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Similarities and differences: understanding homology and analogy (High School level) :

Test your understanding

In this module, you learned that homologies are traits that different lineages inherited from their common ancestor. Homologies are evidence that different species shared a common ancestor. Analogies, on the other hand, are similar traits that were not inherited from a common ancestor but that evolved separately. Analogies often exist because two different lineages became adapted for similar lifestyles.

Sugar gliders and flying squirrels look amazingly similar. They are both furry animals of about the same size, with big eyes and a white belly. And they both glide from treetops using a thin piece of skin that is stretched between their legs. This piece of skin helps keep them stable while gliding.
Flying squirrel in mid-glide Sugar glider in mid-glide
Flying squirrel Sugar glider

However, these animals also have some key differences:

  • Sugar gliders live in Australia, and flying squirrels live in North America.

  • Sugar gliders have a pouch (like a kangaroo does), which provides shelter and safety for their tiny babies — at birth, a baby sugar glider is smaller than a peanut! Flying squirrels, on the other hand, have much larger babies and no pouch.
By studying their genes and other traits, biologists have figured out that sugar gliders and flying squirrels are probably not very closely related. Sugar gliders are marsupial mammals and flying squirrels are placental mammals.

Sugar gliders are marsupials, and flying squirrels are placentals.

Considering all of the evidence, are the "wings" (actually flaps of skin stretched between the legs) of sugar gliders and flying squirrels homologous or analogous structures?

Flying squirrel photo courtesy of Mona Rutger, backtothewild.com; Sugar glider photo courtesy of The Mouses House, Queensland, Australia.

Homology & Analogy
page 12 of 12

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See more examples of homology and examples of analogy.