Biology Unit 5 – Evolution
Evolution according to Homer: http://www.youtube.com/watch?v=faRlFsYmkeY&feature=player_detailpage
How did Life Begin?
In this study of evolution, we must first consider theories of the beginning of the Earth and all life on it.
1.
Creationism
In this theory, the Earth and all living beings were created by one or more supernatural beings or gods. An example of this is the belief found in the Book of Genesis of the Bible that God created all over 7 Days and that humans were formed in his image. Within this specific theory there are three other theories including:
A.
Young Earth Creationism – Earth about 10,000 years old
B.
Omphalos Hypothesis – God created the Earth in its mature form
C.
Old Earth Creationism – broken into three parts, gap, day age and progressive creationism and accepts God as the physical creator of the universe and accepts scientific dating.
Please remember that all of these theories come out of the one belief in the Bible. We could research and learn so many more theories of Creationism, meaning that all was created by supernatural beings or Gods. For instance, in Hinduism it is believed that humans are part of the natural cycle of creation and destruction that began millions of years ago. It is also believed that humans have remained unchanged during that time.
2.
Intelligent Design
This is a relatively new theory that challenges Science to explain how all of this, the creation of the Earth and its beings, the universe, could happen at random. It believes that all things were done for a reason and that there is an intelligent explanation, reason, plan behind all that has happened and will continue to happen. In many ways it is very similar to Creationism, but does not label a specific creator (like God) within the theory.
3.
Big Bang Theory
This theory states that our Universe began about 13.7 billion years ago as a very small, dense pocket of gasses. As they met, they began a large reaction causing the small pocket to expand and become the universe that we have today. During the expansion, other particles met and reacted causing things like planets to form, atmospheres to develop and eventually life to form.
How are the theories different? What is the same?
How did life begin on Earth?
The following videos, each about 10 minutes long, give a quick history of the Earth and how life came to be. Please watch the videos and create a quick time line based on the information in the videos for yourself. We will take up the timelines in class to ensure we are all have the same basic information. Please do not worry about the last minute of the The First Humans video, we will discuss this topic later in much more detail.

YouTube Origin Evolution of Life http://www.youtube.com/watch?v=8SgnnV8nV9g&feature=player_detailpage
The First Humans http://www.youtube.com/watch?feature=player_detailpage&v=s-nLJI2BZIM
The following notes are taken from a textbook and are in point form. These notes offer explanations to some of the info found in the videos. We will take a quick look and then start the next section on History of Life.
Chemical evolution is the increase in complexity of chemicals that led to the first cells.
1. Today, we say that "life only comes from life."
2. However, the first cells had to arise from an increased complexity of chemicals.
A. The Early Earth
1. The Earth came into being about 4.6 BYA (BYA).
2. Heat from gravitation and radioactivity formed the Earth in several layers with iron and nickel in a liquid core, silicate minerals in a semi-liquid mantle, and upwellings of volcanic lava forming the first crust.
3. The Earth's mass provides a gravitational field strong enough to hold an atmosphere.
4. Early Earth's atmosphere differed from the current atmosphere, consisting of: a. water vapor, b. nitrogen, c. carbon dioxide, d. small amounts of hydrogen, methane, ammonia, hydrogen sulfide, and carbon monoxide.
5. The early atmosphere was formed by volcanic out-gassing characteristic of the young Earth.
6. The early atmosphere contained little free oxygen (O
2
) and was probably a reducing atmosphere with little free oxygen; a reducing atmosphere lacks free O
2
and allows formation of complex organic molecules.
7. The early Earth was so hot that H
2
O only existed as a vapor in dense, thick clouds.
8. As the Earth cooled, H
2
O vapor condensed to form liquid H
2
O, and rain collected in oceans.
9. The Earth's distance from the sun allows H
2
O to exist in all phases: solid, liquid, and gas.
10. NASA photos seem to confirm that Earth is bombarded by comets adding substantial water vapor.
B. Monomers Evolve
1. Comets and meteorites, perhaps carrying organic chemicals, have pelted the Earth throughout history.
2. A meteorite from Mars (ALH84001) that landed on Earth 13,000 years ago, may have fossilized bacteria.
3. Oparin/Haldane Hypothesis (1920s) a. Oparin/Haldane independently suggested organic molecules could be formed in the presence of outside energy sources using atmospheric gases.

b. Experiments performed by Miller and Urey (1953) showed experimentally that these gases
(methane, ammonia, hydrogen, water) reacted with one another to produce small organic molecules (amino acids, organic acids).
4. Lack of oxidation and decay allowed organic molecules to form a thick, warm organic soup.
5. Ammonia may have been scarce in the early atmosphere; undersea thermal vents, which line ocean ridges, might have been responsible for converting nitrogen to ammonia.
C. Polymers Evolve
1. Newly formed organic molecules polymerized to produce larger molecules. a. Wachtershauser and Huber formed peptides using iron-nickel sulfides under ventlike conditions. b. Such minerals have a charged surface that attracts amino acids and provides electrons so they bond together.
2. Protein-first Hypothesis a. Sidney Fox demonstrated amino acids polymerize abiotically if exposed to dry heat. b. Amino acids collected in shallow puddles along the rocky shore; heat of the sun caused them to form proteinoids (i.e., small polypeptides that have some catalytic properties). c. When proteinoids are returned to water, they form cell-like microspheres composed of protein. d. This assumes DNA genes came after protein enzymes; DNA replication needs protein enzymes.
3. The Clay Hypothesis a. Graham Cairns-Smith suggests that amino acids polymerize in clay, with radioactivity providing energy. b. Clay attracts small organic molecules and contains iron and zinc atoms serving as inorganic catalysts for polypeptide formation. c. Clay collects energy from radioactive decay and discharges it if temperature or humidity changes. d. If RNA nucleotides and amino acids became associated so polypeptides were ordered by and helped synthesize RNA, then polypeptides and RNA arose at the same time.
4. RNA-first Hypothesis a. Only the macromolecule RNA was needed at the beginning to lead to the first cell. b. Thomas Cech and Sidney Altman discovered that RNA can be both a substrate and an enzyme. c. RNA would carry out processes of life associated with DNA (in genes) and protein enzymes. d. Supporters of this hypothesis label this an "RNA world" 4 BYA.
D. A Protocell Evolves
1. Before the first true cell arose, there would have been a protocell or protobiont.
2. A protocell would have a lipid-protein membrane and carry on energy metabolism.
3. Fox showed that if lipids are made available to microspheres, lipids become associated with microspheres producing a lipid-protein membrane.
4. Oparin demonstrated a protocell could have developed from coacervate droplets.

a. Coacervate droplets are complex spherical units that spontaneously form when concentrated mixtures of macromolecules are held in the right temperature, ionic composition, and pH. b. Coacervate droplets absorb and incorporate various substances from the surrounding solution. c. In a liquid environment, phospholipid molecules spontaneously form liposomes, spheres surrounded by a layer of phospholipids; this is called the "membrane-first" hypothesis. d. A protocell could have contained only RNA to function as both genetic material and enzymes.
5. If a protocell was a heterotrophic fermenter living on the organic molecules in the organic soup that was its environment, this would indicate heterotrophs preceded autotrophs. a. A heterotroph is an organism that cannot synthesize organic compounds from inorganic substances and therefore must take in preformed organic compounds. b. An autotroph is an organism that makes organic molecules from inorganic nutrients.
6. If the protocell evolved at hydrothermal vents, it would be chemosynthetic and autotrophs would have preceded heterotrophs.
7. The first protocells may have used preformed ATP, but as supplies dwindled, natural selection would favor cells that could extract energy from carbohydrates to transform ADP to ATP.
8. Since glycolysis is a common metabolic pathway in living things, it evolved early in the history of life.
9. As there was no free O
2
, it is assumed that protocells carried on a form of fermentation.
10. The first protocells had a limited ability to break down organic molecules; it took millions of years for glycolysis to evolve completely.
11. Fox has shown that a microsphere has some catalytic ability; Oparin found that coacervates incorporate enzymes if they are available in the medium.
E. A Self-Replication System Evolves
1. In living systems, information flows from DNA ? RNA ? protein; it is possible that this sequence developed in stages.
2. The RNA-first hypothesis suggests that the first genes and enzymes were RNA molecules. a. These genes would have directed and carried out protein synthesis. b. Ribozymes are RNA that acts as enzymes. c. Some viruses contain RNA genes with a protein enzyme called reverse transcriptase that uses
RNA as a template to form DNA; this could have given rise to the first DNA.
3. The protein-first hypothesis contends that proteins or at least polypeptides were the first to arise. a. Only after the protocell develops complex enzymes could it form nucleic acids from small molecules. b. Because a nucleic acid is complicated, the chance that it arose on its own is minimal. c. Therefore, enzymes are needed to guide the synthesis of nucleotides and then nucleic acids.
4. Cairns-Smith suggests that polypeptides and RNA evolved simultaneously.

a. The first true cell would contain RNA genes that replicated because of the presence of proteins; they become associated in clay in such a way that the polypeptides catalyzed RNA formation. b. This eliminates the chicken-and-egg paradox; both events happen at the same time.
5. Once the protocell was capable of reproduction, it became a true cell and biological evolution began. a. After DNA formed, the genetic code still had to evolve to store information. b. Because the current code is subject to fewer errors than other possible codes, and because it minimizes mutations, it likely underwent a natural selection process.
6. Most biologists suspect life evolved in basic steps. a. Abiotic synthesis of organic molecules such as amino acids occurred in the atmosphere or at hydrothermal vents. b. Monomers joined together to form polymers at seaside rocks or clay, or at vents; the first polymers could have been proteins or RNA or both. c. Polymers aggregated inside a plasma membrane to make a protocell that had limited ability to grow; if it developed in the ocean it was a heterotroph, if at a hydrothermal vent, a chemoautotroph. d. Once the protocell contained DNA genes or RNA molecules, it was a true cell.
Geologists have devised the geological timescale, which divides the history of Earth into eras, and then periods and epochs.
Era Period Years Ago Major Events
Precambrian
Paleozoic
Cambrian
Ordovician
4.5 billion
590 million
505 million
First living cells
Bacteria
Photosynthesis
Algae
First invertebrates
Algae
Marine Invertebrates
Arthropods
Mollusks
First fish
Fungi
Silurian
Devonian
"Age of Fishes"
438 million
408 million
Many fish
Trilobites
Vascular Plants
Plants on Land
Arthropods on Land
Lots o' fishes
First amphibians and insects

Mesozoic
"Age of Reptiles"
Cenozoic
"Age of Mammals"
Carboniferous 360 million
Permian
Triassic
Jurassic
286 million
248 million
213 million
Mosses
Many amphibians
First reptiles
Mass marine extinction
Amphibian decline
Pangaea
First mammals
Dinosaurs
Pangaea begins to separate
Dinosaurs dominate
First birds
Cretaceous
Tertiary
144 million
Flowering plants
Mass extinction
65 million
Birds,mammals, insects flourish
Continents in modern positions
Quaternary
2 million to present
First hominids
Ice Ages
Extinction of giant mammals
(mammoth)
A. Fossils Tell a Story
1. A fossil is the remains or traces of past life, usually preserved in sedimentary rock.
2. Most dead organisms are consumed by scavengers or decompose.
3. Paleontology is the study of fossils and the history of life, ancient climates, and environments.
4. Sedimentation has been going on since the Earth was formed; it is an accumulation of particles forming a stratum, a recognizable layer in a stratigraphic sequence laid down on land or in water.
5. The sequence indicates the age of fossils; a stratum is older than the one above it and younger than the one below it.
B. Relative Dating of Fossils
1. Strata of the same age in England and Russia may have different sediments.
2. However, geologists discovered that strata of the same age contain the same fossils, termed

index fossils.
3. Therefore, fossils can be used for the relative dating of strata.
4. A particular species of fossil ammonite is found over a wide range and for a limited time period; therefore, all strata in the world that contain this ammonite are of the same age.
5. However, relative dating does not establish the absolute age of fossils in years.
C. Absolute Dating of Fossils
1. Absolute dating relies on radioactive dating to determine the actual age of fossils.
2. Radioactive isotopes have a half-life, the time it takes for half of a radioactive isotope to change into a stable element.
3. Carbon 14 (14C) is a radioactive isotope contained within organic matter. a. Half of the carbon 14 (14C) will change to nitrogen 14 (14N) every 5,730 years. b. Comparing 14C radioactivity of a fossil to modern organic matter calculates the age of the fossil. c. After 50,000 years, the 14C radioactivity is so low it cannot be used to measure age accurately.
4. It is possible to determine the ratio of potassium 40 (40K) and argon 40 to date rocks and infer the age of a fossil.
What is Pangea? Continental Drift?
Plate tectonics is the study of the lithosphere, the outer portion of the earth consisting of the crust and part of the upper mantle. The lithosphere is divided into about a dozen large plates which move and interact with one another to create earthquakes, mountain ranges, volcanic activity, ocean trenches and many other features. Continents and ocean basis are moved and changed in shape as a result of these plate movements.

The sequence of maps below show how a large supercontinent, known as Pangaea was fragmented into several pieces, each being part of a mobile plate of the lithosphere. These pieces were to become Earth's current continents. The time sequence show through the maps traces the paths of the continents to their current positions..
In the early 1900's Alfred Wegener proposed the idea of Continental Drift. His ideas centered around continents moving across the face of the earth. The idea was not quite correct - compared to the plate tectonics theory of today - but his thinking was on the proper track. In

addition, a variant spelling of Pangaea is "Pangea". It appears in some textbooks and glossaries, however, Pangaea is the current preferred spelling.
Who was Darwin? What is Evolution?
Some of Darwin’s most important work was done at the Galapagos Islands: http://www.youtube.com/watch?v=TzAvFtQv3oQ&feature=player_detailpage
Darwin’s Arrival http://www.youtube.com/watch?v=KUshLAzXJm4&feature=player_detailpage
The Finches http://www.youtube.com/watch?v=l25MBq8T77w&feature=player_detailpage
1. In 1831, Charles Darwin, a 22-year-old naturalist, accepted a position aboard the ship
HMS Beagle that began a voyage around the world; it provided Darwin with many observations.
2. The pre-Darwinian world-view was different from the post-Darwinian. a. Pre-Darwinian world-view was determined by intractable theological beliefs.
1) The earth is young.
2) Each species was specially created and did not change over time.
3) Variations are imperfections varying from a perfectly-adapted creation.
4) Observations are to substantiate the prevailing worldview. b. Darwin's ideas were part of a larger change in thought already underway among biologists; this concept would eventually be known as evolution.
A. Mid-Eighteenth-Century Contributions
1. Carolus Linnaeus and Taxonomy a. Taxonomy is the science of classifying organisms; taxonomy had been a main concern of biology. b. Carolus Linnaeus (1707-1778) was a Swedish taxonomist.
1) Linnaeus developed a binomial system of nomenclature (two-part names for each species [e.g., Homo sapiens]).
2) He developed a system of classification for all known plants.
3) Like other taxonomists of his time, Linnaeus believed in the ideas of a) special creation-each species had an "ideal" structure and function; and b) fixity of species-each species had a place in the scala naturae, a sequential ladder of life.
2. Georges Louis Leclerc a. Georges Louis Leclerc, known by his title, Count Buffon (1707-1788), was a French naturalist. b. He wrote on the natural history of all known plants and animals, provided evidence of descent with modification. d. His writings speculated on influences of the environment, migration, geographical isolation, and the struggle for existence..
3. Erasmus Darwin a. Erasmus Darwin (1731-1802) was Charles Darwin's grandfather.

b. He was a physician and a naturalist whose writings on both botany and zoology contained many comments that suggested the possibility of common descent. c. He based his conclusions on
1) changes undergone by animals during development,
2) artificial selection by humans
3) the presence of vestigial organs d. Erasmus Darwin offered no mechanism by which evolutionary descent might occur.
B. Late Eighteenth-/Early-Nineteenth Century Contributions
1. Cuvier and Catastrophism a. George Cuvier (1769-1832), a French vertebrate zoologist, was the first to use comparative anatomy to develop a system of classifying animals. b. He founded the science of paleontology-the study of fossils-and suggested that a single fossil bone was all he needed to deduce the entire anatomy of an animal. c. To explain the fossil record, Cuvier proposed that a whole series of catastrophes
(extinctions) and repopulations from other regions had occurred. d. Catastrophism is the term applied to Cuvier's explanation of fossil history: the belief that catastrophic extinctions occurred, after which repopulation of surviving species occurred, giving an appearance of change through time.
2. Lamarck's Acquired Characteristics a. Lamarck (1744-1829) was the first to state that descent with modification occurs and that organisms become adapted to their environments. b. Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's. c. Lamarck mistakenly saw "a desire for perfection" as inherent in all living things. d. Inheritance of acquired characteristics was Lamarck's belief that organisms become adapted to their environment during their lifetime and pass these adaptations to their offspring. e. Experiments fail to uphold Lamarck's inheritance of acquired characteristics;
Darwin's Theory of Evolution
A. Darwin's Background
1. His nature was too sensitive to pursue medicine; he attended divinity school at
Cambridge.
2. He attended biology and geology lectures and was tutored by the Reverend John
Henslow.
3. Henslow arranged his five-year trip on the HMS Beagle; Darwin was an observant student of nature.
B. Geology and Fossils
1. Observed massive geological changes were caused by slow, continuous processes. a. Darwin took Lyell's book, Principles of Geology, on the voyage of the HMS Beagle. b. In contrast to catastrophists, Hutton proposed that the earth was subject to slow but continuous geological processes (e.g., erosion and uplifting) that occur at a uniform rate, a theory called uniformitarianism. c. Fossils of huge sloths and armadillo-like animals suggested modern forms were descended from extinct forms with change over time; therefore species were not fixed.
(glyptodont, mylodon)

C. Biogeography
1. Biogeography is the study of the geographic distribution of life forms on earth.
2. Patagonian hares replaced rabbits in the South American grasslands.
3. The greater rhea found in the north was replaced by the lesser rhea in the south.
4. Comparison of the animals of South America and the Galápagos Islands caused Darwin to conclude that adaptation to the environment can cause diversification, including origin of
new species.
5. The Galápagos Islands a. These volcanic islands off the South American coast had fewer types of organisms. b. Island species varied from the mainland species, and from island-to-island. c. Each island had a variation of tortoise; long and short necked tortoises correlated with different vegetation. d. Darwin's Finches
1) Finches on the Galápagos Islands resembled a mainland finch but there were more types.
2) Galápagos finch species varied by nesting site, beak size, and eating habits.
3) One unusual finch used a twig or thorn to pry out insects, a job normally done by (missing) woodpeckers (Darwin never witnessed this finch behavior).
4) The variation in finches posed questions to Darwin: did they descend from one mainland ancestor or did islands allow isolated populations to evolve independently, and could presentday species have resulted from changes occurring in each isolated population?
D. Natural Selection and Adaptation
1. Darwin decided that adaptations develop over time; he sought a mechanism by which adaptations might arise.
2. Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation.
3. Because the environment is always changing, there is no perfectly-adapted organism.
4. There are three preconditions for natural selection. a. The members of a population have random but heritable variations. b. In a population, many more individuals are produced each generation than the environment can support.

c. Some individuals have adaptive characteristics that enable them to survive and reproduce better.
5. There are two consequences of natural selection. a. An increasing proportion of individuals in succeeding generations will have the adaptive characteristics. b. The result of natural selection is a population adapted to its local environment.
6. Natural selection can only utilize variations that are randomly provided; therefore there is no directedness or anticipation of future needs.
7. Extinction occurs when previous adaptations are no longer suitable to a changed environment.
E. Organisms Have Variations
1. In contrast to the previous worldview where imperfections were to be ignored, variations were essential in natural selection.
2. Darwin suspected, but did not have today's evidence, that the occurrence of variation is completely random.
3. New variations are as likely to be harmful as helpful.
4. Variations that make adaptation possible are those that are passed on from generation to generation.
5. Darwin could not state the cause of variations because genetics was not yet established.
F. Organisms Struggle to Exist
1. Malthus proposed that human populations outgrow food supply and death and famine were inevitable.
2. Darwin applied this to all organisms; resources were not sufficient for all members to survive.
3. Therefore, there is a constant struggle for existence; only certain members survive and reproduce.
G. Organisms Differ in Fitness
1. Organisms whose traits enable them to reproduce to a greater degree have a greater fitness.
2. Darwin noted that humans carry out artificial selection. a. Early humans likely selected wolf variants; produced the varieties of domestic dogs. b. Many crop plant varieties can be traced to a single ancestor. d. Evolution by artificial or natural selection occurs when more fit organisms reproduce and leave more offspring
H. Organisms Become Adapted
1. An adaptation is a trait that helps an organism be more suited to its environment.
2. Unrelated organisms living in the same environment often display similar characteristics.
3. Because of differential reproduction, adaptive traits increase in each succeeding generation.
I. On the Origin of Species by Darwin
1. After the HMS Beagle returned to England in 1836, Darwin waited over 20 years to publish.
2. He used the time to test his hypothesis that life forms arose by descent from a common ancestor and that natural selection is a mechanism by which species can change and new species arise.

3. Darwin was forced to publish Origin of Species after reading a similar hypothesis by
Alfred Russel Wallace.
Is there Evidence of Evolution?
A. Fossils Evidence
1. The fossil record is the history of life recorded by remains from the past.
2. Fossils include skeletons, shells, seeds, insects trapped in amber, and imprints of leaves.
3. Transitional forms reveal links between groups. a. Archeopteryx is an intermediate between reptiles and birds. b. Eustheopteron is an amphibious fish. c. Seymouria is a reptile-like amphibian. d. Therapsids were mammal-like reptiles.
4. The fossil record allows us to trace the history of the modern-day horse Equus.\B.
Biogeographical Evidence
1. Biogeography studies the distribution of plants and animals worldwide.
2. Distribution of organisms is explained by related forms evolving in one locale and spreading to other accessible areas. a. Darwin observed South America had no rabbits; he concluded rabbits originated elsewhere. b. Biogeography explains the abundance of finch species on the Galápagos Islands lacking on the mainland.

3. Physical factors, such as the location of continents, determine where a population can spread. a. Marsupials arose when South America, Antarctica, and Australia were joined; Australia separated before placental mammals arose, so only marsupials diversified in Australia.
C. Anatomical Evidence
1. Organisms have anatomical similarities when they are closely related because of common descent. a. Homologous structures in different organisms are inherited from a common ancestor. b. Analogous structures are inherited from unique ancestors and have come to resemble each other because they serve a similar function. c. Vertebrate forelimbs contain the same sets of bones organized in similar ways, despite their dissimilar functions.
2. Vestigial structures are remains of a structure that was functional in some ancestors but is no longer functional in the organism in question. a. Most birds have well-developed wings; some bird species have reduced wings and do not fly. b. Humans have a tailbone but no tail.
See also Whale Evolution

3. Embryological development a. During development, all vertebrates have a post-anal tail and paired pharyngeal pouches.
1) In fishes and amphibian larvae, the pouches become gills.
2) In humans, the pouches becomes the middle ear; tonsils, and glands
E. Biochemical Evidence
1. Almost all living organisms use the same basic biochemical molecules, e.g., DNA, ATP, enzymes.
2. Organisms utilize the same DNA triplet code and the same 20 amino acids in their proteins.
3. These similarities can be explained by descent from a common ancestor.
4. Life's vast diversity has come about by only a slight difference in the same genes.
F. Because it is supported by so many lines of evidence, evolution is no longer considered a hypothesis.
1. Evolution is one of the great unifying theories of biology, similar in status to the germ theory of disease in medicine.
2. In science, a theory is supported by a large number of observations or a large amount of experimental evidence
G. Pace of Evolution
1. Phyletic gradualism - slow process with many transitional forms
2. Punctuated equilibrium - speciation occurs rapidly, transitional links not evident, explains lack of fossils
3. Living fossils (horseshoe crab, coelacanth) support punctuated equilibrium

Population Genetics and Evolution
1. It was not until the 1930s that population geneticists were able to apply the principles of genetics to populations and thus to recognize when evolution had occurred.
2. A population is all of the members of a single species occupying a certain area at the same time.
3. Evolution that occurs within a population is called microevolution.
4. Population genetics studies the variation in alleles in a gene pool.
5. The gene pool is the total of all the alleles in a population; it is described in terms of gene frequencies.
6. Industrial Melanism a. The case of the peppered moths provides a case study in a shift in phenotype frequencies under selection. b. With birds acting as a selective agent, the light colored moths were reduced while darkcolored moths were better adapted to survive on the darkened trees
Please note that according to The Hardy–Weinberg principle both the allele and the genotype frequencies in a population remain constant—that is, they are in equilibrium—from generation to generation unless specific disturbing influences are introduced. Those disturbing influences include non-random mating , mutations , selection , limited population size, "overlapping generations", random genetic drift , gene flow and meiotic drive . It is important to understand that outside the lab, one or more of these "disturbing influences" are always in effect. That is,
Hardy–Weinberg equilibrium is impossible in nature. Genetic equilibrium is an ideal state that provides a baseline against which to measure change.
( http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle )
A. Causes of Microevolution
1. Genetic Mutations a. Many traits in organisms are polymorphic, i.e., two or more distinct phenotypes are present in the population due to mutated genes. b. Analysis of Drosophila enzymes indicates they have multiple alleles at least at 30% of their gene loci. c. In humans, freckles are an example of polymorphism, as are the ABO blood types. d. Mutations can be beneficial, neutral, or harmful; a seemingly harmful mutation that requires
Daphnia to live at higher temperatures becomes advantageous when the environment changes.
B. Gene Flow
1. Gene flow (gene migration) is the movement of alleles among populations by migration of breeding individuals.
2. Gene flow can increase variation within a population by introducing novel alleles
3. Continued gene flow decreases diversity among populations, causing gene pools to become similar.
4. Gene flow among populations can prevent speciation from occurring.

C. Nonrandom Mating
1. Random mating involves individuals pairing by chance, not according to genotype or phenotype.
2. Nonrandom mating involves inbreeding and assortative mating.
3. Inbreeding is mating between relatives to a greater extent than by chance. a. Inbreeding does not change the allele frequencies. b. However, inbreeding decreases the proportion of heterozygotes. c. In human populations, inbreeding increases the frequency of recessive abnormalities.
4. Assortative mating occurs when individuals mate with those that have the same phenotype.
5. Sexual selection occurs when males compete for the right to reproduce and the female selects males of a particular phenotype. (guppies, lions)
D. Genetic Drift
1. Genetic drift refers to changes in allele frequencies of a gene pool due to chance, more often in small populations
2. Genetic drift occurs when founders start a new population, or after a genetic bottleneck with interbreeding. a. The bottleneck effect prevents most genotypes from participating in production of the next generation.
1) The bottleneck effect is caused by a severe reduction in population size due to a natural disaster, predation, or habitat reduction.
2) The bottleneck effect causes a severe reduction in the total genetic diversity of the original gene pool.
3) The cheetah bottleneck causes relative infertility because alleles were lost due to intense inbreeding when populations were reduced in earlier times.

b. The founder effect is an example of genetic drift where rare alleles or combinations occur in higher frequency in a population isolated from the general population.
1) This is due to founding individuals containing a fraction of total genetic diversity of the original population.
2) Which particular alleles are carried by the founders is dictated by chance alone.
3) As an example, dwarfism is much higher in a Pennsylvania Amish community due to a few
German founders.
Natural Selection - the process that results in adaptation of a population to the environment.
1. Natural selection requires a. variation (i.e., the members of a population differ from one another), b. inheritance (i.e., many of the differences between individuals in a population are heritable genetic differences), c. differential adaptedness (i.e., some differences affect how well an organism is adapted to its environment), and d. differential reproduction (i.e., better adapted individuals are more likely to reproduce).
2. Fitness is the extent to which an individual contributes fertile offspring to the next generation.
3. Relative fitness compares the fitness of one phenotype to another.
A. Types of Selection.
1. Directional selection occurs when an extreme phenotype is favored; the distribution curve shifts that direction. a. A shift to dark-colored peppered moths from light-colored correlated with increasing pollution. b. Drug-resistant strains of bacteria are a serious health threat and represent this type of selection. c. Increases in insecticide-resistant mosquitoes and resistance of the malaria protozoan
Plasmodium to medications are also examples of directional selection. d. The gradual increase in the size of the modern horse, Equus, correlates with a change in the environment from forest-like conditions to grassland conditions.
2. Stabilizing selection occurs when extreme phenotypes are eliminated and the intermediate phenotype is favored. a. The average number of eggs laid by Swiss starlings is four or five. b. If the female lays more or less than this number, fewer survive. c. Genes determining the physiology of yolk production and behavior are involved in clutch size.
3. Disruptive selection occurs when extreme phenotypes are favored and can lead to more than one distinct form. a. British snails (Cepaea nemoralis) vary because a wide range causes natural selection to vary. b. In forest areas, thrushes feed on snails with light bands. c. In low-vegetation areas, thrushes feed on snails with dark shells that lack light bands.

B. Maintenance of Variations
1. Populations always show some genotypic variation; populations that lack variation may not be able to adapt to new conditions.
2. The following forces promote genetic variation. a. Mutation creates new alleles and genetic recombination still combines these alleles. b. Gene flow among small populations introduces new alleles. c. Natural selection, such as disruptive selection, itself sometimes promotes variation.
3. Sickle-Cell Disease a. In sickle-cell disease, heterozygotes are more fit in malaria areas because the sickle-cell trait does not express unless the oxygen content of the environment is low; but the malaria agent causes red blood cells to die when it infects them (loss of potassium). b. Some homozygous dominants are maintained in the population but they die at an early age from sickle-cell disease. c. Some homozygotes are maintained in the population for normal red blood cells, but they are vulnerable to malaria.
Macroevolution
Macroevolution refers to any evolutionary change at or above the species level.
Speciation is the splitting of one species into two or more species or the transformation of one species into a new species over time; speciation is the final result of changes in gene pool allele and genotypic frequencies.
A. What is a Species?
1. Linnaeus separated species based on morphology, i.e., their traits differed; Darwin saw that similar species are related by common descent.
2. Ernst Mayr (1942) developed the biological species concept: a species is a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups.
3. The biological definition of a species says that the members of one species interbreed and have a shared gene pool, and each species is reproductively isolated from every other species.
4. Gene flow occurs between populations of one species but not between populations of different species.
5. Biochemical genetics uses DNA hybridization techniques to determine relatedness of organisms; the phylogenetic species concept uses DNA/DNA comparisons.

B. Reproductive Isolating Mechanisms
1. For two species to be separate, gene flow must not occur between them.
2. A reproductive isolating mechanism is any structural, functional, or behavioral characteristic that prevents successful reproduction from occurring.
3. Prezygotic ("before formation of a zygote") isolating mechanisms are anatomical or behavioral differences between the members of two species that prevent mating or make it unlikely fertilization will take place if mating occurs. a. Habitat isolation occurs when two species occupy different habitats, even within the same geographic range, so that they are less likely to meet and to attempt to reproduce. b. Temporal isolation occurs when two species live in the same location, but each reproduces at a different time of year, and so they do not attempt to mate. c. Behavioral isolation results from differences in mating behavior between two species. d. Mechanical isolation is the result of differences between two species in reproductive structures or other body parts, so that mating is prevented. e. Gamete isolation includes incompatibility of gametes of two different species so they cannot fuse to form a zygote; an egg may have receptors only for the sperm of its own species or a plant stigma prevents completion of pollination.
4. Postzygotic ("after formation of a zygote") isolating mechanisms prevent development of a hybrid after mating has taken place. a. Zygote mortality is when hybrids (offspring of parents of two different species) do not live to reproduce. b. Hybrid sterility occurs when the hybrid offspring are sterile (e.g., mules). c. In F2 fitness, the offspring are fertile but the F2 generation is sterile.
C. Modes of Speciation
1. Allopatric speciation occurs when new species result from populations being separated by a geographical barrier that prevents their members from reproducing with each other. a. First proposed by Ernst Mayr of Harvard University. b. While geographically isolated, variations accumulate until the populations are reproductively isolated. c. First postzygotic isolation occurs, then prezygotic reproductive isolation occurs.
2. Sympatric speciation would occur when members of a single population develop a genetic difference (e.g., chromosome number) that prevents them from reproducing with the parent type. a. The main example of sympatric speciation is in plants. b. Failure to reduce chromosome number produces polyploid plants that reproduce successfully only with polyploids. c. Backcrosses with diploids are sterile.

D. Adaptive Radiation
1. Adaptive radiation is a rapid development from a single ancestral species of many new species.
2. The case of Darwin's finches illustrates the adaptive radiation of 13 species from one founder mainland finch.
3. On the Hawaiian Islands, a wide variety of honeycreepers descended from one goldfinchlike ancestor; Hawaii is also the home of the silversword plants that radiated from ancestral tarweeds.
How has the human population evolved? What will the future hold?
YouTube – Evolution of Modern Humans http://www.youtube.com/watch?v=_KjJ234XPC4&feature=player_detailpage
Scientists Claimthe evolution of man http://www.youtube.com/watch?v=F7SlnVngFjg&feature=player_detailpage http://www.wisegeek.com/what-is-creation-theory.htm
http://geology.com/pangea.htm