D4.1.1 Natural selection as the mechanism driving evolutionary change Notes

Natural Selection Drives Evolutionary Change

1. Over time, this leads to changes in the population, driving evolution.

Key Principles of Natural Selection

1. Overproduction of Offspring:
   1. Most species produce more offspring than the environment can support.
   2. This leads to competition for resources like food, water, and shelter.
2. Variation Among Individuals:
   1. Within a population, individuals vary in traits such as size, color, or speed.
   2. This variation is often due to genetic differences.
3. Struggle for Survival:
   1. Not all individuals survive to reproduce.
   2. Those with traits that give them an advantage (e.g., camouflage or faster speed) are more likely to survive.
4. Differential Reproduction:
   1. Individuals with advantageous traits are more likely to reproduce and pass these traits to the next generation.
5. Change in Population Over Time:
   1. Over many generations, the population evolves as advantageous traits become more common.

Example

Green Sea Turtles

• Female turtles lay hundreds of eggs, but only a few hatchlings survive predators and environmental challenges.
• Those with traits like stronger shells or better swimming abilities are more likely to reach adulthood and reproduce.

How Natural Selection Shapes Populations

1. Adaptation to the Environment:
   1. The traits that increase an organism's fitness are determined by environmental pressures.
   2. As the environment changes, the population evolves to match these new conditions.
2. Gradual vs. Rapid Evolution
   1. While evolution often occurs gradually, it can also happen rapidly in response to sudden environmental changes, such as habitat destruction or climate shifts.

Natural Selection Drives Biodiversity by Shaping Traits for Survival and Reproduction

1. The immense biodiversity seen today is the result of billions of years of natural selection acting on countless populations.
2. By favoring traits that improve survival and reproduction, natural selection has shaped the vast array of life forms and adaptations we observe.

Natural Selection Replacing Lamarckism Is A Paradigm Shift

1. Before Darwin, Lamarckism proposed that organisms could pass on traits acquired during their lifetime.
2. For example, giraffes were thought to have long necks because their ancestors stretched to reach high leaves.

Darwin's Contribution

1. Darwin's theory of natural selection provided a scientific explanation for evolution:
   1. Traits are inherited through genes, not acquired during an organism's lifetime.
   2. Populations evolve over generations, not individuals during their lifetime.