Transcript adaptation
Mechanisms for Evolution After the voyage… Darwin observed that all individuals struggled… Predation Competition for: • Food • Space • Mates • shelter Finding mates Food Shelter Predators Space Darwin observed… Overproduction Genetic Variation Within populations, individuals have different traits Struggle to survive More offspring produced than can survive Must compete for existence Differential reproduction Not everyone has an equal opportunity to reproduce. Those with best adaptations are most likely to survive and reproduce “Descent with Modification” species – living and extinct – descended through reproduction from preexisting species (genetic information passed down from generation to generation) Every A species must be able to change over time (modify) in response to the changes in their environment How Natural Selection works… In any population, individuals have traits, many of which show variation. Traits that are determined by genes are heritable. Advantageous traits benefit an organism and allow it to leave more offspring—this is natural selection. Advantageous traits become more common in a population, resulting in adaptation of the species in response to its environment. What is an adaptation? An adaptation is a structural(physical) change in DNA or behavior that helps a living thing survive and reproduce in its environment. Examples: The shape of a bird’s beak or the color of an animal’s fur. Types of Adaptations STRUCTURAL (physical) Mimicry Camouflage Protective Coloration BEHAVIORAL • • Hibernation Move in groups PHYSIOLOGICAL Changes in metabolic processes ie. Pesticide-resistance in insects Examples of Adaptations The shape of an animal’s teeth is related to its diet. Herbivores, such as deer, have many molars for chewing tough grass and plants. Carnivores, such as lions, have sharp canines to kill and tear meat. Animal Defense Some animals use these methods of defense to protect themselves: Camouflage Blend with environment Mimicry Look like other species Bright colors • warning “Hair” projections • Cause harm/ pain Adaptation Applications: Lions Why are the eyes of a lion set in front of the head rather than on the sides? Answer: Eyes in front of the head allow for depth perception and ability to judge distances when hunting. Adaptation Applications: Giraffe How are their long necks adapted to their lifestyle? Answer: The extra length is thought to have evolved to help the giraffe spot predators and other giraffes in the distance. Interestingly, giraffes and humans have the same number of vertebrate in their necks. How are plants adapted to their environment? Each biomes plant adaptations This cactus displays In the autumn, desert adaptations: it has deciduous trees drop spines rather than leaves their leaves to and it stores water in its minimize water loss. stem. In floating plants, chlorophyll is restricted to the upper surface. Note the green color on the top of the leaves and the reddish underside. Soft stems enable prairie grasses to bend in the wind. Narrow leaves minimize water loss. How are adaptations & evolution related? Adaptations allow the species to change over time – a process we call evolution. From the variation present in the population, the variant selected for depends on the selective pressures that the species encounters in its environment. What is a selective pressure? A driving force of evolution and natural selection, ANY force that shapes/changes organisms within a given environment is a SELECTIVE PRESSURE. Can be caused by: mutation, natural selection, genetic drift Possible selective pressures: available prey/food; predators; environmental stress; competition w/ others Some basic definitions to understand a theory… Fact: an observation that has been repeatedly confirmed Law: a general description about how the physical world behaves Hypothesis: a testable statement that can be used to build inferences and explanations All contribute to… Theory: a well-substantiated explanation that incorporates facts, laws, inferences and tested hypotheses. In science, you don’t get any better than a theory. What is evolution? Let’s start by seeing what evolution is not. Old Theories of Evolution Things change because organisms want or need them to! Jean Baptiste Lamarck (early 1800’s) “The inheritance of acquired characteristics” What does this Mean? According to Lamarck: A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves. The animal’s increasingly long neck was passed on to its offspring. So…what IS evolution? A basic definition… “…evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next." - Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974 What does this mean? Evolution is a change in the number of times specific genes that code for specific characteristics occur within an interbreeding population. Individuals don’t evolve, populations do! Types of Evolution Divergent Evolution Many species evolve from a common ancestor. Populations change as they adapt to different environmental conditions, eventually resulting in new species. Convergent Evolution Fast swimmers such as tuna (a fish), penguin (a bird), and seal (a mammal) all have streamlined bodies. They evolved independently but made similar adaptations in form to perform the same function of moving through water. Similar adaptations among unrelated organisms to similar environments is called convergent evolution. These honeycreepers, evolved from a single ancestral species that lived on the Hawaiian Islands long ago. When an ancestral species evolves into a group of species to fit a number of diverse habitats, the result is called ADAPTIVE RADIATION. Adaptive radiation is a type of divergent evolution, which occurs when populations change as they adapt to different environmental conditions, eventually resulting in new species. Adaptation Games Animal Adaptations Game Harcourt animal adaptation game