Evolution Part 1: Evolution Part 1: Natural SelectionNatural Selection

 

 

Charles DarwinCharles Darwin1809-18821809-1882

•The Father of EvolutionThe Father of Evolution

•Born in 1809, EnglandBorn in 1809, England

•Sailed on the Sailed on the HMS BeagleHMS Beagle

•During his voyage, he madeDuring his voyage, he madeobservations that ledobservations that ledhim to his theory of him to his theory of evolutionevolution

This voyage lasted fromThis voyage lasted from 1831 1831 toto 1836. 1836. This voyage lasted fromThis voyage lasted from 1831 1831 toto 1836. 1836.

The Galapagos The Galapagos Islands lie 500 miles Islands lie 500 miles west of Ecuador in west of Ecuador in the Pacific Ocean, the Pacific Ocean,

directly on the directly on the equator.equator.

The Galapagos The Galapagos Islands lie 500 miles Islands lie 500 miles west of Ecuador in west of Ecuador in the Pacific Ocean, the Pacific Ocean,

directly on the directly on the equator.equator.

Many of Darwin’s Many of Darwin’s conclusions were conclusions were

based on based on observations of observations of

wildlife in thewildlife in the Galapagos IslandsGalapagos Islands..

Many of Darwin’s Many of Darwin’s conclusions were conclusions were

based on based on observations of observations of

wildlife in thewildlife in the Galapagos IslandsGalapagos Islands..

“Galapagos” means turtle.

Among other Among other things, Darwin things, Darwin

noticed there were noticed there were several types of several types of finches on these finches on these

islands.islands.

Among other Among other things, Darwin things, Darwin

noticed there were noticed there were several types of several types of finches on these finches on these

islands.islands.

In particular, In particular, Darwin observed Darwin observed something odd something odd

about the about the finches: they all finches: they all

looked like a looked like a bird he had seen bird he had seen

on theon the South South American American continent.continent.

In particular, In particular, Darwin observed Darwin observed something odd something odd

about the about the finches: they all finches: they all

looked like a looked like a bird he had seen bird he had seen

on theon the South South American American continent.continent.

The most distinct difference among finch The most distinct difference among finch species is theirspecies is their beaks, beaks, which are adapted for which are adapted for

the specific diets available on the islands.the specific diets available on the islands.

The most distinct difference among finch The most distinct difference among finch species is theirspecies is their beaks, beaks, which are adapted for which are adapted for

the specific diets available on the islands.the specific diets available on the islands.

Darwin Darwin hypothesized that hypothesized that some of the birds some of the birds

from South America from South America migrated to the migrated to the

Galapagos.Galapagos.

Darwin Darwin hypothesized that hypothesized that some of the birds some of the birds

from South America from South America migrated to the migrated to the

Galapagos.Galapagos.

Once on the islands, Once on the islands, the birds must have the birds must have

changed changed over the over the years.years.

Once on the islands, Once on the islands, the birds must have the birds must have

changed changed over the over the years.years.

This would explain the numerous species of This would explain the numerous species of birds present.birds present.

This would explain the numerous species of This would explain the numerous species of birds present.birds present.

Warbler Finch

Tree Finch

Ground Finch

Certhidea olivacea

& C. Fusca

Geospiza difficilisG. conirostris

G. scandens Cacts Finch(nectar,eeds, blood)

G. magnirostris

Seed-eating Finch

G. fuliginosa

G. fortis

Platyspiza crassitrostris

C. heliobates

Cactospiza pallida

Woodpecker-like Finch

Vegetarian Finch

Insect-eating Finch

Camarhynchus pauper

C. psittacula

C. pauper

(seeds & insects)

PHYLOGENETIC TREE:A diagram showing the evolutionary history of a species of an animal.

The common ancestor is at the bottom.

This tree has how many major branches?

“Original” Finch

Darwin called the mechanism Darwin called the mechanism for evolution…for evolution…

Darwin called the mechanism Darwin called the mechanism for evolution…for evolution…

Darwin called this…Darwin called this…which means change in species over timewhich means change in species over time

After returning from the Galapagos and studying all After returning from the Galapagos and studying all the different types of plants & animals he collected the different types of plants & animals he collected during the voyage, Darwin concluded that during the voyage, Darwin concluded that organisms change over time….organisms change over time….

a.k.a.a.k.a. Survival of the Fittest. Survival of the Fittest.

Those individuals that are better fit for their Those individuals that are better fit for their environment have a greater chance to environment have a greater chance to survive and mate. Therefore, their genetic survive and mate. Therefore, their genetic traits become more common or frequent traits become more common or frequent over time. The genetic traits of less fit over time. The genetic traits of less fit individuals become less common or individuals become less common or frequent over time.frequent over time.

a.k.a.a.k.a. Survival of the Fittest. Survival of the Fittest.

Those individuals that are better fit for their Those individuals that are better fit for their environment have a greater chance to environment have a greater chance to survive and mate. Therefore, their genetic survive and mate. Therefore, their genetic traits become more common or frequent traits become more common or frequent over time. The genetic traits of less fit over time. The genetic traits of less fit individuals become less common or individuals become less common or frequent over time.frequent over time.

The recipe forThe recipe forThe recipe forThe recipe for

1. All species have genetic variation.1. All species have genetic variation.1. All species have genetic variation.1. All species have genetic variation.

Every species is different, Every species is different, even within itself.even within itself.

Every species is different, Every species is different, even within itself.even within itself.

Example:Example:some beetles (of the some beetles (of the same species) are green same species) are green and some are brown and some are brown

http://evolution.berkeley.edu/evolibrary/

There is a constant There is a constant struggle for survival. struggle for survival.

Examples are:Examples are: Natural disasters like Natural disasters like droughts, fires, floods, etc.droughts, fires, floods, etc.

Competition for resources likeCompetition for resources like

food, space, or matesfood, space, or mates

Other dangers likeOther dangers like

predation, disease, or parasitismpredation, disease, or parasitism

There is a constant There is a constant struggle for survival. struggle for survival.

Examples are:Examples are: Natural disasters like Natural disasters like droughts, fires, floods, etc.droughts, fires, floods, etc.

Competition for resources likeCompetition for resources like

food, space, or matesfood, space, or mates

Other dangers likeOther dangers like

predation, disease, or parasitismpredation, disease, or parasitism

2. The environment presents challenges to 2. The environment presents challenges to survival.survival.

2. The environment presents challenges to 2. The environment presents challenges to survival.survival.

Example:Example:green beetles green beetles tend to get eaten tend to get eaten by birds and by birds and survive to survive to reproduce less reproduce less often than brown often than brown beetles do.beetles do.

http://evolution.berkeley.edu/evolibrary/WHY would green beetles get

eaten more often than brown beetles?

3.3. Individuals that are fit* to their Individuals that are fit* to their environment leave more offspring than environment leave more offspring than those who aren’t. those who aren’t.

3.3. Individuals that are fit* to their Individuals that are fit* to their environment leave more offspring than environment leave more offspring than those who aren’t. those who aren’t.

Example:Example:The surviving brown beetles have brown The surviving brown beetles have brown baby beetles because this trait has a baby beetles because this trait has a genetic basis.genetic basis.

http://evolution.berkeley.edu/evolibrary/

*Fit or fitness – does not mean “buff” beetles; more fit means they are better adapted or more likely to survive; they’re a good “fit” for their environment…

4.4. Therefore, characteristics of fit individuals Therefore, characteristics of fit individuals increase in a population over time. increase in a population over time.

Conversely, over time, genes for less favored Conversely, over time, genes for less favored characteristics will become less common, characteristics will become less common, but not eliminated (because they’re but not eliminated (because they’re preserved in the heterozygotes)preserved in the heterozygotes)

4.4. Therefore, characteristics of fit individuals Therefore, characteristics of fit individuals increase in a population over time. increase in a population over time.

Conversely, over time, genes for less favored Conversely, over time, genes for less favored characteristics will become less common, characteristics will become less common, but not eliminated (because they’re but not eliminated (because they’re preserved in the heterozygotes)preserved in the heterozygotes)

Example:Example:The more advantageous trait, brown coloration, The more advantageous trait, brown coloration, allows the beetle to have more offspring and allows the beetle to have more offspring and becomes more common in the population. If this becomes more common in the population. If this process continues, eventually almost all process continues, eventually almost all individuals in the population will be brown.individuals in the population will be brown.(What would happen if a parasite prefers brown (What would happen if a parasite prefers brown beetles, or if the environment was covered in beetles, or if the environment was covered in green leaves?)green leaves?)http://evolution.berkeley.edu/evolibrary/

Therefore Darwin’s contributions:Provided evidence that species evolve:

In 1859, he proposed the theory of natural selection to explain evolution (survival of the fittest)

- Over time, change within a population leads to the replacement of old species by new species as traits that are not selected for become less common.

- Some evidence from fossils supports the theory that species on Earth have evolved from ancestral forms that are extinct. (species that have disappeared permanently.)

Evolution Part 2:Evolution Part 2:Speciation and Hardy-WeinbergSpeciation and Hardy-Weinberg

What is a species?What is a species?

A species is one or more populations of A species is one or more populations of individuals that can individuals that can interbreedinterbreed, producing , producing fertilefertile offspring. offspring.

SpeciationSpeciation is the process by which new is the process by which new species are formed over time.species are formed over time.

Or, why are these two owls different species,

but these dogs aren’t?

How does speciation occur?How does speciation occur?Let’s begin with a simple example -- Let’s begin with a simple example -- geographic geographic

isolationisolation..

This is when populations of individuals are This is when populations of individuals are geographically separated and prevented from geographically separated and prevented from matingmating with one another. with one another.

This can be due to the formation This can be due to the formation of new mountains, canyons, rivers, or other of new mountains, canyons, rivers, or other landforms, for example.landforms, for example.

How does speciation occur?How does speciation occur?Over time, natural selection, acting on random mutations in Over time, natural selection, acting on random mutations in

the population, makes the DNA so different that the the population, makes the DNA so different that the populations are no longer able to populations are no longer able to reproducereproduce with each other with each other

Their chromosomes may not Their chromosomes may not even match up.even match up.

Once there is no gene flow between Once there is no gene flow between

the populations, mutations start to accumulate the populations, mutations start to accumulate differently in each population and the differently in each population and the populations diverge into different species. populations diverge into different species. This is called macroevolution – change on a This is called macroevolution – change on a grand scale including extinction and grand scale including extinction and speciation. speciation.

Physical incompatibilityFor obvious reasons, crickets can’t mate with giraffes, for example. They just don’t have a common enough ancestor.

Different mating schedules or locationsFor example, certain flowers and insects may prefer to mate at different times of day, may bloom at different times of the year, or may prefer different mating locations. So even if they are not geographically separated, they still won’t mate with someone with a different schedule.

BehaviorAnimals, especially, are picky. Some have elaborate mating rituals or specific traits they look for in a mate. For example, in some spiders and mantises, if the rituals aren’t pleasing to the female, she will eat the male.

Sometimes population ranges of different Sometimes population ranges of different species overlap, but they still won’t species overlap, but they still won’t interbreed. Here are some reasons why:interbreed. Here are some reasons why:

Natural selection acts on Natural selection acts on individualsindividuals; ; Evolution (the change) is measured in Evolution (the change) is measured in populationspopulations. . Microevolution is defined as the change in allele Microevolution is defined as the change in allele

frequencies* in a population over generations.frequencies* in a population over generations.

*Frequency – how often something occurs expressed as a decimal; for example, if something occurs 50 out of 100 times, it has a frequency of 0.5

Hardy-WeinbergHardy-Weinberg

In 1908, 2 scientists independently came up with In 1908, 2 scientists independently came up with a mathematical way to measure if a population a mathematical way to measure if a population is evolving by measuring changes in allele is evolving by measuring changes in allele frequencies.frequencies.

The equation assumes the following conditions:

1.Very large population

2.No migration

3.No net mutations

4.Random mating

5.No natural selection

(if the above are occurring the population is most likely NOT going to evolve)

What causes genetic change in a population?What causes genetic change in a population?

Those conditions are never fully met. Therefore, the 4 main factors that cause change of allele frequencies in a population are:

•Natural selection

•Genetic drift

•Gene flow

•Mutation

Of these, only natural selection adapts a population to its environment, and we’ve already talked about it. The other three may be good or bad for a population or it may be neither good nor bad for it.

Genetic DriftGenetic DriftGenetic drift is Genetic drift is change in allele frequency due to change in allele frequency due to

sampling error (chance) sampling error (chance) This factor is more pronounced when the population is smaller than when the population is bigger.

Two examples:Bottleneck effect – occurs when a population is drastically reduced in size due to a natural disaster such as hurricane or disease, and many alleles are lost completely while others are over or under represented from what they were in the large population; ex) cheetahs; population is at risk due to a lack of genetic variabilityFounder effect – occurs when a few individuals from a large population found (start) a new, isolated population ; ex) insects blown from the mainland to an island; humans moving from one continent to another and marrying within their own isolated community, such as the Amish in the U.S.

Gene flowGene flowAnother word for gene flow is Another word for gene flow is migrationmigration. Gene flow is . Gene flow is

when the allele frequency of a population is altered by when the allele frequency of a population is altered by individuals moving into (or out of) a populationindividuals moving into (or out of) a population..

MutationMutation

As we have studied in past units, As we have studied in past units, a mutation is a change a mutation is a change in your DNAin your DNA. This is the other factor that can change . This is the other factor that can change allele frequencies. A flower population with only blue allele frequencies. A flower population with only blue alleles can sometimes produce a red flower due to alleles can sometimes produce a red flower due to mutation. That changes the allele frequency. mutation. That changes the allele frequency.

In general, only things you were born with can be inherited. Things that change your appearance but are not genetic, such as tattoos or ear gauges, cannot be inherited. Even most mutations in your DNA cannot be inherited by your offspring.

Think about why.

What’s the big exception?

Evolution Part 3: Evidence of Evolution

Scientific Evidence of Evolution includes:1. Fossil Record

2. Biogeography

3. Homologies

Fossil RecordIn order for fossils to form: Calcium must be replaced

by harder minerals Burial must occur by

sedimentation Sediment includes

particles in swamps, mud, ocean floors, tar pits, etc.

Fossils are how we know that extinct animals used to live here on Earth.

Equus, the modern horse, evolved from the dog-sized Hyracotherium. Notice it evolved from a four-toed front foot to the one-toed front foot of the modern horse.

Gradualism says that this happened gradually over millions of years. The evolution of the horse is an example of gradualism.

Punctuated Equilibrium says that these species existed in long periods of stasis interrupted by relatively brief periods of genetic instability that produced changes. This overall change still happened over millions of years.

Evidence for both theories is observed in the fossil record.

. BiogeographyIs the study of the geographic distribution of species and fossils. It is used to test predictions about the nature, age, and location of certain fossils.

What first suggested evolution to Darwin.Species tend to be more closely related to other species from the same area than to other species with the same way of life but living in different areas. Explains/reflects both homology and analogy

. HomologiesCharacteristics that are shared by related species because they have been inherited in some way from a common ancestor.

There are 3 main categories of homologies:

Anatomical

(as opposed to analogies; vestigial structures)

Biochemical

Developmental

. Anatomical HomologiesHomologous structures have the same underlying structure, but may have evolved different functions.

For example, the bones on the front fins of a whale are homologous to the bones in a human arm and both are homologous to the bones in a chimpanzee arm.

Anatomical HomologiesAnatomical Homologies

Divergent Evolution:Divergent Evolution: formation of new formation of new species from an existing species species from an existing species adapting to new environments.adapting to new environments.

- Homologies are evident- Homologies are evident

Divergent evolution Divergent evolution exampleexample

All canines have long legs, walk on their toes, have All canines have long legs, walk on their toes, have bushy tails, non-retractable claws, and a dew claw on bushy tails, non-retractable claws, and a dew claw on the front feet. These and other shared characteristics the front feet. These and other shared characteristics are due to the fact that they all come from a common are due to the fact that they all come from a common ancestor. Different populations ancestor. Different populations divergeddiverged at different at different points and created all these species. Sometimes points and created all these species. Sometimes called called adaptive radiationadaptive radiation. Often occurs when niches . Often occurs when niches become available due to a catastrophic event that become available due to a catastrophic event that has led to the extinction of other animals.has led to the extinction of other animals.

Anatomical Analogies

Often result from convergent evolution; organisms evolve similar features independently, often because they live in similar habitats. These similarities are NOT due to having a common ancestor. Sometimes called parallel evolution.

ANALOGOUS STRUCTURES are similar in function but not in origin or structure

Spines/thorns serve a similar function…what?

Left: American cactus (spines are modified leaves)Right: African euphorb (thorns are modified branches/stems)Therefore, different structure and origin

Anatomical AnalogiesAnatomical AnalogiesConvergent Evolution:Convergent Evolution: process by which process by which unrelated species become similar as unrelated species become similar as they adapt to similar environments.they adapt to similar environments.

Convergent evolution Convergent evolution exampleexample

Sharks, dolphins, tuna, penguins have streamlined Sharks, dolphins, tuna, penguins have streamlined bodies, and fins. These similarities are NOT bodies, and fins. These similarities are NOT because they have a common ancestor. Sharks because they have a common ancestor. Sharks are cartilaginous fish, dolphins are mammals, tuna are cartilaginous fish, dolphins are mammals, tuna are bony fish, and penguins are birds. They share are bony fish, and penguins are birds. They share similarities because they both adapted to the similarities because they both adapted to the same marine environment and predatory lifestyle.same marine environment and predatory lifestyle.

Vestigial StructuresVestigial structures are structures that no longer serve a useful purpose and/or are much less important than they used to be.Examples include: whale pelvis, claws on a boa’s belly

tailbone pinky toes appendix

human canines wisdom teeth goose bumps

muscles to move human ears & make hair stand on end

Biochemical Homologiescomparing genes to show relationships.

Idea is that closely related organisms have more similar genes / proteins than distantly related organisms.

For example, fish, chimpanzees, and humans all have hemoglobin. You would expect the human hemoglobin to be more similar to the chimpanzee hemoglobin than to the fish hemoglobin since the chimp and the human are more closely related.

Developmental HomologiesEmbryology is the study of organisms in

their earliest stage of development.Traces similarities in development.For example, all chordate embryos have

pharyngeal gill slits and post-anal tails. That’s part of the definition of being a chordate.