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Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology 4 STEPS TO NATURAL SELECTION Overproduction Competition Variation Evolution through Natural Selection of Genes and Adaptation to the Environment 1- More individuals will be born than will survive and reproduce. (OVERPRODUCTION) ( Meaning that there aren’t enough resources like food, shelter, water, or mates for everyone) 2 – Because there aren’t enough resources for all to survive and reproduce, there will be competition between individuals for resources and mates. (COMPETITION) 3 – There is Genetic Variation among individuals in a species. Some of these genetic differences will help (or hurt) their owners as they compete for resources or mates. (VARIATION) Selection and 4 – On average, individuals with better combinations of genes (genes that help them Adaptation survive in their habitat better) will survive and reproduce more often. Helpful genes will spread through the species over many generations. Other genes will become less common. (NATURAL SELECTION or ADAPTATION) Adaptations (This means that as the good genes are passed on, the population changes to better fit their habitat- these changes are called adaptations, characteristics that help a species fit their environment. For example camels have long eyelashes that keep sand out of their eyes and nostrils that they can close tightly to keep sand out of their nose and keep from drying out – adaptations to living in a desert.) evolution As natural selection continues, whole species can change in form. If a population of a species changes enough, it can become a whole new species. This is evolution- the change in form of an entire species as it adapts to a changing environment. Summarize What four things must happen for natural selection to occur? That is the difference between natural selection and evolution? (hint: how many organisms are does selection work on at a time, what about evolution?) Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology EVIDENCE FOR NATURAL SELECTION AND EVOLUTION EVIDENCE TYPE 1 - ARTIFICIAL SELECTION Artificial Selection, Selective Breeding Artificial Selection, or Selective Breeding is when humans, rather than nature, choose which organisms and genes they want to become more common. Examples are all of the livestock and dog breeds, plus nearly every food that we eat. Why artificial selection helps support the idea of evolution by natural selection. Artificial selection happens when humans allow only organisms that show specific genetic traits to breed. (for example, dairy farmers have chosen their breeding stock from animals with genes for high milk production, high fat content to the milk, strong frames, high udders, etc.) Artificial selection by selective breeding was an important evidence for natural selection because people were already familiar with the idea. They had experienced changes in species, made through selective breeding programs, in their farm and domestic animals, and in many of the plants that they grew, both for food and in their gardens. This made the idea easy to accept. The Fossil Record EVIDENCE TYPE THE FOSSIL RECORD Fossil Fossils are the preserved remains, or evidence, of organisms that lived long ago. Organisms can be petrified (replaced by stone) Different types of fossils trapped in amber (hardened tree sap) Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology Leave behind trace fossils or like tracks or tunnels molds (a print in the rock where the organism was) More Fossil Types Sometimes we find preserved remains, when cold dryness or acid, keep bacteria from decomposing them. In this case, what you are finding are the actual remains of the organism, preserved in acid, ice, or by drying out. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology Fossils show changes in species and groups of species over time. Transitional fossils are very important, because they show intermediate forms, Transitional forms species that have characteristics of both older groups and newer ones. This is a fossil of Archaeoptyrix a small dinosaur that had feathers like a bird, but few other bird characteristics. It is a transitional form between dinosaurs and birds showing the early evolution of the group. Fossils also show that many species have become extinct as environments change. The fossils show that as species go extinct they are replaced by others that are better adapted to the environment. Why the fossil record supports the theory of Evolution Fossils give important evidence of evolution because they make clear that species both change and can go extinct over time. Fossils also provide us with transitional forms that show species such as feathered birds and whales with legs, that are in between older and newer forms. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology EVIDENCE TYPE 3 - Homologous structures Homologous structures are parts of organisms that are made from the same body parts (muscles bones, scales etc.), but have become adapted for different uses. Homologous Structures Are made from the same Homologous structures show how adaptation and evolution change a body to fit Body parts but do different different habitats. This is because they show how the same bones, muscles, skin, and jobs (e.g. a bird wing and a organs have evolved to serve different purposes in different groups of species. human arm). (The most commonly used example is the arm of a human, the front leg of a horse, the fin of a fish, the flipper of a whale and the wing of a bat. All of these are made using the same bones and muscles. But depending on their habitat, the bones, and the muscles surrounding them have changed to fit the species’ environment and niche. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology Another good example of homologous structures are the many different forms leaves take in plants.) How homologous structures support the theory of evolution. Homologous structures support the theory of evolution because they show that the same body parts can be adapted to take many different forms depending on the environment. The flipper of a whale serves it much better in the water than an arm and hand would. So as the ancestors of whales spent more and more time in the water, their front legs evolved into flippers (do a search on “whale transitional forms” for more info. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology EVIDENCE TYPE 4 - Analagous Structures Analogs are things that are made of different parts, but do the same job, like an hourglass, a sundial and a watch. Analagous structures Analagous structures are body parts that do the same thing, but are made up of different parts. One of the best example comes from flying animals, Bats, birds and insects all have wings, but they are made of different structures. Bird Analogous structures are made from different wings are arms, bat wings are hands and insect wings don’t even have bones. body parts, but do the same job. Analogous structures are important because they show that, given the same evolutionary pressures (or opportunities), similar structures can evolve to fit the purpose – even when using different body parts to do it. (In this case wings evolved to give different groups the advantages an animal gets by being able to glide or fly through the air.) Another example would be all of the different body parts that have evolved to push an animal through water – the flukes of a whale, the tail fin of a fish, the webbed feet of a duck, the body of a snake, even the wings of a penguin, all are parts adapted to let an animal move through water to find food. Natural selection chose body parts that were better shaped to move through water and slowly those parts evolved into new shapes and forms – for example from a bird wing to a penguin’s flipper. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology EVIDENCE TYPE 6 – DNA AND GENETICS You can look at DNA sequences in different species and compare them to see how closely related they are. Species that are closely related have nearly identical spellings of genes. Also you can look at genes that are in many different groups of species and compare the DNA sequence of the genes to see what groups are related to each other. You can look at the changes in the gene and figure out its history by the changes in the spelling of the gene. Steve Symeonides 4/18/2012 Period 1,4,6,7 Biology