EVOLUTION PART I HOW SCIENTIFIC THEORIES ARE DEVELOPED, HISTORY, AND MAJOR CONTRIBUTORS The process of change over time SCIENTIFIC THEORIES A scientific theory is a concept that has been well tested, and is accepted as an explanation to a wide range of observations. SCIENTIFIC THEORIES
The scientific method uses objective experimentation to predict, verify, or refute, an assertion made by a theory. Based on the results of the experiment(s), the theory is modified. The processes involved with prediction, observation, verification (or refuting) are repeated, continually testing and modifying the theory until the theory fits all possible experimental observations. SCIENTIFIC THEORIES & THE THEORY OF
EVOLUTION According to most scientists, all life on Earth has a common ancestor. In order to produce the immense amount of difference among all living organisms, certain ones had to evolve into distinct species. This differentiation occurred through evolution.
Populations of organisms developed different traits, through mechanisms such as mutation. Those with traits that were more beneficial to survival were naturally selected for survival; hence the term natural selection. SCIENTIFIC THEORIES & THE THEORY OF EVOLUTION The theory of evolution through natural selection provides a scientific explanation for the history of life on earth as depicted in the fossil record and in the similarities evident within the diversity of existing organisms.
HUTTON AND LYELL Sir Charles Lyell provided conclusive evidence for the theory of uniformitarianism (gradualism) which had been developed originally by the late 18th century Scottish geologist, James Hutton. Hutton Lyell HUTTON AND LYELL Lyell documented the fact that the earth must be very old and that it has been subject to the same sort of natural processes in the past that operate today in shaping the land.
These forces include erosion, earthquakes, glacial movements, volcanoes, and even decomposition of plants and animals. the HUTTON AND LYELL This held that the natural forces now changing the shape of the earth's surface have been operating in the past much the same way.
In other words, This revolutionary idea was instrumental in leading Charles Darwin to his understanding of biological evolution in the 1830's. the present is the key to understanding the past. CHARLES DARWIN Darwin is considered as the father of evolution
Losing his passion to become a doctor in med school he took to the sea to become a naturalist in 1831 The name of the ship he spent 5 years on was the Beagle Darwin returned to England in 1836 with pages of notes from what he saw as well as many specimens from his journey CHARLES DARWIN
Darwin spent 36 days on the Galapagos Islands These islands are located West of the Northern part of South America off the coast of Ecuador The Galapagos islands were an undisturbed island chain void of humans for thousands of years
What Darwin found astonished him! CHARLES DARWIN Because of geographic isolation, the inhabitants of the Galapagos evolved without predators This allowed humans to get as close as they wanted to research the animals
Many species were the same species he found on other continents but, they had key differences! For example, a species of cacti normally only 5 feet tall grew to heights of 20 feet! And lizards swam and ate algae from the rocks CHARLES DARWIN One of the observations that spawned Darwins curiosity was the amazing
similarities between animals of different species! Darwin also noticed that plants and animals had unique characteristics within the same species as well! IMPORTANT VOCABULARY Natural variation is defined as differences among individuals of the same species
Interspecific variation is variation among individuals of the same species Intraspecific variation variation among individuals of different species Artificial selection artificial selection is similar to selective breeding (being chosen) IMPORTANT VOCABULARY Adaptation any inherited characteristic that increases and organisms chance of survival
Adaptations can be a physical characteristic or a more complex behavior This lizard is known as the Thorny Devil and it lives in the harsh outback of Australia where there is very little water To get water, its body has special channels that lead water to the corners of its mouth and all it has to do is gulp to draw the moisture from the air that has condensed on its body (via capillary action) IMPORTANT VOCABULARY
Natural selection aka. Survival of the fittest is defined as nature selecting individuals with characteristics making them well suited to their environment Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species fitness in its environment. GENES AND VARIATION A group of interbreeding individuals is known as a population
The genome of an individual organism is all of the genes that organism possesses worldwide The gene pool is ALL of the genes in a population including all of the possible alleles For example: in Basenji puppies they can have 1 of 4 coat colors The relative frequency is how often that gene
occurs in the gene pool GENES AND VARIATION Natural Selection and trait distribution Directional selection is when individuals in population have a higher fitness over those the middle range or lower range a in This causes a shift in the fitness towards one particular
phenotype As an example: Suppose that there were many different height giraffes in a region of Africa that underwent sever climatic change The food availability is now 8 higher than before and only a limited number of giraffe can actually reach the resource This would be directional selection NATURAL SELECTION IN POPULATIONS
In any population of organisms there is variation within the species There are organisms that fit into a bell curve whereby the largest percent of the population is in the center with slightly different variations on either side These are two bell curves shown above. The mean is the average and the majority of the population phenotype. The curve
represents the entire DIRECTIONAL SELECTION Directional selection is the effect of a shift in a populations phenotype in response to natural selection towards a more favored phenotype from the variation within the original population DISRUPTIVE SELECTION Disruptive selection
Occurs when both extreme phenotypes are favored by natural selection while the mean population is selected against by something in nature STABILIZING SELECTION Stabilizing selection Occurs when the mean phenotype is highly favored in the environment and becomes even more dominant in the population This can lead to a lower diversity which makes species susceptible to disease or other limiting factors
EVOLUTIO N PART II Explanations for Evolution, Natural Selection, Evidence for Evolution, and mechanisms of Evolution EXPLANATIONS FOR EVOLUTION Catastrophism states that natural disasters like floods and earthquakes have happened during Earths long history and that they have caused species extinction in some cases
Gradualism Canyons carved by rivers are examples of gradual changes over time altering the landscape EXPLANATIONS FOR EVOLUTION Uniformitarianism Geologic processes that shape the earth are uniform through time and can be seen by look at rock strata like an ancient yearbook EXPLANATIONS FOR EVOLUTION
Fossils ! Traces of organisms that lived in the past After deposition into the Earth some specimens are preserved and their bones, over a long period of time, become mineralized into a rock-like substance we call fossils EVIDENCE FOR EVOLUTION Charles Darwin saw evidence for evolution in his travels that convinced him that life must have evolved over time
Fossils Darwin found fossils that closely resembled living counterparts Geography as Darwin traveled from island to island he noticed similar species with different adaptations depending on food sources Biogeography- is the study of different organisms and their relatedness around the world Embryology comparison of embryos between similar species shows closely similar traits! EVIDENCE FOR
EVOLUTION Anatomy some of Darwin's best evidence came from the comparison of the body parts of different species Homologous structures are features that are similar in structure but appear in different organisms and often have different functions Analogous structures structures that perform a similar function but are not similar in origin Vestigial structures remnants of organs or
structures that had a function in an early ancestor EVIDENCE FOR EVOLUTION NATURAL SELECTION One of the accepted definitions for natural selection is: the mechanism by which individuals that have inherited, beneficial adaptations produce more offspring (on average) than do other individuals Darwin was comparing the rates of reproduction in
nature to that of human reproduction according to Malthus and concluded: variation within a population must be the answer to success in population growth Four Main Principles of Natural Selection: Variation heritable differences exist in all populations and natural selection acts on those traits present in the environment Overproduction having many offspring results in competition
for resources and promotes natural selection Adaptation the better adapted individuals in any population live longer and pass their successful genes to their offspring Descent with modification over time, natural selection will result in species with adaptations that make them well suited for survival and reproduction in that particular environment NATURAL SELECTION MAIN IDEA
Natural selection acts on phenotypes rather than on the genetic material itself. New alleles are not made by natural selection they occur by natural selection. Natural selection can act only on traits that exist in a population! Fitness The measure of the ability to survive long enough to produce successful offspring The key is to have your offspring survive long enough to have their own offspring MECHANISMS OF EVOLUTION
Natural selection is not the only mechanism by which populations evolve Gene flow the movement of alleles between populations Genetic drift a change in allele frequencies due to chance Bottleneck effect genetic drift that occurs after an even greatly reduces the size of a population
Founder effect genetic drift that occurs after a small number of individuals colonize a new area MECHANISMS OF EVOLUTION Bottleneck effect occurs after an event greatly reduces the size of a population such as over hunting or a meteor from outer space! MECHANISMS OF EVOLUTION
Random mutations occur in populations that may provide a new allele that is advantageous or not. Changes in allele frequency are due to genetic drift FACTORS IN EVOLUTION Genetic drift allele frequencies change due to chance Gene flow movement of alleles from one population to another
Mutation new alleles form through mutation Sexual selection certain traits improve mating success and increase in EVOLUTION PART III Speciation through Isolation, Patterns in Evolution, Fossil record, Geologic Time, and Cladistics SPECIATION THROUGH ISOLATION
Main Idea: New species can arise when populations are isolated Isolation if gene flow between species stops for any reason, the populations are isolated Speciation is the rise of two or more species from one existing species Four types of Isolation: Reproductive isolation
Behavioral isolation Geographic isolation Temporal isolation REPRODUCTIVE ISOLATION Reproductive isolation occurs when members of different populations are no longer able to mate successfully with each other
Two cases: Not physically able to mate They cannot produce offspring able to survive Reproductive isolation between populations is the final step in speciation BEHAVIORAL ISOLATION
A large part of the mating process involves rituals, chemical signals, songs, and courtship dances Behavioral isolation occurs when members of a population are not accepted because of their behavior or improper courtship rituals Example the flashing patterns in male and female fireflies Example the courtship song and dance of the lyre bird in South Australia
GEOGRAPHIC ISOLATION In geographic isolation there are physical barriers that divide a population into two or more groups Rivers, mountains, dried lake beds, or man-made barriers When populations are separated long enough, they may evolve different adaptations and undergo speciation TEMPORAL ISOLATION
A temporal barrier is one that prevents reproduction because of timing Bird migrations are often governed by changing of the seasons and food availability for their young PATTERNS IN EVOLUTION As new species arise they are under pressure to survive. Adaptive traits are kept in a population through natural selection but, sudden changes in an environment can eliminate one or more species
In science, the terms chance and random refer to how easily an outcome can be predicted Mutation and genetic drift cannot be predicted so they are considered random events PATTERNS IN EVOLUTION Natural selection, which acts on diversity, is not random. Individuals with traits that adapt them to their environment better have a better chance of surviving and passing on those adaptations to future generations.
It is important to remember that it is the environment that controls the direction of natural selection CONVERGENT EVOLUTION Different species around the world adapt to similar environments When evolution towards similar traits in unrelated organisms develops it is called convergent evolution The habitat will favor those best adapted for survival (natural selection)
DIVERGENT EVOLUTION When closely related species evolve in different directions, they become increasingly different through divergent evolution As time passed in different habitats, several species of primates evolved from a common ancestor SPECIES EVOLUTION Main Idea: Species can shape each other over time
As species interact they form relationships Close species interaction is called symbiosis As species compete, cooperate, and interact in various ways their evolutionary paths may become connected Two types of these interactions: Coevolution the process by which two or more species evolve in response to changes in the other
Evolutionary arms race a type of coevolution where species respond to other species they are competing with Often times this occurs in predator-prey relationships where the prey evolves to escape the evolving predator as the predator evolves to better catch its prey SPECIES COEVOLUTION One such relationship in nature is between ants and aphids Ants prefer nectar and herd the aphids like sheep to the most succulent parts of a plant for the
aphids to eat The aphids produce a nectar from their abdomen which the ants love! In return for the nectar, the ants protect the aphids from their most feared predator the ladybug! SPECIES EXTINCTION Extinction the elimination of a species from the Earth
Background extinctions extinctions that occur continuously at a very low rate caused by many reasons Mass extinctions sudden, rare events that cause hundreds, thousands, and sometimes millions of species to become extinct ADAPTIVE RADIATION As one species diversifies into many
descendent species it is called adaptive radiation This type of speciation usually follows a mass extinction and creates a Huge diversity of species in a relatively short period of time The diagram shows a Species A that moves to an island displaying the founder effect and Species A undergoes adaptive radiation inhabiting a range of islands and habitats. GEOLOGIC TIME Scientific evidence shows us that the Earth is
about 4.5 billion years old! There are many tools scientists use to discover this Index fossils are fossils of organisms that existed only during a specific time period The trilobite to the right is one of the most abundant fossils during the Paleozoic Era GEOLOGIC TIME
There are a couple methods for determining the age of fossils Relative dating gives you an estimate of the time period of an organism based upon the rock layer in which it is found This method is not very accurate for exact measurements Radiometric dating uses isotopes of organic elements to determine a fairly exact age of a substance relative to the decay of the organic elements found in a sample (usually Carbon-14) This is accurate to a few hundred years or less
RADIOMETRIC DATING SPECIES CLASSIFICATION BASED UPON EVOLUTIONARY RELATIONSHIPS As we look at animals it is apparent that similar animals have a lot in common Example: modern dogs and wolves share a common ancestor The phylogeny of a species is the evolutionary history of that species
The most common way to make an evolutionary tree is through cladistics which is a classification based on common ancestry
Zoos. Aquaria. Wildlife reserves. Purpose of captive breeding. To prevent extinction of endangered species. Conserve species that may not survive well in the wild. Reintroduce animals back into the wild and preserve biodiversity
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