4The wing of a dragonfly and the wing of a butterfly are homologous — they were both inherited from an ancient flying insect
5Not all homologies are obvious if they have been adapted for different roles. For example, the chomping front teeth of a beaver look quite different than the tusks of an elephant. Each is a modification of the basic incisor tooth structure
6Homologies are inherited from common ancestors Homologies are inherited from common ancestors. The octopus limb could only be homologous to the lizard limb if they both inherited the limb from a common ancestor....But they didn’t......so just because an octopus and a lizard have a limb that helps them move does not mean they are homologous.
7Homologies show that Divergent Evolution takes place Divergent Evolution: A common ancestor evolves into new species, which continue to evolve and become less and less alike over time due to differences in the demands driven by the environment.
9Brown Bears and Polar Bears illustrate divergent evolution. Scientists think that a long time ago a group of Brown Bears became geographically separated from the rest. This isolated group acquired new characteristics, such as the ability to eat meat, blubber to keep warm in snowy weather, and a white coat for camouflage. They slowly evolved into Polar Bears
10Adaptive Radiation is an example of Divergent evolution on a shorter, smaller time scale Consider Darwin’s finches...each evolved a new beak to fill a wide range of ecological niches...or ADAPT.
13HINT......there must be a recent common ancestor involved if we are to claim that divergent evolution is taking place, or that two features are homologous.
14So what about ANALOGY?? Consider the following example....
15Both are extinct animals and both of them have saberteeth Both are extinct animals and both of them have saberteeth...but are they homologous?? (Consider that Australia had separated from the Supercontinent a loooooong time ago)Smilodon, the saber-toothed cat, which is a placental mammalThylacosmilus, a marsupial mammal
17They are Analogous!analogy similarity due to convergent evolution not common ancestry CONVERGENT Evolution: When two separate groups of animals evolve to have similar structures
18How do analogies evolve How do analogies evolve? Often, two species face a similar problem or challenge. Evolution may then shape both of them in similar ways — resulting in analogous structures.....like the saber teeth.
19As they weren't inherited from a common ancestor, the saberteeth in Smilodon and Thylacosmilus evolved independently from one another. That means that one lineage on one part of the tree of life evolved saberteeth from normal length teeth, and a different lineage somewhere else on the tree also evolved saberteeth from normal length teeth.
20Another good example of Analogous structures......
21While sugar gliders (marsupials) superficially resemble the placental flying squirrels of North America, the ability to glide through the air evolved independently in these unrelated mammals.
23GAME TIME! Apply your knowledge..... Homology or Analogy??
24Dolphins and Sharks...... both have a streamlined body shape with a triangular fin on the back skeleton made of cartilageskeleton made of boneuse gills to get oxygen from the water in which they swimgo to the surface and breathe atmospheric air in through their blowholesdon't nurse their youngdo nurse their youngdon't have hairdo have hair — they are born with hair around their "noses"
25They are ANALAGOUS....Sharks are closely related to rays, and dolphins are closely related to other mammals. Streamlined bodies and fins are traits that dolphins and sharks evolved separately, both as adaptations for swimming.