Fossil evidence, and biographical evidence.
In natural selection, there are three main things you need to know. There must be a variance in the genepool of course, or else to selection or evolution will take place. There also must be a selective force and time. Now, lets say that there is a population of many colored moths. But lets say that the brown colored moth blends in with the environment. This means that predators (selective force in this case) will have a much harder time finding these brown moths instead of easily finding some of the other colored moths (variation). This means that the brown moths will survive at a much higher rate because the are harder to find, and over time, the gene pool will narrow down to just brown moths because the rest of the moths die out due to predators and competition. This also means that this moth species has evolved over time to just become the brown colored moths only. Hope you can understand this but feel free to ask for clarification.
Unicellular organisms are living things made up of only one cell. For example, bacteria and yeast are unicellular. Multicellular organism are made up of more than one cell. Some examples of a multicellular organisms are humans and animals.
Answer:
Only the strongest would survive each year and be able to breed
Explanation:
According to Darwin's theory of evolution if an animal were to be put into terrain whether local or new, the animal would need to adapt as its surrounding slowly change. If said animal is unable to adapt in time it will perish or be unable to produce strong offspring that will survive.