Humans and bats share homologous traits. The front limbs of both humans and bats have the same general structure. Both species's limbs (specifically arms in the case of humans) end in five digits. These structures do not look similar to the human eye. A bat has four phalanges and a thumb or "claw." The thumb is the only digit that has an ranged of motion separate from the rest. In comparison, human hands have full range of motion— making a fist, holding/grabbing items, moving fingers individually. Humans and bats use their front limbs for different actions, explaining why the structures look different.
Originally, the common ancestor was that of a mammal, more specifically a vertebrate. This homologous trait would have had to be passed down from ancestors who had skeletons.
Sharks and dolphins share the trait of having fins. This trait is analogous. Both species use their find for movement in the water. Although these traits look similar, a shark's fin is mainly cartilage while a dolphin's fin does not have internal support within the structure. Both fins allow for the shark or dolphin to swim— movement is the main purpose. Sharks came from a lineage of fish while dolphins are mammals.
Sharks were swimming in the water while dolphins were still, at a time before they evolved, inhabiting land. It is possibly they a common ancestor could have possessed this trait, but it is not genetically related. Fins on dolphins are a sign of evolution.
The homologous connection you have pointed out between humans and bats was very interesting; the connection between the similar structure of the bat’s wings and a humans hand. With the human hand being able to accomplish more movement, range of motion and moveable thumbs whereas for the Bat is limited to its abilities.
ReplyDeleteThe analogous traits between a shark and dolphin’s fins interesting. I did not know that a shark’s fin consisted mostly of cartilage whereas a dolphin’s fin did not have much structural support.
Missing the opening description of your homologous species?
ReplyDelete"Humans and bats use their front limbs for different actions..."
Yes... but what are those different actions? :-) Let's fully explain your argument here.
"Originally, the common ancestor was that of a mammal, more specifically a vertebrate."
Actually, since all mammals are vertebrates but not all vertebrates are mammals, identifying a common mammalian ancestor IS more specific. And because we know from fossil evidence that archaic mammals possessed the primitive mammalian limb structure and passed it onto these extant species, that is the information we need to know to confirm homologous status.
Again, missing opening description of analogous species.
Good description of the analogous traits.
"It is possibly they a common ancestor could have possessed this trait, but it is not genetically related."
Two problems with this. First, ALL organisms share a common ancestor if you go back far enough. Second, a common ancestor, by definition, would be genetically related.
Sharks and dolphins do share a distant common ancestor, and that ancestor DID have the fin structure you are comparing as that ancestor was an archaic fish. This means that the shark actually did inherit these structures from the common ancestor. But as you do point out, dolphins arose from land mammals and their fin structure arose after that split from terrestrial ancestors. This means this trait arose independently in dolphins, even if it didn't for the shark.
Good images.