Fitness is determined by

Averaging the fitness of its members.

Explanation:

The fitness of a whole population can also be determined by averaging the fitness of its members. Absolute fitness is the ratio between the number of individuals with a genotype before selection versus after selection. Fitness is usually discussed in terms of genotypes, or collection of genes.

in a chemical reaction, the atoms and molecules produced by the reaction are called products. no new atoms are created, and no atoms are destroyed. in a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.