Explain what you think the phrase 'survival of the fittest' means.

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

Organisms more adapted to their environment are more likely to survive than organisms that aren't.

Explanation:

Organisms that are more well equiped to where they live will live longer than an animal who is far less adapted. One example could be if a polar bear and rattle snake live in the desert. The rattle snake is more adapted to the desert than the polar bear, therefore it will also be more likely to survive.