Understanding Evolution: The Theory of Natural Selection, Slides of Biology

Download Understanding Evolution: The Theory of Natural Selection and more Slides Biology in PDF only on Docsity! Evolution – How Change Occurs Docsity.com Some things to keep in mind BEFORE we study evolution...the nature of SCIENCE. • What is SCIENCE? – A process that seeks to find natural explanations for observations of the natural world – Science cannot comment on anything that is outside the realm of the physical/natural. • Philosophy • Ethics / morality • Religion – Nor do philosophy, etc. operate in the terms of science. Religion, philosophy, etc. are valuable tools designed to help people answer MANY important (perhaps THE MOST important) questions, but NOT scientific questions. • Questions like – why is the sky blue, – how do bacteria cause disease, – How do cells become cancerous? – How can we kill cancer cells?... are answerable by science… questions like: “What’s the meaning of life?” are NOT. Docsity.com What are the of rules of science? • Rule 2: Science is TESTABLE – Scientific questions must be TESTABLE and that means the you can make observations either through experimentation or some other means to test whether a hypothesis is wrong. – Ideas of religion, morality, philosophy CANNOT be “tested” with experiments or observations and are not meant to be. – For example, The whole point of religion is that it is based on faith, NOT whether a hypothesis was “accepted” or “rejected” based on “evidence”. Docsity.com What are the of rules of science? • Rule 3: Science can be WRONG! – Scientific process is designed to correct itself – If a scientific idea is found to be wrong or partially wrong, the whole point of science is for evidence to be presented to fix the idea – If evidence arises to disprove an idea, the idea will be either modified to fit the new evidence or it will be discarded all together. – Generally, faith/religion cannot be wrong in the eyes of those who believe. Docsity.com Other Things to Keep in Mind before we study Evolution... Theory vs. Hypothesis • It’s called the THEORY of Evolution – what does this mean?? • THEORY vs. HYPOTHESIS Docsity.com So, what exactly IS evolution? • Evolution = the kinds of organisms on Earth have changed over time – This is observable. It is not hypothesis or theory, but fact. – Best evidence is fossil record, which we will talk about later… • Natural Selection is the theory part… – This is the WAY (mechanism) by which evolution occurs – Fact: Fossil record shows that over time life on Earth has changed – Theory: Natural selection explains how life on Earth has changed. Docsity.com Note that neither evolution nor natural selection is a… • Guess • Opinion • Hypothesis • The vast majority of scientists agree that the evidence points to natural selection as the mechanism that causes evolution to happen. – This is well supported by lots of research, over long periods of time, by lots of people ---- that is, it’s a THEORY. – In science a theory is a BIG DEAL • Other theories: – Cell theory – Newton’s theory of gravitation – Copernicus – Earth moves around the sun Docsity.com Where did the idea of evolution come from? • Not from Charles Darwin • The idea of Evolution has been around for a very long time – Aristotle (Greeks) • Darwin is just the one who told us the MECHANISM by which evolution could occur Docsity.com HMS Beagle • It was Darwin’s job to hike the coast of S. America wherever the Beagle stopped. • He made notes describing land forms, etc. • He collected LOTS of specimens – Living and fossils – Many never before seen by Europeans Docsity.com Voyage of the HMS Beagle • Stopped in Galapagos Islands – 500 miles off coast of Ecuador Docsity.com Galapagos Islands ETA r aa Cee) POE Cnr) Isabela PACIFIC OCEAN GALAPAGOS & bail YN] B Sy Genovesa iu Marchena Etec - « North Seymour iy Bett) cio @ Baltra , South Plaza ey Docsity.com But what he found was many different kinds of finches Darwin was amazed to find out: All 13 species of birds were finches… Sparrow? But there is only one species of finch on the mainland! Warbler Finch Small Ground Finch Large Ground Finch Did one species of finches become many different species? If so, how? Woodpecker Finch Docsity.com Example – Darwin’s Finches • Darwin found several different species of finch on the Galapagos Islands • Each species was specifically adapted to feed in the particular habitat in which it lived • Each was at least somewhat similar to the others AND to a finch commonly found on the S. American mainland • Why? Docsity.com Example: Darwin’s Finches • Darwin suggested that the solution to this puzzle that made the most sense was that the original mainland ancestor colonized one of the islands many years ago • It’s descendents slowly became adapted to the various food sources available on the many different island habitats Docsity.com Anti-Darwin Cartoon from 1800s Docsity.com Why was Darwin so hated by some? • Some people felt that Darwin’s ideas challenged their religious beliefs – Some felt that Darwin’s ideas implied there was no God – Some felt that Darwin’s ideas meant that there was no moral imperative for people to “do good” • In reality, Darwin made no judgments about God or religion in his work and did not see why his work had to be at odds with religion. Docsity.com What exactly did Darwin say? • Organisms overreproduce – make more babies that the environment can possibly support. Docsity.com What exactly did Darwin say? • This variation must be INHERITABLE to be important in natural selection because you must be able to pass it on to offspring. Docsity.com What exactly did Darwin say? • Organisms that are better suited to their environment will outcompete those that are less well suited. • Over lots of time, the less well-suited organisms will “lose out” to the better suited ones. Docsity.com What exactly did Darwin say? • The “winning competitors” will survive and pass on their traits to their offspring more often than the “losing competitors” Docsity.com Remember What Natural Selection Says… • Over lots of time, the less well-suited organisms will “lose out” to the better suited ones. • Over lots of time, the species will come to possess the “good” characteristics possessed by the “winning competitor”. • Over lots and LOTS of time, many such small “improvements” may accumulate and alter the species in such a major way that a new species is created. – SPECIATION – creation of a new species Docsity.com Darwin and Artificial Selection • Artificial Selection – Choosing organisms with certain traits and breeding them • In this case the human is the “selector” instead of the environment, but the principle of section is the same. – Can lead to organisms that look VERY different from the originals in just a relatively few generations Docsity.com Docsity.com Examples of Natural Selection – The Peppered Moths • At the beginning of the 19th century (before the industrial revolution), most of the tree trunks in England were light in color • So were most of the Peppered Moths • Camouflage – hard for predators to find them. Docsity.com Examples of Natural Selection – The Peppered Moths • However, a few darker Peppered Moths would also appear occasionally in the population. • These did not blend so well on the light trees • No camo = LUNCH for birdies! Docsity.com Light and Dark Peppered Moths BEFORE the Industrial Revolution Docsity.com Examples of Natural Selection – The Peppered Moths • Over just a few generations, the dark moth became the prevailing type found in England. • Does this mean the light moths no longer existed? • What might happen if the pollution were cleaned up?? Docsity.com What is the source for the variation we see in the moths (or any other organisms)? • GENES • Remember that variation does NOT occur because an organism “wants” or “needs” to “evolve”. • Variation just happens (RANDOM) – WHY? – Because MUTATION just happens – Because crazy new combinations of genes just happen when organisms sexually reproduce. • Sexual Recombination Docsity.com The Spread of Genes among Organisms (or the decline of genes among organisms…) • Scientists do NOT study individuals when they study evolutionary change. – A mutation occurring in ONE individual does not mean that an evolutionary change has occurred. – A mutation in ONE individual does not mean a new species has occurred • Scientists study POPULATIONS – Collection of individuals of the same species in a given area. The members of a population can breed with each other. Docsity.com Species and Evolutionary Change • What exactly is a species? – Species – A group of similar-looking, though not identical organisms that breed with one another and produce fertile offspring in the natural environment (not the zoo). Docsity.com Species and Evolutionary Change • Because members of a species (population) can breed with each other, they share a common gene pool. • Because of that, when a genetic change occurs in an individual, it can spread through the population as that individual and its offspring mate with other individuals. • IF that gene INCREASES FITNESS, it will eventually be found in MANY individuals in the population (species?) Docsity.com Speciation • When new species evolve from old ones Docsity.com Speciation • If the populations remain separated for a long time, their gene pools beomce so different that their reproductive isolation becomes PERMANENT. • They are now not just separate populations, but separate species. Docsity.com Darwin’s Finches ees Ue tl cri Pr ecires EPrmireta Tis our = ree Darwin’s Finches Leaves Se Darwin's Finches aa Fruit - ADAPTIVE RADIATION pe 7 ad “ ae Grubs i - | ee ie ya Tool Using Finch a, AP il ® Docsity.com Analogous Structures • Structures that are similar in appearance and function, but do NOT share a common origin • Bird wing and butterfly wing Docsity.com Gradualism • Says evolutionary change occurs slowly/gradually • Darwin’s original idea Docsity.com Modifications to Darwin’s idea of Gradualism • Environmental change can cause evolution to go faster • More evolutionary change after a mass extinction – Lots of habitat, niches to fill • Punctuated equilibrium – A more modern modification of Darwin’s original idea – Long stable periods interrupted by brief periods of rapid change Docsity.com