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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
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?...

slide2

Step 1- Geographic isolation

A population of a species becomes physically separated

(E.g. by a lake or mountain).

slide3

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.

slide4

Step 3- Reproductive isolation

The populations change sufficiently for them to no longer be able to interbreed.

->A new species has been produced (speciation).

what changes might cause reproductive isolation
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

types of evolution
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
divergent evolution
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?
convergent evolution
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
parallel evolution
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
to summarise
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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