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Evolution Darwin and Natural Selection Charles Darwin On the Origin of Species Sailed with the HMS Beagle Observations made in the Galapagos Islands These observations helped him form the theory of how species change What is Natural Selection? Within every species or population, there is diversity (variation). Organisms with variations that are favorable survive and pass their genes onto their offspring. The next generation has the favorable variations. Types of Adaptations Protective Coloring – Camouflage – Mimicry Physiological Adaptations – Reproductive Changes – Other changes Behavioral Adaptations – Using tools Evidence for Evolution Fossil record Anatomy – Homologous structures – Analogous structures Vestigial structures Embryology Molecular biology (DNA differences) Evidence for Evolution A. The fossil record 1. Geological time scale - major events 2. The history of the Earth is divided into Eons, Eras, Periods , and Epochs. 3. Think…….Jurassic Park 4. Radioactive Isotopes are used to find the age of rocks. Darwin’s Evidence for Evolution Fossils ossils – Extinct species resemble living ones for same region – Species found in successive layers of rock show progressive changes in characteristics Darwin’s Evidence for Evolution Geographical Distribution – Distant regions with similar climates have unrelated plants/animals – Plants/animals of a region or continent are distinctive, and many/all are often related to a single group Darwin’s Evidence for Evolution Oceanic Islands – Although islands generally have few species, those they have are often unique and show relatedness to one another – Species on islands often show relatedness to nearest continent, and not to species on similar islands in other oceans Darwin’s Evidence for Evolution Artificial selection – Plant and animal breeders – Breeders select who survives/breeds next generation – Many widely different breeds/cultivars produced from same original stocks – Could nature act similarly? Darwin Influenced by Others Malthus – “Essay of the Principle of Population” (1798) – Populations of plants/animals can increase geometrically – Populations of plants/animals remain relatively constant – Death limits populations Darwin hypothesized natural selection as a means by which selective survival of individuals with superior attributes gradually changes the average characters of the population as a whole over many generations B. Evidence from Comparative Anatomy – Comparative Anatomy- the study of structural similarities and differences between living things • 1. Homologous Structures- parts of different organisms that have similar structure, but different forms and functions – human arm and hand, whale flipper, cat leg, bat wing, bird wing • 2. Analogous Structures- parts of different organisms that have similar forms and functions, but different internal structure (example: wing of a bird, wing of an insect) • 3. Vestigial Structures- remnants of structures that were once functional in an ancestral form » -appendix, wisdom teeth, coccyx (tailbone) Homologous Structures- same structure: different function Analogous structures Insect wing QuickTime™ and a decompressor are needed to see this picture. Bird Wing QuickTime™ and a decompressor are needed to see this picture. C. Comparative Embryology – Structurally different species show common patterns in embryological development • presence of gill slits, 2-chambered hearts, tails • the longer the embryos show similarities, the more closely related the species D. Evidence from DNA – - Each individual organism has its own specific DNA structure (DNA fingerprint) – The closer the structure of DNA between organisms (species), the closer the evolutionary relationship What is a Population? Population:groups of interbreeding individuals that live in the same place at the same time Populations evolve over many generations, individuals don’t Individuals in a population compete for resources with each other How Does Evolution Work? Populations produce more offspring than the environment can support The unequal ability of individuals to survive and reproduce leads to the gradual change in a population over many generations Mechanism for change in a population of organisms Animals who have greater fitness survive in environment and live to reproduce Random changes (mutations) can lead to greater or less fitness Adaptations allow an organism to survive better in their environment Adaptations Can arise in response to environmental pressures – Temperature – Antibiotic resistance in bacteria – Pesticide resistance – Morphological changes in peppered moths Types of Selection Directional – Extreme form favored by natural selection Stabilizing – Middle form most successful Disruptive – Two extreme forms successful in separate environments Stabilizing Selection Disruptive Selection Directional Selection How fast does evolution occur? Gradualism – Darwin – Species change slowly over time Punctuated Equilibrium – Steven Jay Gould – Species can make rapid “leaps” in evolution Modern Synthesis – Parts of both are correct Types of Evolution • Convergent Evolution • Species may resemble each other but not be related - happens when environment selects for phenotypes (sharks and dolphins) • Divergent Evolution • Two or more related populations becoming more and more different - response to differing habitats Adaptive radiation is one type Darwin’s Finches are an example How do you define a species? Species: a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions. - Biological Species Concept: Ernst Mayr Speciation -making new species or adaptive radiation Go to: http://evolution.berkeley.edu/evosite/evo101/VADefining Species.shtml How are new species created? •Geographic Isolation physical separation of members of a population •Change in chromosome number •Polyploidy in plants •Adaptive Radiation What is Biodiversity? - The diversity of living things on this planet. "In a Darwinian sense," Professor E.O. Wilson wrote, "the organism does not live for itself. Its primary function is not even to reproduce other organisms; it reproduces genes, and it serves as their temporary carrier.” All the living things on this planet contribute to the Biodiversity of Earth. Biodiversity studies determine endangered species and endangered habitats.