Evidence of Change: Homologous Body Structures
As the comparative anatomist in your group, your job is to present the evidence of the homologous
structures and how it supports evolution. You have been provided with some readings and
diagrams that will help your case, along with some guiding questions that will help the other
scientists understand your field.
Start by looking through the diagrams and articles and in your book (p. 384-385), then answer the
questions that highlight the important points of homologous structures and how it provides
evidence for evolution. Be sure that you are able to explain these main points to your group
members.
1. What is a homologous structure?
Homologous structures are bones with similar structures and similar developments but
different functions. They have different niches, or jobs, due to variations in the population
that accumulated over time and served as adaptations. Homologous structures are the result
of divergent evolution.
2. How are homologous structures used by comparative anatomists to provide evidence of
evolution?
Homologous structures show that species have a common ancestor and over time have
evolved from their ancestor to carry out different functions.
3. Explain how comparative anatomy would explain the relationship between whales and
humans.
Whales and humans have the same bone structure in their arm/fin. Both have a humerus,
radius, ulna, carpals, metacarpals, and phalanges connected in the same way. This bone
structure is similar in both species because both are derived from a common ancestor that
had a similar bone structure.
4. What is a vestigial organ? What is an example of a vestigial organ?
Vestigial organs are traces of homologous organs and currently serve no useful function in
the organism. There are many examples of vestigial organs in nature: wings on flightless
birds, hind leg bones in whales, erector pili and body hair, the human tailbone, the blind fish
Astyanax Mexicanus, wisdom teeth in humans, sexual organs of dandelions, fake sex in
Virgin Whiptail Lizards (vestigial behavior), male breast tissue and nipples, and the human
appendix.
Vestigial organs are still present in species today because they may not affect an organism’s
ability to survive and reproduce. Thus, natural selection would not eliminate from the
population.
5. What is an analogous structure?
Analogous structures are structures that have separate evolutionary origins, but are
superficially similar because they evolved to serve the same function. Analogous structures
are the result of convergent evolution.
6. How would you explain the relationship between birds and bats and bees? (They all have
wings, but…were wings evolved more than once?) Which organisms are more closely
related?
Birds, bats, and bees did not inherit wings from a common ancestor with wings, but birds
and bats did inherit forelimbs from a common ancestor with forelimbs. The wings are
analogous structures, so they cannot be used to determine how closely related the species are
to one another.
7. What evidence is there that connects baleen whales to other toothed whales and mammals?
Hypothesize as to why baleen whales don’t have teeth in their adult stage of life.
Baleen whales possess teeth in the early fetal stage and lose them before birth. The
possession of teeth in fetal baleen whales provides evidence of common ancestry with
toothed whales and other mammals. In addition, ancient baleen whales bore a full set of
teeth.