Morphological Homology Molecular homology Fine anatomy Gross anatomy
Homology vs. Analogy Divergent vs. Convergent Evolution & how they relate to.
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Transcript of Homology vs. Analogy Divergent vs. Convergent Evolution & how they relate to.
Homology vs. Analogy
Divergent vs. Convergent Evolution
& how they relate to
HOMOLOGOUS Structures
• homologytraits inherited by two different organisms from a common ancestor
Example of Homology: the tetrapod limb
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 didn’t......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 Darwin’s 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 mammal
Smilodon, the saber-toothed cat, which is a placental mammal
•analogysimilarity due to convergent evolution not common ancestry
CONVERGENT Evolution: When two separate groups of animals evolve to have similar structures
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.
So there you have it.....
HOMOLOGY vs. ANALOGY
GAME TIME!Apply your knowledge.....
Homology or Analogy??
skeleton made of cartilage skeleton 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 young do 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.
The leaves of an oak (left) and the leaves of a gingko (right)
they were both inherited from a common ancestor with leaves.
They are homologous
Now it's your turn to study and prepare for your test on TUESDAY!!