WHAT IF ...
FISH COULD WALK? BIRDS COULD SWIM? HUMANS COULD FLY?
While this may be funny to imagine, these three
organisms actually have features in common. These
are known as:
HOMOLOGOUS
STRUCTURES
The prefix "homo-" means "same," so homology is
the study of similarities between organisms that
have a common ancestor.
WHAT ARE HOMOLOGOUS STRUCTURES?
Homologous structures are similar characteristics
between related species that have different functions.
In other words, they have the same ancestor but
different functions. The picture below shows that
humans, dogs, birds, and whales have
similar/homologous structures.
HUMAN DOG BIRD
WHALE
PHOTO CREDIT: WIKIMEDIA COMMONS
This concept is similar
to how identical twins
are from the same
parents and can look
really similar but still
have different interests!
LET'S LOOK AT AN EXAMPLE OF THIS CONCEPT ...
BIRD
EARLY LOBEFINNED FISH
EARLY
AMPHIBIAN
EARLY REPTILE
HUMAN
PHOTO CREDIT: UMMNH, EVOLUTION: LIFE THROUGH TIME EXHIBIT - 2ND FLOOR OF UMMNH
This graphic shows how
human arm bones and
bird wing bones evolved
from Eusthenonteron,
which is a lobe-finned
fish. This means that
Eusthenonteron is their
common ancestor.
ACTIVITY
FILL IN THE BLANK ...
While the bones in the fish, bird,
and human are the same, they have
_________ functions. This makes the
bones _____________ structures.
Look at the bottom of this
infographic for answers!
Using homologous structures, we can work backwards to
find out which species are related and where they shared
common ancestors based on the similarities and differences
they hold!