a.
Human “Tailbone” and the chimpanzee ancestor
tail
b.
The tailbone in humans has its name because it
comes from the same homologous structure that gives other species its tail. In
humans it is called “vestigial” because it is the last “vestige” or trait of
what was once a tail in a common ancestor. In humans, the tailbone is no longer
useful because we do not grow or need tails anymore, but we have a common
ancestor with the chimpanzee who did need a tail. Mammals who have tails use
them for balance, but as humans diverged genetically from our common chimpanzee
ancestor millions of years ago, we learned to walk on two legs without using a
tail for balance.
c.
Chimpanzees are the closest living ancestor of
humans, but even the chimpanzee split from our common ancestor around 13
million years ago. Humans and chimpanzees share a common ancestor which is described
as ape-like. When humans made the genetic divergence 13 million years ago, the
tail was no longer needed and thus began to disappear.
d.
2.
a.
I chose the penguin and the fish fins for the analogous
trait. Both species have fins on their bodies used to navigate through the
water.
b.
Both species have fins which are used to
navigate through the water. However, the fish fin is more specifically
developed for water since it spends its entire life in the water. The penguin
fin is more webbed because it need to balance as it walks on land as well as
using it to propel it through the water. Fish also have a few different kinds
of fins on their bodies for different purposes all related to swimming through
the water.
c.
There are no common ancestors between the fish
and the penguin. The fish is a sea animal and has sea animal ancestors, while
the penguin has more primarily land ancestors.
d. 
You made an excellent point about humans losing their tailbones. I completely agree about the tailbones not needed anymore in humans. There are a few species of apes that are tailless too such as orangutans, gorillas, and chimpanzees.
ReplyDeleteI agree that the flippers of penguins and the fins fish are analogous. The fins of fish are composed of bony or soft spines. The bone structure of the flippers for the penguins are similar to that of bird wings. I agree that both are used for swimming.
Part A asks for a description, not just identification.
ReplyDeleteUnfortunately, chimpanzees, like apes, do not have a tail. Not sure if this image will come through but here is the link:
http://www.dickroman.com/Portfolio/Tails/i-J6B76VH
Completely tailless, just like humans. A better comparison would have been humans and New World monkeys (like a spider monkey) or even with Old World monkeys, such as baboons, who do have a stub of a tail, though it isn't all that useful except as a muscle attachment. And human tailbones do have that same function. It serves as a muscle attachment for important perineal muscle on the pelvic floor. They aren't completely useless.
Yes, chimpanzees and humans are closely related genetically but that doesn't guarantee the the trait in question is from common ancestry. We do have some genetic differences! So you also need to check out the anatomy to confirm that these are homologs. In this case, it would have helped you discover that both humans and chimps are tailless.
Images are fine, but again an image of the posterior of the chimp would have be helpful.
Better description in Part A for your analogous traits and good discussion on the traits themselves.
As explained in the guidelines, all organisms have a common ancestor if you go back far enough in their evolutionary history. In this case, the common ancestor of penguins and fish was an early fish, which gave rise to not only modern fish but also amphibians, then reptiles, then mammals and birds. So the modern fish did inherit its fin structure from that common ancestor. Does that make these fins homologs? Well, it depends upon how the penguin got its fins. Penguin fins are derived bird wings and we know quite a bit about bird evolution, namely that wings evolved during the split from reptiles. That means that wings (and the penguin fins) arose independently from that common fish ancestor and confirms that these are indeed analogs.
Good images.
I think this post is giving good examples and actually is helping me understand better in how species have a specific trait. I am keeping in mind that these traits did not work out, as explained in the previous comment. However it has still been informative especially reading your post as well as the professors comments. Seeing post with different examples is helpful to me, I also loved the picture of the baby and the baby chimp.
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