Evolution!

Subtopics are highlighted, terms are bolded, and definitions are underlined :)

History of Evolutionary Thought:

What is Evolution?

Evolution is a process that results in heritable changes in a population spread over generations.

Here's some more vocab...

Adaptation - an inherited characteristic that improves an organism's ability to survive and reproduce in a particular environment

Fitness - the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

Natural Selection - main mechanism of evolutionary change, ex. peppered moths

This is a process by which individuals with inherited characteristics that are well suited to the environment leave more offspring than do other individuals. 

Who is Charles Darwin?

Charles Darwin (1809 - 1882) was a British naturalist who introduced the concept of natural selection which is the main mechanism for how evolution occurs. 

Darwin's Concept of Natural Selection:

1. There are variations within every population.

2. Organisms compete for limited resources.

3. Organisms produce more offspring than can survive due to there being limited resources leads to competition.

4. The organisms with the favorable characteristics or adaptations for that environment survive better and reproduce more often, thus transmitting those favorable traits to the next generation.

Adaptive Radiation - a rapid evolutionary event in which one ancestral species evolves into an array of different species due to them adapting to different environments

This typically occurs after a mass extinction or when a species inhabits a new habitat such as. an island, ex. The Galapagos Finches 

Common Ancestry:

Evidence to Determine Evolutionary Relationships:

1. Fossil Record

2. Anatomical Evidence

3. Embryological Evidence

4. Molecular Evidence

Fossil Record:

The totality of fossilized artifacts and their placement within the Earth's rock strata provides information about the history of life on Earth. For example what the organisms look like, where and when they lived, and how they evolved.

Layers of sedimentary rock contain fossils. The new layers cover the older ones, creating a record over time. Fossils within layers show that a succession of organisms has populated Earth over a long period of time.

Radiometric dating - a procedure that determines the age of rocks and fossils based upon the half-life of radioactive isotopes.

There are two types of radiometric dating...

Carbon 14 dating can only age fossils less than 50,000 years old.

Potassium-Argon dating can date fossils from 100,000 years old up to 4.3 billion years old. It can only be used to date igneous rock layers.

Anatomical Evidence:

Homologous structures have a similar structure, similar embryological development, may have different functions, but the evidence proves that the trait evolved from a shared common ancestor, and branched off from a common 4 limbed ancestor.

Divergent Evolution - the process by which two or more related but reproductively isolated populations become more dissimilar

This can lead to the formation of new species.

Analogous structures have similar functions, similar external forms, but different internal structures and development, different origin, the trait is not found in a common ancestor of those organisms, the trait developed independently in each lineage after the last shared common ancestor, and evolves from convergent evolution.

Convergent Evolution - the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments

Embryological Evidence:

Similar embryological development in closely related species. All vertebrate embryos have similar structures at different stages of development, ex. gill pouch in fish, frog, snake, birds, human, etc.

Molecular Evidence:

Molecular evidence is comparing DNA and protein sequences. It's the most accurate evidence.

Closely related species have sequences that are more similar than distantly related species.

Phylogeny:

What is a phylogenetic tree?

A phylogenetic tree is a branching pattern that shows the evolutionary relationships of organisms. 

You can use the four evidences to prove a phylogenetic tree.

Nodes - common ancestors (where the lines meet)

Clade - each evolutionary branch

Every clade consists of an ancestral species and all of its descendants. Technically the entire tree is a clade.

Cladistics - a way in which biologists determine the sequence of branching in a phylogenetic tree

All of the organisms of a particular clade must share a homologous structure that does not occur outside of the clade. 

These unique homologous features that unite the group of organisms are called derived characters.

What are two derived characters that unite mammals together?

 Hair/common ancestors with hair, and memory glands that produce milk.

Cladogram - a phylogenetic diagram that specifies the derived characters of clades

Mechanisms of Evolutionary Change:

Gene - DNA instructions for building proteins

Allele - variations of a specific gene, ex. yellow and green peas

Mutation - a change in the DNA instructions of a particular gene

Gene Pool - consists of all the alleles of genes found in all the individuals that make up a population

Allele Frequency - the percent of the population that contains a specific allele of a gene

Variation is the raw material for natural selection, meaning you need variation in order for natural selection to occur.

All traits vary within a population. Some individuals have traits that are better suited to the environment than others.

Why do traits vary?

1. Mutation

Random changes to DNA. They occur due to errors during DNA replication or environmental damage. They lead to new versions of an allele or new genes altogether.

2. Genetic Recombination

It leads to new arrangements of alleles in every gamete, thus every gamete from the same individual is genetically different.

This is due to meiosis, specifically crossing over and independent assortment.

3. Random fertilization of a sperm or egg between partners

This is the mixing of alleles between two individuals. It forms unique combinations in the offspring.

Going back to natural selection...

Natural selection acts on individuals.  It's basically survival of the fittest.

Natural selection also causes populations to evolve because the individuals who are fitted to survive are able to produce more offspring. As populations evolve, favorable traits become more common.

Natural selection can only act on traits that contain....

1. Heritability

Genetic/can be passed on

2. Variability

More than one allele

3. Reproductive Advantage

One allele has to have a more reproductive advantage than the other

Artificial Selection - selective breeding of domesticated plants and animals to produce offspring with desired genetic traits

Sexual Selection - non-random mating

Individuals with certain characteristics are more likely than other individuals to obtain mates.

Coevolution - two or more species having a close ecological relationship evolve together such that one species adapt to the changes of the other thereby affecting each other's evolution, ex. predator-prey, disease and host, competitive species, mutualism, pollinators, and flowers.

Specialization:

Microevolution - refers to allele frequency changes within a population

Macroevolution - evolutionary change at the species level 

What is a species?

A species is a population whose members can interbreed and produce viable fertile offspring.

What is speciation?

Speciation is the formation of a new species. In order for speciation to occur there needs to be reproductive isolation.

Fertilization - the union of a sperm and an egg cell forming a zygote

Zygote - the first cell of an offspring formed from the union of a sperm and egg cell

There are different types of reproductive isolation...

Geographic Isolation - a physical barrier separates a population and they eventually evolve differently ex. Harris's antelope squirrel inhabits the canyon's south rim. Just a few miles away on the north rim lives the closely related white-tailed antelope squirrel. Because they are separated by a physical barrier, the canyon, they cannot mate and are considers different species.

In the future, a reproductive barrier may develop that prevents mating even if they come back in contact with each other making them separate species.

Ecological Isolation - species occur in the same area by occupying different habitats so they rarely encounter each other, ex. two species of garter snakes live in the same area but one life in water and the other is terrestrial. Because they live in different habitats, they cannot mate are considered different species.

Temporal Isolation - species that breed during different times of day, different seasons, or different years cannot mix gametes, ex. eastern spotted skunk and a western spotted skunk overlap in range but the eastern mates in late winter and the western mates in the late summer. Because the skunks mate at different times, they cannot mate and are considered different species.

Behavioral Isolation - unique behavioral patterns and rituals isolate species, ex. blue-footed boobies mate only after a courtship display unique to their species. Because blue-footed boobies have a specific mating ritual, other boobies won't be able to mate with them, making them different species.

Mechanical Isolation - morphologic differences can prevent successful mating, ex. even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. Two species of monkeyflowers differ in shape and color, so therefore pollination does not happen. Because the two flowers look different (have a different form or shape) they cannot mate, and therefore are considered different species.

Gametic Isolation - sperm of one species may not be able to fertilize the eggs of another species, ex. sea urchins release sperm and eggs into surrounding waters where they fuse and form zygotes. Gametes of different species are unable to fuse. Because the two species aren't able to mate, they are considered different species.

Prezygotic Barriers - an obstacle to mating or to fertilization if mating occurs

The isolations we just learned are all prezygotic barriers.

Postzygotic Barrier - prevents hybrid offspring from developing into a viable, fertile adult, ex. reduced hybrid fertility.

Reduced Hybrid Fertility - chromosomes of parents may differ in number or structure and meiosis in hybrids may fail to produce normal gametes, ex. mule. A donkey has 32 pairs of chromosomes and a horse has 31 pairs. If they mate, they produce a mule, which has 63 chromosomes, making it vigorous but sterile.