Analogy: Squirrels and Sugar Gliders
Beyond being cute and cuddly, flying squirrels and sugar gliders have many striking similarities: big eyes, a white belly, and a thin piece of skin stretched between their arms and legs, a trait which helps them "glide" and remain stable when leaping from high places.
But sugar gliders and flying squirrels also have some key differences. Most importantly, they reproduce and bear their babies in fundamentally different ways:
Flying squirrels and sugar gliders are only distantly related. So why do they look so similar then? Their gliding "wings" and big eyes are analogous structures. Natural selection independently adapted both lineages for similar lifestyles: leaping from treetops (hence, the gliding "wings") and foraging at night (hence, the big eyes).
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Flying squirrel photo courtesy of Mona Rutger, backtothewild.com; Sugar glider photo courtesy of The Mouses House, Queensland, Australia.
Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California