Homologies are not just anatomy
We tend to think of homologies in terms of anatomy: the tetrapod limb,
insect wings, vertebrate eyes. However, anatomical homologies are just
one of many sorts of homologies. Any heritable trait anything that can
be directly or indirectly encoded in DNA can be a homology:
- A simple trait
Among milkweed species, having milky sap is a homology.
- A complex structure
The antennae of beetles and moths are
homologous, for example.
- A gene sequence
The gene that codes for the protein insulin is
homologous in humans and cows; both sequences descended from the same
ancestral gene sequence.
- A behavior
Birds and crocodiles both provide parental care to their
offspring; this behavior was inherited from a common ancestor and is