they live, they are sterile.

This hybrid inviability and sterility, (hybrid incompatibility), can reduce the exchange of genetic variants between species.

Even if offspring develop, they are most often malformed or sterile

Sympatric Speciation

Sympatric speciation occurs when there are no physical barriers preventing any members of a species from mating with another, and all members are in close proximity to one another.

Even though they’re in the same place, a new species can still form if some individuals start using a different resource (like a new food) or develop a new trait that separates them reproductively.

In plants, this often happens through polyploidy, which is when the number of chromosome sets doubles or changes. Polyploid individuals can’t successfully mate with the original population, so they form a new species.s

Polyploidy

100,000 species of plants exist today because of polyploidy

A multiplication of the normal number of chromosomes in an organism.

Most often happens in plants that self pollinate

When does speciation occur?

Consider the horseshoe crab which has not changed much in 300 million years.

Consider Darwin’s finches, they developed into 13 separate species in 100,000 years.

Horseshoe crabs didn’t face strong pressures, so speciation was minimal.

Darwin’s finches faced different pressures on different islands, so speciation was fast.

Generalists' vs Specialists

The horseshoe crabs are generalists – their diet is diverse

The finches are specialists – their diet is very specific, especially when food is scarce.

When the food source changes, the finches must adapt, or they will not survive. The horseshoe crab just moves on and eats something else.

Adaptive Radiation

Rapid emergence of species from a single species that has been introduced into a new environment.

ex. When the finches arrived on the Galapagos there were no other birds of their kind living in the islands.

It was easy for them to specialize and fill the available niches. This is especially true on the Galapagos because there are 25 separate islands.

Water between the islands is a barrier = allopatric speciation

Two conditions that contribute to speciation

Specialization of food source and environment

Ability to migrate to a new environment, especially if there is no competition.

Convergent vs Divergent Evolution

Convergent evolution occurs when species have different ancestral origins but have developed similar features.

Divergent evolution occurs when two separate species evolve differently from a common ancestor

1. evidence for evolution

Anatomy

Homologous Structures

• Same structure + origin

• Different function

• Show divergent evolution (common ancestor) Divergent evolution happens when one species splits into multiple species because they adapt to different environments.

Analogous Structures

• Same function

• Different origin/structure

• Show convergent evolution (similar environments)

Vestigial Structures

• Leftover structures from ancestors

• No current function

• Evidence of evolutionary change

2. evidence for evolution

2. Biogeography

Island Populations

• Species evolve differently when isolated

• Limited gene flow → unique traits

Coastlines of Continents

Continents fit together (e.g., Gondwana)

Similar fossils found on far-apart coasts

3 evidence for evolution

3. Fossils

Chronological Order

Fossils appear in predictable layers (oldest at bottom)

Transitional Fossils

Show intermediate stages between groups

Example: Archaeopteryx (between dinosaurs & birds)

Vestigial Structures in Fossils

Show structure changes over time

Dating Fossils

Carbon-14 dating (recent)

Uranium dating (older)

Other radiometric methods

Examples from Class

Burgess Shale (amazing fossil preservation)

Darwin finding seashells in mountains (land once underwater)

4 evidence for evolution

4. Embryology

Similar embryonic stages across species

Too similar to be by chance → evidence of common ancestry

5 evidence for evolution

5. DNA

Comparing DNA shows how closely related species are

Traits passed through generations

Mutations create variation over time

 Class Examples (Fish)

Red Grouper

Iridescent Shark

Escolar

Albacore Tuna

(compare anatomy, DNA, or diets)

6 evidence for evolution

Evolutionary Patterns

Divergent Evolution

Same species → isolated into different environments

Limited gene flow

Different traits selected

Homologous structures

Convergent Evolution

Not closely related

Evolve similar traits due to similar environments

Analogous structures

Parallel Evolution

Two related species

Independently evolve in similar ways

Voyage of Beagle

Dates: February 12th, 1831

Captain: Robert FitzRoy

Ship: H.M.S. Beagle

Destination: Voyage around the world.

Findings: evidence to propose a revolutionary hypothesis about how life changes over time

Fun fact: Charles Darwin was to go into medicine but changed his mind and joined this voyage instead. He did not even get along with the captain and they had many disputes.

Patterns of Diversity

Darwin visited Argentina and Australia which had similar grassland ecosystems.

those grasslands were inhabited by very different animals.

neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.

Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them?

Why were there no kangaroos in England?

Living Organisms and Fossils

Darwin collected the preserved remains of ancient organisms, called fossils.

Some of those fossils resembled organisms that were still alive today.

Others looked completely unlike any creature he had ever seen.

As Darwin studied fossils, new questions arose.

Why had so many of these species disappeared?

How were they related to living species?

The Galapagos Island

The lowest islands, like Hood Island, were hot, dry, and nearly barren with sparse vegetation. (Almost nothing grows there)

Higher islands, like Isabela Island, had more rainfall and rich vegetation.

Darwin was fascinated by the tortoises and marine iguanas.

Giant tortoises varied from island to island, and the shape of their shells showed which island they came from.

Animals found in the Galapagos

Land Tortoises

Darwin Finches

Blue-Footed Booby

Marine Iguanas

The Journey Home

Darwin Observed that characteristics of many plants and animals vary greatly among the islands

Hypothesis: Separate species may have arisen from an original ancestor

Ideas that shaped Darwin’s Thinking

James Hutton:

1795 Theory of Geological change

Forces change earth’s surface shape

Changes are slow

Earth much older than thousands of years

Charles Lyell

Book: Principles of Geography

Geographical features can be built up or torn down

Darwin thought if earth changed over time, what about life?

Lamarck

Tendency toward Perfection(Giraffe necks)

Use and Disuse (bird’s using forearms)

Inheritance of Acquired Traits

Thomas Malthus-19th century English economist

If population grew (more Babies born than die)

Insufficient living space

Food runs out

Darwin applied this theory to animals

Publication of Orgin of Species

Russel Wallace wrote an essay summarizing evolutionary change from his field work in Malaysia

Gave Darwin the drive to publish his findings

Darwin`s Birds

Darwin observed many birds and noticed they had some similarities and differences.

Ornithologist John Gould informed Darwin that 25 of his 26 Galapagos birds were different species.

Darwin did not label them by island during his collections but this evidence suggests that there is a single ancestral species transported from a nearby land.

Other Species

Darwin notes the islands were inhabited by many bird species and species that were able to swim and sustain long periods of time at sea such as land lizards and turtles.

Mammals that were unable to survive such travel were not present on the islands. (except rats and domestic animals from ships)

Species had traveled to these islands and evolved and adapted to suit the conditions.

Homologous Features

Homologous – structures that share a common origin but may serve different functions in modern species.

Example – dolphin flippers and human hands

Analogous Features

Features that are shared by many organisms and serving a common function

Ex. Wings of birds, butterflies

Darwin came to the conclusion that organisms with homologous features likely shared a more recent common ancestor, while those with analogous features did not.

Vestigial Features

Structures that serve no purpose in living organisms. Example digits in dogs, pigs and whales

Artificial Selection

Artificial selection is intentional breeding for certain traits, where human influence shapes a species’ evolution.

Darwin saw that species have inherited variations that can be selected for desirable changes.

Artificial selection helped him understand how evolution could work in nature.

Favourable traits are preserved; unfavourable ones are eliminated.

Seven years after his voyage, Darwin concluded that species evolve through natural selection—traits become more or less common depending on survival and reproduction.

Wallace proposed the same idea, prompting Darwin to publish his findings first.

Natural Selection (VISTA)

A simple mechanism explains how populations change over time.

Variation:

Individuals of a species differ due to random mutations.

Inheritance:

Organisms pass on their DNA — including new mutations — to their offspring.

Selection:

Because resources are limited, not all individuals survive; those better at finding food, avoiding predators, or mating are more likely to thrive.

Time:

Across generations, advantageous traits get passed on to more offspring.

Adaptation:

Over many generations, these traits become common, producing a population better suited to its environment.

Problems with Darwin’s work

Some criticized Darwin because he could offer no explanation for the source of new variations.

6 years later Gregor Mendel proposed his theories for genetic variations.

1. How is genetic variation acquired?

Genetic variation is acquired through:

• Mutations — random changes in DNA.

• Meiosis (sexual reproduction) — mixing of genes through crossing over and independent assortment.

• Fertilization — combining DNA from two parents to create unique offspring.

• Gene flow — new genes entering a population when individuals migrate.

Mimicry

The ability to mimic something that they are not

Ex. Many harmless species resemble a harmful species in colouration or structure. Predators that avoid that species will also avoid the mimic.

Development of Adaptations

Adaptations come from gradual, helpful changes caused by random DNA mutations over many generations.

Variations are structural, functional, or physiological differences within a species.

Not all variations become adaptations — it depends on the environment.

Helpful variations boost survival and reproduction, so they get passed on and become more common.

Over time, these beneficial traits become adaptations.

Some traits aren’t useful at first but can become helpful if the environment changes.

Example: Peppered moth — the dark form became favoured during industrial pollution.

What Leads to Genetic Variation?

MUTATIONS – are changes in the genetic material

Can occur spontaneously altering the alleles in an individual

May cause a new characteristic that can be beneficial to a species

Selective Advantage

Mutations that were neutral or harmful can become helpful if the environment changes.

Helpful mutations give organisms a selective advantage — they survive and reproduce better.

Examples:

Daphnia with mutations that let them survive wider temperature ranges

Bacteria where a single mutation can spread quickly and cause antibiotic resistance

Homologous Structures → Divergent Evolution

2. Analogous Structures → Convergent Evolution

1. Homologous Structures → Divergent Evolution

Homologous = same origin, different function.

Examples: human arm, cat leg, whale flipper, bat wing.

Why this means divergent evolution:

All these structures come from a common ancestor.

Over time, that ancestor’s descendants moved into different environments.

Because the environments and uses were different, the structure diverged (changed in different directions).

Same starting blueprint → modified for different purposes.

Visual logic:

Common ancestor → branches out → different forms

This is divergence.

Key idea:

Homologous structures show shared ancestry, so they prove divergent evolution.

2. Analogous Structures → Convergent Evolution

Analogous = different origin, same function.

Examples: butterfly wing vs bird wing, shark fin vs dolphin flipper.

Why this means convergent evolution:

These organisms do not share a recent common ancestor with that structure.

They live in similar environments or face similar selective pressures.

Because of this, they independently develop similar solutions to the same problem.

Different starting blueprints → evolve to look/function similarly.

Different ancestors → converge → similar function

This is convergence.

Key idea:

Analogous structures show similar adaptations without shared ancestry, so they prove convergent evolution.