Transcript Evolution
EVOLUTION PART I “H OW SCIENTIFIC THEORIES ARE DEVELOPED , H ISTORY, AND MAJOR CONTRIBUTORS ” 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. H UTTON 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 H UTTON 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 H UTTON 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. C HARLES D ARWIN 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 C HARLES D ARWIN 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! C HARLES D ARWIN 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 C HARLES D ARWIN One of the observations that spawned Darwin’s 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! I MPORTANT V OCABULARY 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”) An example would be the selection for a mate that birds go through I MPORTANT V OCABULARY Adaptation – any inherited characteristic that increases and organism’s 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, it’s 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) I MPORTANT V OCABULARY 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. G ENES AND V ARIATION 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 G ENES AND V ARIATION Natural Selection and trait distribution Directional selection is when individuals in a population have a higher fitness over those in the middle range or lower range 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 N ATURAL S ELECTION IN P OPULATIONS 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 variation within the population D IRECTIONAL S ELECTION Directional selection is the effect of a shift in a population’s phenotype in response to natural selection towards a more favored phenotype from the variation within the original population D ISRUPTIVE S ELECTION Disruptive selection Occurs when both extreme phenotypes are favored by natural selection while the mean population is selected against by something in nature S TABILIZING S ELECTION 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 EVOLUTION PART II E XPLANATIONS FOR E VOLUTION Catastrophism states that natural disasters like floods and earthquakes have happened during Earth’s 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 E XPLANATIONS FOR E VOLUTION Uniformitarianism Geologic processes that shape the earth are uniform through time and can be seen by look at rock strata like an ancient “yearbook” E XPLANATIONS FOR E VOLUTION 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 E VIDENCE FOR E VOLUTION 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! E VIDENCE FOR E VOLUTION 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 E VIDENCE FOR E VOLUTION N ATURAL S ELECTION 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 N ATURAL S ELECTION 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 M ECHANISMS OF E VOLUTION 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 M ECHANISMS OF E VOLUTION Bottleneck effect occurs after an event greatly reduces the size of a population such as over hunting or a meteor from outer space! M ECHANISMS OF E VOLUTION 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 E VOLUTION 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 frequency E VOLUTION PART III S PECIATION THROUGH I SOLATION 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 R EPRODUCTIVE I SOLATION 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 B EHAVIORAL I SOLATION 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 G EOGRAPHIC I SOLATION 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 T EMPORAL I SOLATION 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 E VOLUTION 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 E VOLUTION 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 C ONVERGENT E VOLUTION 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) D IVERGENT E VOLUTION 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 S PECIES E VOLUTION 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 S PECIES C OEVOLUTION 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! S PECIES E XTINCTION 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 A DAPTIVE R ADIATION 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. G EOLOGIC T IME 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 G EOLOGIC T IME 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 R ADIOMETRIC D ATING S PECIES C LASSIFICATION BASED UPON E VOLUTIONARY R ELATIONSHIPS 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