1. Sources of Genetic Variation:
* Mutations: Random changes in DNA sequence. These are the ultimate source of new genetic material.
* Recombination: During sexual reproduction, chromosomes exchange genetic material, shuffling existing alleles.
* Gene flow: The movement of genes between populations.
2. Natural Selection:
* Environmental Pressures: The environment presents challenges (e.g., climate change, food scarcity, predators).
* Survival and Reproduction: Individuals with traits better suited to the environment are more likely to survive and reproduce, passing on their genes.
* Differential Reproduction: Individuals with less advantageous traits are less likely to survive and reproduce, leading to a decrease in those traits over generations.
3. Speciation:
* Isolation: Populations become geographically or reproductively isolated. This prevents gene flow between them.
* Genetic Divergence: Over time, isolated populations accumulate different mutations and experience different selection pressures, leading to genetic divergence.
* Reproductive Isolation: Eventually, the populations may evolve to the point where they can no longer interbreed. This marks the formation of distinct species.
Here's an example:
Imagine a population of beetles living on a mountainside. Some beetles have a gene that allows them to better digest a type of plant growing on the higher slopes. Over time, these beetles are more likely to survive and reproduce, passing on the gene to their offspring.
Now imagine a landslide that isolates the beetles on the lower slopes. These beetles don't have the same food source and face different challenges. Over time, the lower slope beetles may evolve different traits that make them better adapted to their environment.
Eventually, the two groups of beetles may become so genetically distinct that they can no longer interbreed. This is speciation.
Key Points:
* Genetic variation is random, but natural selection is not.
* Speciation is a gradual process that can take many generations.
* The environment plays a critical role in driving evolution and speciation.
* Speciation is a continuous process, and new species are constantly emerging.
