Evolution and Natural Selection: Understanding the Adaptation of Living Organisms
Problem — How do species evolve over time and adapt to their environment?
How do species evolve over time and adapt to their environment?
- Understand what biological evolution is.
- Identify the role of natural selection in evolution.
- Know how genetic variations influence survival and reproduction of individuals.
- Understand that evolution happens at the population level, over many generations.
Part 1: What is Biological Evolution?
Evolution is the process by which populations of a species change over generations.
These changes can affect shape, behavior, or other characteristics.
Evolution corresponds to a transformation of populations through time: certain traits (linked to genes) become more or less common depending on environmental conditions.
We don't say a species "evolves to" adapt: evolution has no intention. Individuals have differences, and over generations, some traits may be favored.
- Evolution occurs over many generations and involves populations.
- It corresponds to changes in the frequency of certain traits (linked to genes).
Part 2: Natural Selection
Natural selection is a mechanism that favors, in a given environment, individuals with traits that give them an advantage.
They then have a greater chance to survive and especially to reproduce: we say they have better reproductive success.
If these traits are hereditary, they are more often passed on to the next generations.
| Principle | According to the course |
|---|---|
| Variation | Individuals of the same species are not all identical |
| Selection | In an environment, some traits give an advantage |
| Reproductive Success | Favored individuals leave more offspring |
| Transmission | Advantageous hereditary traits become more frequent |
In a cold environment, individuals with thicker fur can better resist, survive longer, and leave more offspring. Over generations, thick fur becomes more common in the population.
- Natural selection favors individuals with better reproductive success in a given environment.
- Advantageous hereditary traits become more frequent over generations.
Part 3: Genetic Variations and Their Importance
Individuals of the same species exhibit genetic variations (differences in certain genes).
These variations cause differences in traits.
Without variation, natural selection could not act.
- Mutations: random changes in DNA that can create new versions of a gene.
- Genetic recombination: reshuffling of genes during the formation of reproductive cells and fertilization.
| Key idea | According to the course |
|---|---|
| Genetic Variations | Present in individuals of the same species |
| Origin of differences | Variations explain different traits |
| Condition for selection | No variation, no natural selection |
In a population of bacteria, some are naturally more resistant to an antibiotic (variation). The antibiotic mainly kills non-resistant bacteria. Resistant bacteria survive and multiply: over generations, the population becomes mostly resistant.
- Genetic variations (mutations + recombination) make individuals different.
- Natural selection can then favor certain traits, which causes the population to evolve.
Evolution corresponds to changes in populations over generations. It is made possible by genetic variations (mutations and recombination). Natural selection favors, in a given environment, individuals whose certain hereditary traits increase survival and especially reproduction: these traits then become more frequent. This mechanism explains adaptation and the diversity of life.