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AP Bio



Unit 7

7.1 Introduction to Natural Selection

2 min readmay 31, 2020


Lani Himegarner

Survival of the Fittest

Natural selection is one of the main components of evolution. It can actually change the phenotypic ratios of species and/or populations using “survival of the fittest”. In other words, those that have traits that are more advantageous to their survival are more likely to survive and pass those traits onto their offspring.

Theory of Evolution

This thought was first introduced by Charles Darwin in his Theory of Evolution. After studying birds in South America, he proposed this theory based on three major propositions:
  1. Species change over time
  2. Divergent species share a common ancestor
  3. Natural Selection is the mechanism that produces these changes in species/populations
He saw this first hand when he realized that the finch (bird) species had adapted to food that they could access. Some had bigger beaks for cracking bigger nuts, while others had smaller beaks to reach the smaller nuts in smaller places. These species may have actually originated with the same species, but diverged with two different identifying traits that ultimately played an integral role in their survival.

Image courtesy of Giphy.


Evolutionary fitness refers to the phenotypes that are directly related to the survival of a species or population. If a trait is known for its “fitness”, it just means that it aids in the survival of that particular species or population. Some examples of this would be coloring that can aid with camouflage.  The individuals without an advantageous phenotype would be spotted by predators much faster than those that blend in with their surroundings, and would therefore die before they can reproduce and pass their disadvantageous traits onto offspring. Therefore, that phenotype could eventually die out altogether, leaving only those with evolutionary fitness left to survive and reproduce.
In fact, the surrounding environment plays into natural selection as well. In any biome, the population will be affected by both biotic (living) and abiotic (nonliving) factors. Examples of biotic factors would be vegetation, predators and prey, etc. Abiotic factors would include things like soil, temperature, and other non-living environmental components.
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