Good examples of two species that
appear very different on the surface, but are very homologous in regards to
certain traits are humans and dolphins. The dolphin has a forelimb that is
known as a flipper, this flipper contains a bone structure that is very similar
to that of a human forelimb, an arm. Both species possess a five digits
forelimb. Of course you know that you have five (phalanges) fingers, but a
dolphin also has five finger like phalanges inside of its flipper. This
similarity is derived from a common ancestor millions of years ago. Through the
evolutionary process our five phalange structure has allowed us to very good at
grasping and handling objects, while the five phalange structure of a dolphin’s
flipper is nearly perfectly adapted to assist with movement in the water. To
find a common ancestor for humans and dolphins you would have to go back to
around the time that the dimetrodon roamed the earth. The dimetrodon also possessed
a five phalanges structure in its forelimbs.
Homologous species have very similar traits, while analogous species have very different traits. Great examples of analogous traits are those of a dolphin and a shark. While one may assume that dolphins and sharks are very similar due to both being aquatic species, they are worlds apart genetically. From the outside a shark’s forelimb (pectoral fin) and dolphin’s flipper appear to be very similar, but under the surface the shark does not possess the five phalange structure of the dolphin’s flipper. The pectoral fin of the shark does not have any phalanges inside of it. The pectoral fin of the shark is comprised not of bone like the dolphin, a mammal. The shark is a fish, which has a forelimb comprised of cartilage that bears little resemblance to the dolphin’s flipper. As of yet we have not found a common ancestor between sharks and dolphins. We can assume that dolphins diverged from sharks long before the first mammals roamed the earth so it is not known if any common ancestor possessed this analogous trait.
I'm surprised that not that many people know that even though sharks and dolphins look very similar, they have different bone structures. A shark is not a mammal, therefore it cannot have the phalanges that a dolphin does. But that's just me knowing this because my 7th grade teacher drilled me on the differences between dolphins and sharks. Great blog post by the way!
ReplyDeleteVery Nice! I loved your comparisons. And the picture made me laugh, awesome blog post!
ReplyDeleteFor the most part, good work on your homologous traits. On the issue of ancestry, since both of these organisms are mammals, why do you need to go back to a reptile for the common ancestor? Could you look at early mammals instead?
ReplyDeleteI would actually like to challenge your argument that analogous traits are very different. The problem with analogous traits is that often they appear to be very similar, which leads many people to believe the organisms must be closely related. Where the important difference lies is in their evolutionary history. Yes, they are usually structurally different, but using these relatively superficial evidence for analogies or homologies can lead you astray.
Otherwise good description on the dolphin/shark comparison for their analogous fins.
I think we know quite a bit of ancestry that can confirm these are analogous traits. The shark is a fish and we can expect that the shark inherited its fin structure from it's ancestors (sharks haven't changed much in millions of years). The dolphin, on the other hand, we know arose from land mammals who did not possess fins. This is all we need to know to deduce that the fin structure arose independently and are analogs.
Otherwise, good post.
All around you had great blog. I liked your comparisons between both the homologous and analogous traits for the species you chose.
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