Survival of the fittest does not mean survival of the most aggressive.  That is clear to biologists, but apparently is not so clear to many politicians and political philosophers.

What the theory of evolution says is that those members of a species that have the most offspring will pass on their genes to those offspring.  Those who die before they reproduce will not pass on their genes to their offspring.  That is pretty obvious isn't it?

Fitness does not mean aggression or selfishness.  It means fitness.  Cooperation, sharing and love can often be more important to survival.

Dogs are an interesting example.  They survive and thrive and pass on their genes because they are more placid and less aggressive than wolves.  People choose to take care of dogs and their puppies, but choose to hunt and kill wolves because they are afraid of them.  In the case of dogs, fitness to survive involves being lovable to humans, not being aggressive.

Lets look at humans, and our ape ancestors.  Humans, and apes, live in cooperative groups, packs, tribes, communities.  Being a member of a group is necessary to survival.  In tribal societies, exile was one of the very worst punishments.  A human  alone in the wilderness has a very low chance of survival.  Survival for a paleolithic human meant survival of his tribe.  The bonds of friendship, sharing and love within the tribe created the social cohesion needed for survival.  On the other hand, when attacked by wild animals, aggression was necessary to survival.

Depending on the situation, survival of the fittest could mean survival of the groups with the most loving and cooperative members, or survival of the groups with the members most willing to be very aggressive with wild animals attempting to eat their children.