Key Concepts

Species inherit their body structures from their ancestor populations

Body structures that are shared between two species are evidence that these two species inherited the shared structure from a common ancestor population

In populations separated into different environments, natural selection causes different changes to happen to each population 

• Causes descendant species to end up with differences in their shared structure

When the environment is mostly the same over time, body structures stay stable

When the environment changes over time, body structures MAY change due to natural selection

Over many generations and very long period of time, many small changes can lead up to large differences in body structures

Among any three species, the two species that are separated MOST recently are the MOST closely related to each other

When two species share a structure that ISN’T shared with a third species, this can be evidence that the first 2 species are MORE closely related to each other than to the third species