7.1 Introduction to Natural Selection
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Natural Selection | 自然选择 | A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals. |
| Evolutionary Fitness | 进化适应度 | The measurable contribution an individual makes to the gene pool of the next generation (i.e., reproductive success). |
| Phenotype | 表型 | The observable physical or biochemical characteristics of an organism, as determined by genetic makeup and environmental influences. |
| Differential Survival | 差异生存 | The concept that some individuals survive longer and better than others due to favorable traits in a specific environment. |
1. Darwin's Mechanism of Evolution
Charles Darwin did not invent the concept of evolution; rather, he proposed the major scientific mechanism for how it occurs: Natural Selection.
According to Darwin's theory, the natural world is characterized by constant struggle. The process of natural selection relies on several key observations and inferences:
- Overpopulation: Species have the potential to produce far more offspring than the environment can support.
- Competition: Because resources (food, space, mates) are limited, this overproduction leads to fierce competition for survival.
- Variation: Individuals in a population exhibit variations in their heritable traits (phenotypes).
- Differential Survival and Reproduction: Individuals with more favorable phenotypes (adaptations that suit their environment) are more likely to survive the competition and produce more offspring.
- Descent with Modification: Because these favorable traits are heritable, they are passed to subsequent generations. Over time, the population's characteristics change.
2. Redefining "Fitness"
In everyday language, "fitness" usually means physical strength, speed, or health. In AP Biology, however, Evolutionary Fitness has a very strict and specific definition.
Core Concept: Evolutionary Fitness
Evolutionary fitness is measured strictly by reproductive success.
It doesn't matter if an animal is the fastest, the strongest, or lives the longest. If it is completely sterile and leaves zero offspring, its evolutionary fitness is zero. The "fittest" individuals are simply those who leave the most viable, fertile offspring in the next generation.