1. Evolution is based on changes in gene frequencies: Evolution is driven by changes in the relative frequency of different alleles (gene variations) within a population. These changes occur due to various mechanisms like natural selection, genetic drift, mutation, and gene flow.
2. Individuals don't change their genes: While individuals may change during their lifetime due to environmental factors, these changes are not heritable. Only changes in the genetic code of an organism can be passed on to offspring.
3. Individuals are not representative of the population: A single organism's characteristics do not represent the genetic makeup of the entire population. Evolutionary changes are reflected in the overall shift in gene frequencies across the population.
4. Natural selection acts on variation within a population: Natural selection favors individuals with advantageous traits that increase their chances of survival and reproduction. This leads to an increase in the frequency of those advantageous alleles within the population over time.
Example:
Imagine a population of beetles with variations in color. Some are green, some are brown. If the environment changes and brown beetles are better camouflaged from predators, they are more likely to survive and reproduce. This leads to an increase in the frequency of the brown allele in the population, making the next generation more likely to have brown beetles.
This process of change in gene frequencies across generations, not within an individual, is the essence of evolution.
