Evolution

Linnaeus: Taxonomy - Developed first taxonomic system  - naming and classifying the diverse forms of life “for the greater glory of God”: Hutton: Gradualism  - profound changes in the Earth’s features; cumulative, slow process Lamarck: Evolution Through Use & Disuse  - believed, incorrectly, that body parts could change due to use and disuse and  that these acquired characteristics could be inherited.Malthus: Populations  - human suffering was due to increasing populations

Cuvier: Paleontology  - Paleontologist that recognized that many extinctions occurred... he argued it  must have been due to catastrophism

Lyell: Uniformitarianism  - Geologist that argued geologic processes have not changed throughout Earth’s  historyDarwin: Evolution by Natural Selection - Published “The Origin of Species”  - Believed natural selection was the driving force for evolution. Mendell: laws of inheritance provided explanation for selection process

History of Thought

The Historical Context of Darwin’s Life and Ideas

Charles Darwin - Darwin originally studied medicine and theology  - Darwin was hired as Naturalist aboard the H.M.S. Beagle - Traveled 5 years around South America, Europe, Africa, and  Australia collecting fossils - Became famous for work with the Galapagos finches  - he believed that all the finches of these islands were  originally part of the same species (common ancestor) - Wrote "On the Origin of Species" (1858)

The Voyage of the HMS Beagle (1831 - 1836)

Darwin discovered that most of the animal species on the Galapagos lived nowhere else in the world, but they resembled species on the South American mainland

- Evolution- a change in the frequency of alleles (genes) in a  population over time

- There are two areas of evolutionary study:  1. Microevolution- how populations of organisms change from    generation to generation and how new species originate

 2. Macroevolution- patterns of change in groups of related  species over broad periods of geologic time.  - These patterns determine phylogeny (the evolutionary  relationships among species)

- Natural selection- differential survival and reproduction among  individuals in a population based on inheritable traits.  - The most well suited organisms survive and reproduce at a  greater rate,  thus eventually changing the allelic frequencies of  the population

Evolution by Natural Selection

- How it works:  1. Mutations, crossing over, etc... lead to genetic  variation 2. Genetic variation exists in all populations 3. Struggle for existence (survival) - populations will  always reproduce at a greater rate than the  environment can support, thus leading to competition 4. Some organisms possess variations that make them  better able to survive and reproduce than others.  Darwin would say these organisms are more fit.  (survival of the fittest).  5. Over time, these variations will continue to be passed  on and will eventually change the population

Evolution by Natural Selection

Example of Natural Selection: Insecticide Resistance in Insect Pops.

Example of Evolution:Drug Resistance in HIV

- 3TC interferes with   reverse transcriptase

- 3TC mimics cytosine and  when inserted it  terminates further   elongation

- HIV viruses that are   resistant to 3TC have  a different form of   reverse transcriptase,  it can recognize the   difference in   cytosines

Natural selection can impact a population in a variety of ways:

- Directional selection- favors traits at one extreme- Stabilizing selection- favors individuals with the middle phenotype- Diversifying selection- favors both extremes

Patterns of Selection

- In order for natural selection to operate, there  must be genetic variation among individuals in a  population. It comes from:

 - Mutations- change in DNA - Sexual reproduction-  - crossing over - independent assortment  - random joining of gametes from two individuals - Diploidy- allows one gene to be “hidden”

Evolution (change in allele frequencies) can be driven by:

 - Changes in the environment

 - Gene flow - alleles entering or leaving the population due to emigration or  immigration

 - Nonrandom mating - In-breeding - Breeding based on proximity - Sexual selection  - preferential mating with males or females with specific traits or  behaviors - Usually leads to male competition and female choice.  - Often leads to sexual dimorphism- differences in the  appearance of males and females - Ex: manes in lions, plumage in birds 

Influencers of Natural Selection

- Genetic drift- changes in the gene pool of a small population Three types:  1. Changes due to random chance 2. Founder effect- when a few individuals migrate and start their  own population, which doesn’t represent the genes in the  original population 3. Bottleneck effect- when a population undergoes a dramatic  decrease in size (due to natural disasters, for example) and  the individuals left don’t represent the original population

Influencers of Natural Selection

Natural selection should extinguish a population's variation by getting rid of the unfavorable phenotypes...so why doesn't variation disappear?

Techniques to Preserve or Restore Variation:1.) Diploidy – heterozygote condition hides the recessive form; prevents it  from being lost

2.) Balanced polymorphism – the frequencies of coexisting forms do not  change noticeably over many generations

 Causes of balanced polymorphism: 1.) Heterozygote advantage – better reproductive success than  homozygotes

 2.) Hybrid vigor – increased vitality of hybrid offspring

 ex. Sickle cell anemia - heterozygotes are resistant to malaria

 ex. Plant Crops - homozygotes are more sensitive to disease

The "Bad" Traits...Why Aren't They All Gone?

Gene Pool - all possible alleles of all members of a population

Hardy Weinberg Theorem: the frequencies of alleles in a population's gene pool will remain constant over generations as long as the following conditions are met:  - There can be no natural selection - Mutations cannot occur - The population must be isolated (no gene flow)  - The population must be large (no genetic drift)  - Mating must be random

- If any of those 5 things are violated- the populations allele frequencies will change- the population will evolve.

The Hardy Weinberg equation is used to evaluate whether or not the population is evolving. It is determined using the following values:

 - Allele frequencies for each allele - P= % of dominant gene - Q= % of recessive gene

 - Genotypic frequencies: - P2= % of homozygous dominant individuals - Q2= % of homozygous recessive individuals - 2PQ= % of heterozygous individuals

 - The equations:  - P + Q = 1 (all alleles add up to 100%)  - P2 + 2PQ + Q2= 1 (all individuals add up to 100%)

- Species- a group of individuals that can interbreed and  produce live, fertile offspring

- Speciation- the formation of a  new species that are   reproductively isolated

 - Anagenesis - one species  evolves into a new one

 - Cladogenesis - one species  diversifies and gives rise to  new species 

exampleDrosophila persimilis breeds in early morning, while closely related Drosophila pseudoobscura breeds in the afternoon

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Temporal Isolation

Mechanical IsolationexampleThe amazing partnership of the Bucket Orchid and Orchid Bee is so precise that if either one went extinct, the other would follow. No other orchid can possibly cross-pollinate the Bucket Orchid.

exampleThe Giant Red Urchin (Strongylocentrotus franciscanus and Purple Urchin (Strongylocentrotus purpuratus) cohabit the rocky intertidal along the western U.S., but they do not interbreed. Their gametes are genetically/chemically incompatible, maintaining species integrity.

Gametic Isolation

- The following are all reasons why two organisms may NOT be able to  reproduce and/or produce live, fertile offspring - They are therefore NOT part of the same species

- Some are pre-zygotic (before a zygote forms):  - Spatial isolation- species don’t encounter one another - Temporal isolation- when species mate or flower during different seasons  or different times of the day - Behavioral isolation- when a species doesn’t recognize another species as  a mating partner because it doesn’t perform proper courtship rituals  (songs, scents, etc.)  - Mechanical isolation- the male and female genitalia are structurally  incompatible - Gametic isolation- when male gametes are incapable of penetrating the  female gamete

- Some are post-zygotic (after a zygote forms): - Hybrid inviability- when the zygote fails to develop and dies before birth  - Hybrid sterility- when the hybrid is born but isn’t able to have it’s own  children - Hybrid breakdown- when the hybrids live for a generation, but aren’t well  suited to the environment and die out

Reproductive Isolation

- Can occur in several ways:  - Allopatric speciation-

 - Sympatric speciation-

 - Adaptive radiation-

- Allopatric Speciation- begins when a population is divided by a  geographic barrier (such as a mountain or river).  - The two populations now become different as each evolves to  the different environments.  - EX. Pupfish- lakes/rivers go through drying trend - EX: Grand Canyon Squirrels

 

- Sympatric Speciation- occurs without the presence of a geographic  barrier.  - EX: polyploidy in plants.

 

Autopolyploidy - more than 2 sets of   chromosomes - result of self-fertilization - can't interbreed with diploid  plants - may be able to self-fertilize

Allopolyploidy - more than 2 sets of   chromosomes - hybrid of 2 different species - very common - more vigorous than parents

Adaptive Radiation-  - when one species rapidly   evolves into many species.  - Happens when colonizing   a new, diverse geographic   area

- Divergent evolution- when two species that originate  from a common ancestor speciate.  - Example- African and Indian elephants  speciated

- Convergent evolution- when two unrelated species  share similar traits due to similar environmental  conditions (analogous traits) - Example- the torpedo body shape of penguins  and porpoise

- Parallel evolution- two related species that have  made similar evolutionary changes after diverging  from a common ancestor.  - Example- placental and marsupial mammals

- Coevolution- when two species evolve in response to  each other.  - Examples- predator/prey relationships or  relationships between plants and pollinators

Patterns of Evolution

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Macroevolution

Macroevolution

- There are two distinct theories used to interpret fossil evidence  for evolutionary history:  

 

Timing of Macroevolution

- Gradualism -argues that   evolution occurs by the   gradual accumulation of small  changes.

- Punctuated equilibrium-   - argues that evolutionary history  has long periods of stasis   (stability with little or no   evolution) followed by brief  periods of rapid evolution.

- Artificial Selection- selection carried out by humans for desirable  traits.  - Have led to various breeds of dogs.  - Brussel sprouts, broccoli, cabbage and cauliflower all   originated from a single wild plant.

Artificial Selection

- Paleontology- fossil evidence shows gradual changes  in species,  species that are now extinct, and  transitional fossils

 - Law of Superposition - allows for relative dating - deeper fossils are older

 - Transitional Fossils - fossils that show  intermediate forms 

   - Vestigial structures: historical remnants of  structures that had important functions  in ancestors - Have become smaller over time - Ex. snakes – pelvis, leg bones

Biogeography- geographic  distribution of species - species in different regions   of the world look alike,  especially when in   similar environments

Embryology- reveals similar stages in  development among species.  - EX: gill slits form in fish, chicken, pig  and human embryos

Molecular biology- closely related species share similar DNA and proteins.

Comparative Anatomy- looks at morphology (appearance inside and out):

 - Homologous structures- body parts that resemble one another in  different species because they have evolved from a common ancestor - Example of Descent with Modification

 - Analogous structures- body parts that resemble one another in different  species because they evolved independently as adaptations to similar  environments

A Cline

Cline: a graded change in some trait along a geographic axis