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Speciation and Phylogenetic Trees Mrs. Dignan’s Biology Class Darwin’s 4 Points 1. Organisms can produce more offspring than they can support. 2. Any environment has a finite supply of resources. 3. Individuals have natural variation in their traits, due to mutations and genetic recombination. 4. Those individuals most suited to their environment tend to survive and pass on their traits. Macroevolution vs. Microevolution Microevolution= “small change”= changes within a species Macroevolution= “large change”= changes that produce new species What is a species? A group of organisms that can reproduce and produce viable, fertile offspring Where do new species come from? All new species come from existing species Speciation – when 1 species becomes 2 Speciation happens in 3 steps: Isolation between 2 populations Random Mutation Natural Selection of the traits that are best suited to the new environment Step 1: Isolation In order the evolve into 2 separate species, there must be no breeding between 2 populations. Isolation can happen in 5 basic ways: Geographic Behavioral Mechanical Ecological Post-zygotic A) Geographic Isolation A physical geographic barrier (mountains, continents, bodies of water, etc.) separates populations and prevents gene flow. Example- Cichlids in African rift lakes B) Behavioral Isolation The two populations do not mate with each other because they exhibit different mating behaviors. C) Mechanical Isolation Two populations are separated because their bodies do not “fit” together right, preventing gene flow. D) Ecological Isolation The populations become isolated from one another because they have different functions and habitats within the ecosystem. E) Post-zygotic Isolation Even if 2 individuals do mate, they may be too genetically different to produce viable offspring. The egg may not be fertilized The zygote may die The resulting offspring may be sterile Speciation – 1 species becomes 2 The process of making new species happens in 3 steps: Isolation Mutation Natural Selection Phylogenetic Trees Phylogenetic trees: tools that biologists use to show evolutionary relationships between species. Phylogenetic Trees