Here's why:
* Evolution is the change in the genetic makeup of a population over time. This change happens through processes like natural selection, genetic drift, and gene flow.
* Individuals do not change their genetic makeup during their lifetime. While an individual might develop adaptations within their lifetime (like gaining muscle mass from exercise), these changes are not passed down to their offspring.
* Evolutionary changes occur through the inheritance of genetic variations. These variations arise from mutations, which are random changes in an organism's DNA.
* Natural selection acts on individuals, but the population evolves. Individuals with traits that are more advantageous in their environment are more likely to survive and reproduce, passing those traits on to their offspring. Over time, this leads to a change in the overall genetic makeup of the population.
Analogy: Think of it like this: if you have a bag of marbles, each marble representing an individual organism, and you want to change the color of the marbles in the bag, you can't just change the color of one marble. You need to replace the marbles with different colored ones, or allow for new marbles with different colors to be introduced into the bag.
Therefore, while individuals can change and adapt to their environment, evolution is a process that affects the entire population over generations, driven by changes in the frequency of alleles (versions of genes) within that population.
