It would be primary since the writer himself is getting the information from a direct source.
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
Answer:
Yes it is helpful
Explanation:
Not only do we live in harmony with these beneficial bacteria, but they are actually essential to our survival. Good bacteria help our bodies digest food and absorb nutrients, and they produce several vitamins in the intestinal tract — including folic acid, niacin, and vitamins B6 and B12.
