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Evolution and Natural Selection How life has changed on Earth. The Theory of Evolution •Evolution is the gradual change in a species over a long period of time. •The evolution of a species is the result of an individual organism struggling to survive in a given environment. •A scientific theory is a wellsupported testable explanation of phenomena that have occurred in the natural world •There has been no credible evidence presented to disprove evolution The Theory of Evolution •Individuals with the best traits or adaptations will have the best chance to survive. •The individuals that survive then have the chance to reproduce and pass those traits to their offspring. The Theory of Evolution •Charles Darwin was the first person to successfully describe the process of evolution, which he titled, “Natural Selection” •Darwin traveled the world on the H.M.S. Beagle. •He made observations about the different types of life he found on the different continents and remote islands. •During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. •That hypothesis has become the theory of evolution. •Darwin collected the preserved remains of ancient organisms, called fossils. •Some of those fossils resembled organisms that were still alive. •Others looked completely unlike any creature he had ever seen. Natural Selection •Darwin’s Theory of Natural Selection is broken down into a few main ideas. –Overproduction –Variation –Competition –Selection Natural Selection •Overproduction- Individuals of a species will have more babies than will be able to survive. –Insects will produce hundreds of babies each year –Fish will lay hundreds of eggs –Birds will lay a few eggs –Mammals will produce many babies each year Natural Selection •Variation- Each of the babies that are produced by the parents will be a little bit different genetically. –There will be slight changes in size, color, speed, development, etc. Natural Selection •Competition- each individual that is produced wants to survive. It will compete with its own species and other species to survive. –Finding food and water –Avoiding predators –Attracting mates –Obtaining shelter or a territory Natural Selection •Selection- The individuals with the best traits will survive and have the opportunity to pass on its traits to its offspring. •Evolution occurs when these good traits build in the population over many generations and the bad traits are eliminated by the death of the individuals. •Darwin noted that plant and animal breeders would breed only the largest hogs, the fastest horses, or the cows that produced the most milk. •Darwin termed this process artificial selection. •Artificial selection is the selection by humans for breeding of useful traits from the natural variation among different organisms. •Common in dogs, bird species, live stock (pigs, cows, horses), and plant species The Struggle for Existence •Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources. •The struggle for existence means that members of each species compete regularly to obtain food, living space, and other necessities of life. •The ability of an individual to survive and reproduce in its specific environment is fitness. •Darwin proposed that fitness is the result of adaptations. •An adaptation is any inherited characteristic that increases an organism's chance of survival. •Successful adaptations enable organisms to become better suited to their environment and better able to survive and reproduce. •Individuals with characteristics that are not well suited to their environment either die or leave few offspring. •Darwin called this process survival of the fittest. •Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection. •The traits being selected contribute to an organism's fitness in its environment. •Over time, individuals with a greater fitness will survive and reproduce at a higher rate that individuals with inferior traits or behaviors. • This results in more individuals with an better fitness to build in the population. •Some types of adaptations are camouflage, blending into the environment so the creature is not seen. Stick Mantid Flower Mantid •Mimicry- evolved to look like another creature that is much more dangerous. Coral Snake (Poisonous) Milk Snake (Not poisonous) Descent With Modification •Each living species has descended, with changes, from other species over time. •Darwin referred to this principle as descent with modification. •Descent with modification implies that all living organisms are related to one another. •This is the principle known as common descent. –An individuals ability to survive and reproduce in a given environment is its •evolution. •fitness. •camoflague. •Artificial selection – Which of the following is not a part of Darwin’s idea of natural selection •Individuals within the population is genetically different •Individuals within the population must compete for resources to survive •A population produces more offspring than can survive •The weak and unhealthy should have an equal chance to survive –When humans select which traits are beneficial in another species like dogs, horses, and pigs is called •Natural selection •Artificial selection •Fitness •Mimicry –Darwin theorized that all species are related to each other, they just evolved differently over time. This idea is called •Convergent evolution •Artificial selection •Common descent •Acquired characteristics – Which of the statements below would be consistent with Darwin’s ideas of evolution? •Evolution attempts to develop perfect species that will survive for all time •Populations evolve better with less variation •Evolution is a rapid process that happens in a short amount of time •Individuals with better adaptations survive and reproduce at higher rates Evidence for Evolution •Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development, or embryology. The Fossil Record •Darwin saw fossils as a record of the history of life on Earth. •By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time. Archaeopteryx Biogeography •Organisms are uniquely adapted to the environments or habitats in which they live. •The same types of organisms evolve independently based on the environmental pressure of their habitat. Biogeography in fossils Homologous Body Structures •Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures. •Similarities and differences in homologous structures help biologists group animals according to how recently they last shared a common ancestor. • Not all homologous structures serve important functions. • The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species. • These organs are called vestigial organs. Embryology •The early stages, or embryos, of many animals with backbones are very similar. •The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. 1 2 3 4 5 6 7 Which embryo is the human, Cat, chick, rabbit, fish, salamander, pig, and tortoise? 8 Biochemical Evidence •Almost all living organisms use the same basic biochemical molecules for life. –DNA (genetic material) –ATP (cellular energy source) –Enzymes (proteins to control chemical reactions. •Many similarities found in the genes and DNA sequences of completely different organisms. •Human DNA and chimpanzee DNA is 98.77% identical in their base pairing. •Human DNA is more similar to other mammals than it is to reptiles, birds or fish. •Biologists compare the amino acid sequences of common proteins in different life forms. •Similarities in amino acids is consistent with the idea of common descent by evolutionary theory. Similarities in Hemoglobin, protein in blood cells Similarities in Cytochrome c, protein found in the mitochondria. Helps in energy production –The body parts found in different species that have the same basic structure are •Homologous structures. •Vestigial organs. •Caused by random chance. •Shows evidence that each species are not related to each other –To show how the bones and body designs of species have evolved over the ages, scientists study •DNA and RNA •The rock layers in the Earth •The fossils of the different species •Only modern living species – Which are used to show evidence that supports the theory that species have evolved over time I. Fossils II. Embryos III. DNA of different species • • • • I only I and III only I and II only I, II and III Summary of Darwin's Theory • Individual organisms differ, and some of this variation is heritable. • Organisms produce more offspring than can survive, and many that do survive do not reproduce. • Because more organisms are produced than can survive, they compete for limited resources. •Individuals best suited to their environment survive and reproduce most successfully. •These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. •This process of natural selection causes species to change over time. •Species alive today are descended with modification from ancestral species that lived in the distant past. •This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life. Where does the variation come from? •Each individual has its own set of instructions on how to build the creature (DNA). Where does the variation come from? •DNA is made of individual genes (small sections of DNA that are the instructions for a specific part of the body or protein) •If DNA was a recipe book, a gene would be a recipe. •Many genes have at least two forms, or alleles. •Genetic variation is studied in populations. •A population is a group of individuals of the same species that interbreed. •A gene pool consists of all genes, including all the different alleles, that are present in a population. •The relative frequency of an allele is the number of times the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. •Relative frequency is often expressed as a percentage. •In genetic terms, evolution is any change in the relative frequency of alleles in a population. •The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction. Mutations are RANDOM changes in the DNA that can cause changes in the genes (instructions to build the body) Where does the variation come from? •Most mutations have no effect on the individual or are harmful. •A small number of mutations might be beneficial to the organism. Where does the variation come from? •If the mutation results in a change to a body part that helps the creature to survive and then reproduce, the change would be called an Adaptation. •Mutations can only change or alter existing traits, they do not create new traits. Where does the variation come from? •During the process of sexual reproduction, one set of DNA comes from each parent (in the sperm and eggs) to create an new unique set of instructions or combination of genes. Where does the variation come from? •Each time the sperm and eggs are made, the instructions are altered slightly to allow for variations or slight differences. •This way, siblings will always have slightly different combinations of genes, even though they have the same parents. Importance of Variation •Variation is essential for the continued survival of life on the planet. •Living things adapt to changes in the environment. •This environmental pressure is what helps to determine a creature’s fitness. •If the environmental conditions change, variations between individuals and between species helps to ensure that some will have beneficial traits. •Even alleles that were harmful in one environment, may become beneficial in the changing environment. •Alleles that cause a rabbit to have larger than normal ears that lives in the snow is at a disadvantage. It loses too much heat. •But if the environment changes, warming the air, the larger ears are beneficial to keep the rabbit cooler. •Some environmental changes may be so severe, that whole species die off, goes extinct. •By having variation between the different species allows for the possibility that some of the species survive and repopulate the environment. •When dinosaurs went extinct, a few small mammals and small reptiles survived to repopulate the environment. •Natural selection affects which individuals survive and reproduce and which do not. •If an individual dies without reproducing, it does not contribute its alleles to the population’s gene pool. •If an individual produces many offspring, its alleles stay in the gene pool and may increase in frequency. •Peppered moths live on the trees found in England. •There are two main alleles for peppered moths –White –Black •The trees the moths would live on had white bark. •Birds catch moths they can see. •Which moth was best adapted? Which allele would have the highest frequency in the population? White Allele •Over time, pollution stained the bark of the trees, making them dark. •Which allele has the advantage? •What happened the frequency of the dark allele? •The trait or adaptation that enables an organism to be successful is a function of its phenotype, physical characteristics. •Evolution only selects which phenotypes are favorable. •The phenotype is determined by the genotype, alleles found in the genes. •The genotypes of beneficial phenotypes build in the gene pool, change the gene frequency. •Individuals with poor phenotypes, thick black fur in a desert environment, will not be as successful in passing on their genotypes. •The alleles for harmful traits will reduce in frequency in the gene pool, but will not disappear. •Even alleles that are lethal, cause death, are not completely eliminated from the gene pool. •A homozygous recessive (aa) genotype may be lethal, killing the individual early in life, like TaySachs disorder. •But a recessive allele can still be passed down generation after generation in heterozygous genotypes (Aa) •Sickle cell anemia is a homozygous recessive disorder, but the allele continues to be passed down in heterozygous individuals that have a normal phenotype. •Normal blood cells are round, fitting easily through blood vessels. •Sickle cells, get stuck in smaller blood vessels, causing infections Normal phenotype Sickle cell phenotype •Evolution is any change over time in the relative frequencies of alleles in a population. •Populations, not individual organisms, can evolve over time. •For example, a lizard population is normally brown, but has mutations that produce red and black forms. •Red lizards are more visible to predators, so they will be less likely to survive and reproduce. Therefore, the allele for red color will become rare. •Black lizards may warm up faster on cold days. This may give them energy to avoid predators better than even the brown lizards. In turn, they may produce more offspring. •The allele for black color will increase in relative frequency. •Black and red are both changes in phenotype –Natural selection causes •The frequency of alleles to remain the same •An individual to evolve to a new environment. •the change in a species due to changes in the gene pool •The population to remain unchanging for as long as possible –The amount of alleles for a specific trait found in the gene pool is the •The frequency of alleles •Genetic drift •Common descent •Gene flow –Which statement is true regarding mutations •Mutations have no effect on the frequency of alleles •Most mutations have no effect on an individual •Mutations are unable to change the gene pool •No mutations can be beneficial to an individual. Genetic Drift •A random change in allele frequency is called genetic drift. •In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. •Over time, a series of chance occurrences of this type can cause an allele to become common in a population. •Genetic drift may occur when a small group of individuals colonizes a new habitat. •Individuals may carry alleles in different relative frequencies than did the larger population from which they came. •The new population will be genetically different from the parent population. •Descendants Population A Population B Founders Effect •When allele frequencies change due to migration of a small subgroup of a population it is known as the founder effect. • Some remote villages, polydactyl is common because the trait was in founding members. Bottleneck effect •When allele frequencies change due to the random removal of alleles in the gene pool is the bottleneck effect. Variation leads to Speciation •Since each individual in a species is attempting to survive (not be killed), they develop different ways to survive based on their adaptations. •As different adaptations build in a population, it leads to the development of new species. •This is Speciation •A species is a group of organisms that breed with one another and produce fertile offspring. •The gene pools of two populations must become separated for them to become new species. •As new species evolve, populations become reproductively isolated from each other. •When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred. •Reproductive isolation can develop in a variety of ways, including: •behavioral isolation •geographic isolation •temporal isolation •Behavioral isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. Blue-footed boobies display their blue feet when courting potential mates. Red-footed boobies are not impressed by the display. •Geographic isolation occurs when two populations are separated by geographic barriers such as rivers or mountains. •Geographic barriers do not guarantee the formation of new species. •If two formerly separated populations can still interbreed, they remain a single species. •Potential geographic barriers may separate certain types of organisms but not others. •Temporal isolation occurs when two or more species reproduce at different times or seasons. –When two species do not reproduce because of differences in mating rituals, the situation is referred to as •temporal isolation. •geographic isolation. •behavioral isolation. •reproductive isolation. – Lethal diseases continue to be passed on through the population generation after generation because the alleles •Are mutations and don’t affect most individuals. •Are dominant and easy for an individual to avoid. •Because they are passed on only by homozygous individuals. •Can be passed on by heterzygous individuals, since they don’t suffer from the trait. –The most important factor involved in the evolution of the different species that reproduce during different times of the year is •temporal isolation. •geographic isolation. •behavioral isolation. •different food sources. –All of the following played a role in speciation of Galápagos finches EXCEPT •natural selection. •Geographic isolation. •reproductive isolation. •no changes in the gene pool. –When a new species evolves because members of the population be breading during differnet seasons, is an example of •Geographic isoltion. •Genetic isolation. •Behavioral isolation. •Reproductive isolation. Diversity of Life •Evolution and speciation has produced the vast diversity seen on Earth. •Life originated on Earth 3.8 Billion Years Ago. •The first life forms were Bacteria, simple single celled creatures. •Bacteria were the only living things for more than 2 billion years Diversity of Life •These cells evolved into more complex multicellular cells, the first animals and plants. Diversity of Life •Over the ages, life evolved into many new species as the environment changed. •Evidence of these ancient forms of life are found in Fossils. •Fossils are any remains of living things that were trapped in the Earth and kept from decomposing. (Bones, teeth, footprints, dung, amber) What Fossils Tell •Most fossils are found in sedimentary rock. •Sedimentary rock is layers of dirt, small rocks and other materials, that are smashed together for long periods of time until the fuse. What Fossils Tell •If an animal or plant is trapped in these layers of dirt and rock, their bodies may be preserved and turned into a fossil. •As more layers of dirt pile up above, sedimentary rock forms distinct layers. •The deeper a fossil is in the rock, the older it is. •The higher it is in the rock, the younger it is. •Determining the age of a fossil by looking at what rock layer it is in is Relative dating. •Relative dating does not give an exact age of the fossil, only determines if it is older than or younger than another fossil. •To determine the actual age of a fossil, Absolute dating is used. •Absolute dating measures the amount of radioactive atoms found in the fossil or layer of rock the fossil is in. •Scientists are then able to determine the actual age of the rock. Rates of Decay Parent Uranium 238 Lead 206 Half- life (years) 4.5 Billion Uranium 235 Lead 207 704 Million Potassium 40 Argon 40 1.25 Billion Carbon 14 Daughter Nitrogen 14 5730 years Diversity Helps Survival •Fossils show the great diversity of life from the past. •It was through this great diversity that has allowed life to continue even after mass extinctions. Mass Extinctions •Mass extinctions are when a large number of species die off from the planet, never to return. •The Permian mass extinction resulted in 90%-95% of all marine species and 70% of terrestrial species to go extinct •The Cretaceous extinction caused 18% of terrestrial vertebrates to go extinct (including dinosaurs) Mass Extinctions •Most mass extinctions are caused by dramatic changes in the environment. •The greater the diversity of life, the better the chance that some life forms will survive the change and adapt to the changing environment. – Which is correct that it allows life to continue when there is a dramatic change to the environment •A greater amount of biodiversity in the environment •A larger population with less variation •A smaller amount of biodiversity but with a large population size •A lower frequency of alleles in the gene pool – Which best describes genetic drift •When the frequency of alleles changes because of natural selection •When the frequency of alleles changes because of random chance •When there is a large amount of sexual reproduction •A lower frequency of alleles due to mutations – A scientist determines that a mass extinction occurred in the past. Which type of evidence would support this hypothesis? •Many fossils of the same species found in the same layers of sedimentary rock •Many fossils of a variety of different species found in the same layers of sedimentary rock •The same type of fossil found in many different layers of sedimentary rock •Mass extinctions can not be determined by fossils