हिंदी

Natural Selection and Speciation

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Estimated time: 5 minutes
CBSE: Class 12

Key Points: Natural Selection and Speciation

1. Mutations & Speciation - Mutations in microbes lead to new phenotypes; over several generations, this can result in speciation (formation of new species).

2. Natural Selection - Favours heritable variations that improve survival and reproductive success in a population.

3. Causes of Variation - Mutation, recombination, gene flow, and genetic drift alter gene/allele frequencies in future generations.

4. Types of Natural Selection - Three types:

  • Stabilising - Favours mean/average individuals (peak gets higher & narrower).
  • Directional - Favours one extreme value (peak shifts one side).
  • Disruptive - Favours both extremes (two peaks form).

5. Outcome of Selection - Natural selection causes populations to appear different over time due to the enhanced reproductive success of selected individuals.

CBSE: Class 12

Evolution by Natural Selection vs. Anthropogenic Action

Aspect Natural Selection Anthropogenic Action
Example Moth colour changes pre- and post-industrialisation Development of resistant varieties due to excessive use of herbicides, pesticides and drugs
Time Scale Hundreds to millions of years Months to years
Driving Force Environmental changes and natural predators Human activities and interventions
Outcome Adaptation and survival of better-fit organisms Rapid appearance of resistant organisms/cells
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