Rucete ✏ Biology In a Nutshell
1. Darwin’s Theory of Natural Selection
- Populations possess enormous reproductive potential.
- Population size remains relatively stable over time.
- Resources are limited, leading to competition.
- Individuals compete for survival and reproduction.
- There is variation among individuals in a population.
- Much of this variation is heritable (passed on to offspring).
- Only the most fit individuals survive and reproduce.
- Favorable traits accumulate, leading to evolution over generations.
2. Types of Selection
a) Stabilizing Selection
- Selects against extreme traits, favoring average phenotypes.
- Reduces variation in the population.
- Example: human birth weight (very low or high weight has higher mortality).
b) Directional Selection
- Favors one extreme of a trait.
- Leads to a shift in allele frequency over time.
- Example: evolution of insecticide resistance, or dark-colored peppered moths during the Industrial Revolution.
c) Disruptive (Diversifying) Selection
- Favors both extremes of a trait over the average.
- Can lead to speciation if the population splits.
- Example: birds with either very small or very large beaks favored over medium beaks.
d) Sexual Selection
- Occurs when traits increase mating success, even if they don’t increase survival.
- Often results in sexual dimorphism (males and females look different).
- Example: bright plumage in male peacocks.
e) Artificial Selection
- Human-directed breeding for desired traits.
- Example: selective breeding of dogs, crops, or livestock.
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Biology in a nutshell