Darwin’s theory of evolution by natural selection explains how species change over time due to differences in survival and reproduction. The key principles of this theory are:
1. Overproduction:
Organisms produce more offspring than can survive. For example, a frog lays hundreds of eggs, but only a few tadpoles reach adulthood.
2. Variation:
Individuals in a population have variations in their traits. Some traits provide an advantage in survival, while others do not. For instance, in a population of rabbits, some may have thicker fur that helps them survive in cold weather.
3. Struggle for Existence:
Since resources like food, water, and shelter are limited, organisms compete for survival. Those with beneficial traits are more likely to survive and reproduce.
4. Survival of the Fittest:
Individuals with advantageous traits (adaptations) are more likely to survive and reproduce, passing those traits to their offspring. For example, giraffes with longer necks could reach higher branches for food, increasing their survival chances.
5. Inheritance of Beneficial Traits:
Over generations, beneficial traits become more common in the population. This gradual process leads to the evolution of new species.
Example: The Peppered Moth
Before the Industrial Revolution, light-colored moths were more common because they blended with tree bark. When factories released soot into the air, the tree trunks darkened, and dark-colored moths became more common because they were less visible to predators. This is an example of natural selection in action.
Natural selection continues to shape the evolution of species, allowing them to adapt to changing environments.