Key Concepts

Inheritance of Body Structures

Species inherit their body structures from ancestor populations.

Shared Structures as Evidence

Body structures shared between species indicate inheritance from a common ancestor population.

Natural Selection in Different Environments

Populations in varied environments undergo distinct changes due to natural selection.

Differences in Shared Structures

Natural selection leads to differences in shared structures among descendant species.

Stability in Stable Environments

Body structures remain stable when the environment is consistent over time.

Changes in Changing Environments

Body structures may change due to natural selection when the environment changes.

Accumulation of Changes

Small changes over many generations can result in significant differences in body structures.

Closely Related Species

Species separated most recently are the most closely related among any three species.

Evidence of Relatedness

Shared structures not present in a third species suggest closer relatedness between the first two species.