Evolution is often described as "survival of the fittest." how would a biologist best measure fitness from the perspective of evolution?

By the number of offsprings

Explanation:

Fitness is a key concept in evolution and it is embedded at the core of Natural selection.That is 'survival for the fittest'

Evolutionary fitness is measured by the survival and reproduction ability of the organism. This will determine the size of its genetic contribution to the next generation.

Therefore the more an organism survives to reproduce, the more its genes will be represented in the next generation and beyond. This organism will be considered fit.

layer 3 is younger than layer 6.