Answer:
organisms that are best adapted to the environment they are placed in will survive long enough to pass on their genes to their offspring while other organisms will become extinct.
Explanation:
Every now and then an organism in a species will undergo a mutation in their DNA. This mutation could do nothing but it may also lead them to getting, for example, longer legs than their counterparts. This may help them survive longer than other organisms as this mutated adaptation may help them run faster away from predators. These organisms will probably be able to outlive their less fortunate counterparts and they can then pass on their genes to their offspring, who will then gain the same mutated genes which will help them live longer. This continues for generations with the organisms who don't have the more specialised adaptation dying out as they are not able to escape from their predators
Medicine. Most of the things we consider medicine are only helpful if we're already in bad condition, taking medicine while being completely fine can have terrible side effects on your body.
Democracy, it keeps away a tyrannical overlord from controlling the control, but sometimes it's impossible for different sections of government to agree on certain things, and this prolongs the process sometimes making democracy seem a little unreliable compared to the fast paced solidified decision of a single ruler.
Eating. Doing anything in excess can be harmful, but especially eating in the case of most Americans. Even with the health reforms of today, and dietary programs, many Americans are obese and suffer from type 2 diabetes simply from over-eating.
Those are just three examples I could think of.
