Final answer:
Evolution by natural selection is inevitable due to three main postulates: inherited characteristics, overproduction of offspring leading to competition for limited resources, and variation in offspring's inherited characteristics.
Step-by-step explanation:
The three postulates that make evolution by means of natural selection inevitable are as follows:
- Most characteristics of organisms are inherited, or passed from parent to offspring. This ensured that advantageous traits could be passed to successive generations.
- More offspring are produced than can survive due to limited resources. This overproduction leads to a struggle for existence and competition for resources.
- Variation in characteristics among offspring, and these variations are inherited. Those with advantageous variations are more likely to survive and reproduce, thus passing on their traits.
Darwin and Wallace concluded that these principles lead to natural selection, where organisms with traits better suited to their environment are more likely to survive, reproduce, and thus pass on these advantageous traits. Over time, this leads to populations evolving and adapting to their local environments.