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Evolution NotesKEY

Part 1: Principles 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?

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

2. How might these traits arise in the first place?Mutations in DNAThese mutations will then be passed on to future generations.

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!

Vocabulary • population —all of the individuals of a species that live in an area (p. 294)• variations - the differences in the physical traits of an individual from those traits

of other individuals in the population • species – group of organisms 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 organism to better survive and reproduce in

its environment; this can lead to genetic change in a population over time

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Charles Darwin- the father of evolution p. 290-291• born in 1809, in England• was asked to sail on the HMS Beagle to chart stretches of the South American

coast• voyage of H.M.S. Beagle

– 5 year unpaid voyage– Darwin studied plants, animals, collected fossils (ship’s

naturalist)– 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– on the Galapagos Islands in the Pacific Ocean he noticed 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

the most distinct difference among finch species is their beaks Why would beaks be different in different locations on an island?

o they are adapted for the specific diets available on the islands Darwin hypothesized that some of the birds from South America

migrated to the Galapagos Islands once on the islands, the birds must have changed over the years,

explaining the numerous species of birds present• 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….– He 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

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– 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 selection1. Variation—heritable differences that exist in populations2. Overproduction—not all offspring will survive due to competition3. 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

o View animated biology—10.3 Principles of Natural Selection (jaguar)

Example: Natural Selection and beetles – beetles have genetic variation

• some are brown, others are green– 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.

o Read p. 296-297 about the 2 examples supporting this concept.o View Animated Biology 10.3 Natural Selection (fish)

Artificial Selection p. 292Artificial 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

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

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Part 2: Evidence of Evolution (Ch. 10.4-10.5, Ch. 12.1)Evidence to Support Evolution

fossil record p. 298, 306, 348 biogeography p. 298-9 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 like when that organism was alive.

Fossils are dated through radiometric dating and relative dating.

Radiometric dating uses the 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.

Fossils can form in several ways (p. 298, 306, & 348). The most common fossils result from permineralization.

What may happen if the organism doesn’t die in sediment? 4

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. 299-304homologous structures p. 302• homologous structures:

– common ancestor– similar structure– different function

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

analogous structures p. 303• analogous structures:

– not related– different structures– same function

• examples:– bird wing and insect wing– quills on a sea urchin, hedgehog and cactus

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

Embryology p. 299-301

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

• Ex. Embryos of vertebrates• Ex. Crab and barnacle—adults look very different but the larva can look very

similar Fig. 4.4

Molecular Evidence p. 307 Very different species

have similar molecular (DNA, genes, amino acids) 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.

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?

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

Watch Hox genes video clip (2:44)Section 10.5 “Evolutionary Biology 1”

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Part 3: The Evolution of Populations (Ch. 11)Genetic Variation Within Populations p. 316-321Vocabulary

gene pool - combined alleles of all the individuals in a population

alleles - different forms of a gene o flower color gene may be “P” (purple) or “p”

(white) frequency - how often something occurs over time

o Allele frequency- measure of how common a certain allele is in the population; decimal value similar to a percent. Ex. if 25 rabbits are white out of a population of 100 rabbits, the frequency of white rabbits is 0.25

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. 323-327Natural selection isn’t the only mechanism through which populations evolve. Other mechanisms include: genetic flow, genetic drift, mutation and sexual selection.

Gene Flow gene flow – movement of alleles from one population to another• 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

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

diversity• Two types of genetic drift

1. Bottleneck Effect2. Founder Effect

o 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 comeback” in their new population

o 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

Mutations • a random mutation can happen to one individual in a population and can be

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 the another generation

• random mutations might not affect an individual’s ability to survive and reproduce and will become a natural variation instead of a mutation Ex. dark spots on pigs

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

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• Hardy-Weinberg principle - 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 individuals are “more fit”, they all seem 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.

Isolation of a population can lead to speciation p. 332

Reproductive Isolation 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 populations

2. Geographical barriers—physical separation of the populations; Ex. Mountains, roads, rivers

3. 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

Patterns of Evolution p. 335-341

Convergent evolution- (word part: co-together) individuals share similarities not because they are related but because they need certain adaptations to survive in their environment; therefore, they have analogous structures

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.

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

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 and created all these species (domestic dogs, wolves, coyotes, foxes, etc)

Divergent evolution is sometimes called adaptive radiation and may lead to speciation. Phylogenetic (or Phylogenic) Tree

• a diagram showing the evolutionary history of a species

• Is this convergent or divergent evolution? Divergent

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

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. of gradualism—evolution of the horse

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• 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

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