Unit 11 - EvolutionPart 1: Principles of Evolution –Evolution by Natural Selection

(Ch. 10 Sec. 1-5, Ch. 12 Sec. 1 & 2)

Evolution Part 1Principles of Evolution—Evolution by Natural Selection

(Ch. 10 Sec. 1-5, Ch. 12 Sec. 1 & 2)

• Look at the star-nosed mole. (p. 285)

1. What sorts of modifications are obvious?

2. How might these traits arise in the first place?

– These will then be passed on to future generations.

– Ray-like feelers extending from snout, poor eyesight, and prominent claws

mutations

--Mutations in DNA

What is Evolution? (Ch. 10.1-10.2)

Evolution• Evolution is change in species over time• Process of biological change by which

descendants come to differ from their ancestors (p. 286)

• Change happens in characteristics of a population from one generation to the next

• Populations evolve, individuals do not!

Name things that have changed over time

Example: Radios

Vocabulary• Population – all of the

individuals of a species that live in an area (p. 294)

• Variations – differencesin the physical traits of an individual from those traits of individuals in the population

Vocabulary• Species – group of organisms are

that are closely related and can mate to produce fertile offspring– Dogs (Canis familiaris) are all the same

species; just like all modern humans are all Homo sapiens.

– We have different dog breeds based on their genetic variations but they are all the SAME species. No two people look exactly alike due to genetic variation within the human population

• Speciation – process in which new species are formed over time

• Adaptation – a feature that allows an organisms to better survive and reproduce in its environment; this can lead to genetic change in a population over time.

Vocabulary

Charles Darwin – the father of evolution(p. 290-291)

• born in 1809, in England• was asked to sail on the

H.M.S. Beagle to chart stretches of the South American coast

This voyage lasted from 1831 to 1836.

Charles Darwin – the father of evolution(p. 290-291)

Charles Darwin – the father of evolution

(p. 290-291)

• Voyage of H.M.S. Beagle– 5 year unpaid voyage– Darwin studied plants, animals, collected fossils– found fossils of extinct animals that were similar

to modern species. – during his voyage, he made observations that led

him to his theory of evolution.

Charles Darwin – the father of evolution

(p. 290-291)

On the Galapagos Islands in the Pacific Ocean he noticed many variations among plants and animals of the same general type as those in South America.

Darwin noticed there were several types of finches on these islands, and that they all looked like a bird he had seen on the South American continent.

Charles Darwin – the father of evolution(p. 290-291)

• The most distinct difference among finch species is their beaks

• Why would beaks be different in different locations on an island?– they are adapted for the

specific diets available on the islands.

Charles Darwin – the father of evolution(p. 290-291)

• Darwin hypothesized that some of the birds from South America migrated to the Galapagos

• once on the islands, the birds must have changed over the years, explaining the numerous species of birds present

Charles Darwin – the father of evolution(p. 290-291)

• After returning from the Galapagos and studying all the different types of plants & animals he collected during the voyage, Darwin concluded that organisms change over time.– Darwin called this evolution, which means change in

species over time. – Darwin called the mechanism for evolution natural

selection (a.k.a. survival of the fittest).

How does Evolution Happen?

• Natural Selection• Mutations• Artificial Selection• Geographic Separation/Isolation• Genetic Drift• Gene Flow (migration)

Natural Selection – the main mechanism of evolution (Ch 10.3 &

11.2)• Natural selection explains how evolution can

occur.• natural selection – a mechanism by which

individuals that are better fit for their environment have a greater chance to survive and mate/reproduce (p. 293)– aka- Survival of the fittest– What does it mean to be “fit”?

• fit means they have inherited beneficial adaptations which allow them to be more likely to survive and reproduce more offspring.

– the genetic traits of “fit” individuals become more common or frequent over time.

– The genetic traits of less fit individuals become less common or frequent over time.

There are four main principles to the theory of natural selection

1. Variation – heritable differences that exist in populations

2. Overproduction – not all offspring will survive due to competition

3. Adaptation – certain variations can allow an individual to survive better than others (the environment can present challenges for survival)

4. Descent with Modification – the number of individuals with the advantageous adaptations will increase over each generation

• A well-studied example of natural selection in jaguars is shown in Figure 3.2 p. 295

• View animated biology – 10.3 Principles of Natural Selection (Jaguar)

Example: Natural Selection and beetles

– beetles have genetic variation✓Some are brown, others green

What would happen if the environment changed from brown stones to green grass?

– there is a struggle for survival✓Predation

– more fit individuals leave more offspring

--characteristics of fit individuals increase in a population over time

Natural Selection acts on existing variation

• Natural selection can only act on traits that already exist.

• Natural selection acts on phenotypes; new alleles occur by genetic mutations.– Read p. 296-297 about the 2 examples supporting this

concept.– View Animated Biology 10.3 Natural Selection(fish) (may

not work in Chrome; works best in Safari)

Artificial Selection (p. 292)

• Artificial Selection – the process by which humans change a species by breeding it for certain traits– Humans determine which traits are favorable and

breed individuals that show those traits.– Ex. race horses, show dogs

Unit 11Part 2: Evidence to Support Evolution

(Ch. 10.4-10.5, Ch. 12.1)

Evidence to Support Evolution (Ch 10.4-10.5, Ch. 12.1)

• Evidence to Support Evolution:– fossil record (p. 298, 306, 348)– Biogeography– Homologies : anatomy, development & molecular

(p. 299-304)

Fossil Record (Ch 10.4 & 12.1)• What is a fossil?

– Fossil – trace of a dead organism

– Scientists consider three things about fossils: age, location and what the environment was when that organism was alive.

– Fossils are dated through radiometric dating and relative dating.

Fossil Record

• Radiometric dating usesthe known time of natural decay of unstable isotopes to calculate the age of the material.

• Relative dating estimates the age of fossils by comparing the fossils found in certain rock layers to those in other layers. The oldest fossils are found on the bottom, further from the surface. The youngest fossils are closest to the surface.

Fossil Record• Fossils can form in several ways (p. 298, 306, &

348). The most common fossils result from permineralization.

Fossil Record• What may happen if the organism doesn’t die

in sediment?– Fossil doesn’t form; decomposition takes place

• Why is the fossil record not complete?– Most living things do not form into fossils when

they die since the conditions are not conducive to fossil formation

– Many fossils may not have been discovered yet

Biogeography (p. 299)• biogeography - Is the study

of the geographic distribution of plants, animals and fossils. – it is used to test predictions

about the nature, age, and location of certain fossils.

– 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.

Anatomy and Development (p. 299-304)

homologous structures (p. 302)• homologous structures:

- common ancestor- Similar structure- Different function

• Example: the long bones of a cat, human, whale and bat are similar in structure (made of bones) but have different functions.

Homologous Structures

– Similar Structure– Different Function– Common Ancestor

Forelimbs of Vertebrates

Anatomy and Development (p. 299-304)

• analogous structures p. 303– not related– different structures– same function

• examples:– bird wing and

insect wing

Analogous Structures - Quills

Hedgehog (mammal)

Sea urchin(invertebrate)

Cactus (plant)

• not related• different structures• same function

Anatomy and Development(p. 299-304)

• vestigial structures p. 304• vestigial structures- serve

no useful purpose.

• examples:– pelvic bone in a whale– human appendix– pelvic bone & hind limb bones

in some snakes- human canine teeth & wisdom

teeth

Vestigial Structures

cont’d

Examples of Vestigial Structures• Extra pad and nail on dog & wolf paws

Vestigial Structures (cont’d)Eyespot on a cave salamander. This little guy NEVER sees light.

Embryology(p. 299-39)

• Embryology - Similarities in embryological development among organisms is further evidence of shared common ancestry

• Ex. Crab and barnacle – adults look very different but the larva can look very similar (Fig 4.4)

• Ex. Embryos of vertebrates

Molecular Evidence (p. 307)– Very different species have similar molecular

and genetic mechanisms. Because all living things have DNA (bacteria, plants, animals, etc.), they share the same genetic code and make most of the same proteins from the same 20 amino acids.

– More similarities in DNA (which translates into proteins) between two organisms, the more closely related they are, the more differences; the more distantly related.

Molecular Evidence (p. 307)• Comparing Amino Acids

1. Which organism is most closely related to the human? Why?

2. Which organism is least closely related to the human? Why?

Chimpanzee; greatest number of similarities with human

Kangaroo; greatest number of differences when compared too human

Number of amino acids that differ from a human

Molecular Evidence (p. 307)

• Remember, the DNA sequence dictates the amino acid sequence through the processes of transcription and translation, therefore, ALL 4 levels (DNA, RNA, amino acids, and proteins) can show evidence of evolution

Molecular Evidence (p. 307)

• Watch Hox genes video clip (2:44) Section 10.5 “Evolutionary Biology 1” in your online textbook

– Sign in to Google or gmail; then go to the online textbook

– Select Chapter 10 in dropdown box and click “GO”– Click on Student Resources– Click on Videos– Click on Biology Video Clips– Click on Section 10.5 “Evolutionary Biology 1”

Unit 11Part 3: The Evolution of Populations

(Chapter 11)

Vocabulary• gene pool – combined

alleles of all the individuals in a population

Genetic Variation Within Populations (p. 316-321)

Vocabulary

• alleles – different forms of a gene– flower color gene may be

“P” (purple) or “p” (white)

• frequency – how often something occurs over time– Ex. If 25 rabbits are white, out of a population of 100

rabbits, the frequency of white rabbits is 0.25

Genetic Variation Within Populations (p. 316-321)

• Genetic variation in a population increases the chance that some individuals will survive.

• Genetic variation comes from two main sources.– Mutation - random change in the DNA of a gene; if

the change occurs in the DNA of a reproductive cell (gamete=egg or sperm), then the mutation will be passed on to offspring.

– Recombination – new allele combinations in an offspring that occurred during meiosis through crossing over and independent assortment.

Other Mechanisms of Evolution(p. 323-327)

• Natural selection isn’t the only mechanism through which populations evolve. Other mechanisms include: genetic drift, gene flow, mutation and sexual selection.

gene flow – movement of alleles from one population to another

Individuals in Population 1 migrate to Population 2 and change the frequency of green beetles found there

Population 1 Population 2 Population 2 over time

Other Mechanisms of Evolution (p. 323-327)

• another word for gene flow is migration (immigration & emigration)

• gene flow increases the genetic variation of the receiving population

• lack of gene flow between two populations may lead to the formation of different species

Other Mechanisms of Evolution (p. 323-327)

Genetic Drift

• genetic drift - change in allele (gene) frequency due to chance; results in loss of diversity

• Two types of genetic drift1. Bottleneck effect

2. Founder effect

Other Mechanisms of Evolution (p. 323-327)

Genetic Drifto Bottleneck effect -

when a population is drastically decreased due to a natural disaster (hurricane, disease)

• some genes are completely lost; others are over-represented

• some genes are reduced so much they can’t “make a come back” in their new population

Other Mechanisms of Evolution (p. 323-327)

Other Mechanisms of Evolution (p. 323-327)

Genetic Drifto founder effect – when a small group splits off

from a larger population and starts their own population isolated from the original population

• Amish in America – original population was 14 individuals that immigrated from Europe

Other Mechanisms of Evolution (p. 323-327)

Mutations• a random mutation can happen to one individual

in a population, and can ge beneficial, harmful, or neutral

• random mutations can increase chances of survival and reproduction

• random mutations can decrease chances of survival – if an individual

dies before it can reproduce, that mutation is not passed down to another generation

Other Mechanisms of Evolution (p. 323-327)

• random mutations might not affect an individuals ability to survive and reproduce and will become a natural variation instead of a mutation

• Ex. dark spots on pigs

Other Mechanisms of Evolution (p. 323-327)

Sexual Selection (p. 326)

• Sexual selection occurs when certain traits increase mating success.

• Ex. Males compete for females such as the head-butting of bighorn sheep; Male peacocks fan out their tails to attract the female.

Hardy-Weinberg (p. 328)• 1908 - two scientists created an equation to test these ideas of

probability and chance• Hardy-Weinberg principal - the frequency of alleles in a population

does not change unless evolutionary forces act on the population

• Characteristics of a Hardy-Weinberg (non-evolving) population:- very large population

- no migration (no immigration or emigration)

- no mutations

- random mating (no individual are “more fit”, they all seem to the same)

- no natural selection

● A population with all of these criteria is not evolving. This doesn’t happen in nature; therefore all populations in nature are evolving.

• Reproductive isolation –when members of different populations of the same species can no longer mate successfully.

• Reproductive isolation can lead to speciation.• Three barriers that can cause reproductive isolation to

occur:1. Behavioral barriers – courtship or mating behaviors are now

different in the population2. Geographical barriers – physical separation of the populations;

Ex. mountains, roads, rivers3. Temporal barriers – the two populations aren’t ready to mate at

the same time of day (ex. Flowers that bloom in morning vs. evening) or in the same season

Isolation of a population can lead to speciation(p. 332)

Patterns of Evolution (p. 335-341)

Convergent evolution (word part: co = together)

similarities not because they are related but because they need certain adaptations to survive in their environment; therefore, they have analogous structures

Patterns of Evolution (p. 335-341)

Convergent evolution• Example:• Sharks, dolphins, tuna, penguins have

streamlined bodies, and fins. • HOWEVER Sharks are cartilaginous fish,

dolphins are mammals, tuna are bony fish, and penguins are birds.

• they share similarities because they all adapted to the same marine environment and predatory lifestyle.

Convergent evolution is sometimes called parallel evolution

Patterns of Evolution (p. 335-341)

• Divergent evolution (word part: di = two); the process by which one species begins to split into two distict groups with different traits; therefore, they have homologous structures

Patterns of Evolution (p. 335-341)Divergent evolution Example:

• All canines have long legs, walk on their toes, non-retractable claws, and dew claws because they all come from a common ancestor.

• Different populations diverged at different points an created all these species (domestic dogs, wolves, coyotes, foxes, etc.)

Divergent evolution is sometimes called adaptive radiation and may lead to speciation.

Phylogenic (or Phylogenetic) Tree• a diagram

showing the evolutionary history of a species of an animal.

• Is this convergent or divergent evolution?

Divergent

Patterns of Evolution (p. 335-341)

Coevolution – process in which two or more species evolve in response to changes in each other.Ex. ant and acacia tree, crabs & snails, flower structure & bird beak shape (p. 337)

Patterns of Evolution (p. 335-341)

Extinction – elimination of a species, usually as a result of its inability to adapt to a change in the environment; Ex. dinosaurs (p. 338)

Patterns of Speciation

(p. 339)

• gradualism- slow changes happen continuously over a long period of time– Ex. Evolution of the

horse (p. 339)

Patterns of Speciation (p. 339)

• punctuated equilibrium- bursts of rapid change in species are separated by periods of little to no change– “spurts in evolution”– traits “appear suddenly” in the fossil record

usually due to climate changes or catastrophic events

Gradualism vs. Punctuated Equilibrium

• Life forms reproduce and therefore have a tendency to become more numerous.

• The offspring differs from the parent in minor random ways.

• If the differences are helpful, the offspring is more likely to survive and reproduce.

• This means that more offspring in the next generation will have the helpful difference.

• These differences accumulate resulting in changes within the population.

• Over time, populations branch off to become new species as they become separated.

• This process is responsible for the many diverse life forms in the world.

• Haeckel's Paleontological Tree of Vertebrates (c. 1879).

In Summary…