The wing of a dragonfly and the wing of a butterfly are homologous they were both inherited from an ancient flying insect
Not 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
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 didnt......so just because an octopus and a lizard have a limb that helps them move does not mean they are homologous.
Homologies 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.
Brown 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
Adaptive Radiation is an example of Divergent evolution on a shorter, smaller time scale Consider Darwins finches...each evolved a new beak to fill a wide range of ecological niches...or ADAPT.
HINT......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.
So what about ANALOGY?? Consider the following example....
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) Thylacosmilus, a marsupial mammalmarsupial mammal Smilodon, the saber-toothed cat, which is a placental mammalplacental mammal
analogy similarity due to convergent evolution not common ancestry CONVERGENT Evolution: When two separate groups of animals evolve to have similar structuresconvergent evolution They are Analogous !
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.
As 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.
Another good example of Analogous structures......
While 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.
GAME TIME! Apply your knowledge..... Homology or Analogy??
skeleton made of cartilageskeleton made of bone use gills to get oxygen from the water in which they swim go to the surface and breathe atmospheric air in through their blowholes don't nurse their youngdo nurse their young don't have hair do have hair they are born with hair around their "noses" Dolphins and Sharks...... both have a streamlined body shape with a triangular fin on the back
They 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.