Evidence of evolution. Scientists support the evidence of evolution because of the adaptations organisms used to have in the past compared to the present. For example, humans have organs in their bodies they don't need, but must have been used in ancient times. They can also find that humans have a common ancestor such as monkeys because of the DNA similarities and many adaptations. Hopefully this answered most of your question.
All of those are similar to each other because they are all weeds, or in other words they are all different types of grasses.
It is called a population since they are all the same species
