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Speciation

Speciation. What’s a species ? A group of organisms that normally interbreed in nature to produce fertile offspring What’s speciation ? The formation of a new species How does speciation happen?. Step 1- Geographic isolation A population of a species becomes physically separated

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Speciation

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  1. Speciation What’s a species? A group of organisms that normally interbreed in nature to produce fertile offspring What’s speciation? The formation of a new species How does speciation happen?...

  2. Step 1- Geographic isolation A population of a species becomes physically separated (E.g. by a lake or mountain).

  3. Step 2- Natural selection Each population changes over many generations through natural selection and mutation. This results in subspecies populations that have their own different characteristics but can still interbreed.

  4. Step 3- Reproductive isolation The populations change sufficiently for them to no longer be able to interbreed. ->A new species has been produced (speciation).

  5. What changes might cause reproductive isolation? • Change in colour patterns • Change in mating habits • Seasonal differences in mating times • Changed chromosome that prevents sperm of one group from fertilising eggs of another mates no longer recognised

  6. Types of evolution • Speciation shows us how new species might arise from a common ancestor. • Different evolutionary paths have been suggested: • Divergent evolution • Convergent evolution • Parallel evolution

  7. Divergent evolution • Divergent evolution is when new forms of a species evolve from a common ancestor E.g. The Galapagos Island finches or the geographically isolated rabbits • Results in phenomenon known as adaptive radiation where ancestral organisms become adapted to their new environment and evolve into new forms suited to the environment • Figure 3.2.8 What environment would have resulted in the whale? The bat?

  8. Convergent evolution • Convergent evolution or convergence occurs when organisms evolve and develop similar adaptations due to: • Living in similar environments and habitats • Having similar lifestyles and food source • Similar habitats -> similar characteristics selected for -> organisms that look similar despite having very different genes passed down from very different ancestors • These organisms may have analogous structures, specific body parts that are similar looking. • Figure 3.2.10

  9. Parallel evolution • Parallel evolution occurs where related species evolve similar features while separated from each other • E.g. Old World monkeys and New World monkeys share many features because of their common ancestors, apart from their very different tails

  10. To summarise • Divergent = common ancestry, different environments, different organisms • Convergent = no common ancestry, similar environments, similar organisms • Parallel = common ancestry, different environments, similar organisms

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