1. Creating Selective Pressures:
* Resource Availability: Limited food, water, or shelter creates competition among individuals. Those with traits that allow them to acquire these resources more effectively have a higher chance of survival and reproduction.
* Climate: Changes in temperature, precipitation, or other climatic conditions can favor individuals with adaptations suited to the new environment. For example, thicker fur in colder climates.
* Predators: The presence of predators creates a strong selective pressure, favoring individuals with traits that improve their ability to escape (speed, camouflage, vigilance) or defend themselves.
* Disease: Disease outbreaks can eliminate individuals susceptible to infection, favoring those with resistance.
2. Shaping Variation:
* Mutations: Environmental factors can increase the rate of mutations, introducing new genetic variations into a population.
* Gene Flow: Migration of individuals from different environments can introduce new alleles into a population, increasing genetic diversity.
3. Driving Selection:
* Differential Reproduction: Individuals with advantageous traits are more likely to survive, reproduce, and pass those traits to their offspring.
* Survival of the Fittest: This phrase, though often misinterpreted, highlights the idea that individuals with traits that best suit the environment are more likely to survive and reproduce, passing on those advantageous traits to their offspring.
Example:
Consider the evolution of the peppered moth. Before the Industrial Revolution, the moth's light coloration provided camouflage against lichen-covered trees. However, pollution from factories darkened the tree bark. Darker moths had a survival advantage, as they blended in better and were less likely to be eaten by birds. Over time, the frequency of the dark moth allele increased in the population. This shift in allele frequencies reflects the influence of environmental changes on natural selection.
Key Takeaways:
* Environmental factors drive natural selection by creating selective pressures that favor individuals with advantageous traits.
* Natural selection leads to the evolution of populations over time, as advantageous traits become more common.
* The environment is constantly changing, which means that the selective pressures acting on populations are also constantly changing.
This continuous interplay between environmental factors and natural selection drives the evolution of life on Earth, leading to the incredible diversity we see today.
