Analogies and Homologies, ancestral or derived?

Different ways we can determine ancestral or derived characteristics: Example: the tail and the outgroup

1. We can look at the outgroup. Is the Shinagawa tail a primitive or derived characteristic? They are primates. When you go back far enough in history, you see that primates did have tails. One way that you could look at this is by looking at the outgroup. Compare them to fliying lemurs, who are not primates. You could determine through that, that the primitive characteristic in many mammals is a tail.

Analogies, and two examples

Analogous structures that have similar form or function, but that were not present in the last common ancestor of those groups. This is related to convergent evolution, and is in stark contrast to homologies. An example of this could be wings: the fact that all these animals have wings is not a product of the same ancestor, but simply convergent evolution. Think about the structure of the wings in these animals - they are fundamentally different. The bones in bats and the bones in birds are fundamentally different. So this could be something that tells you that it is convergent evolution. Even dolphins and sharks could seem similar, but they are so different. We are more similar to a dolphin than a dolphin is to a shark.

So what do we need to avoid when determining similarities?

Ancestral traits and analogous structures.

Test: What about egg laying?

Chickens and duck-billed platypus both lay eggs, but not us. So are they more closely related? No. This statement is based on ancestral characters which is not very meaningful.

Test: What about birds and us and bipedalism?

Clearly analogous. Birds are bipedal from ancestry of dinosaurs, as opposed to us which is very recent adaption.

What should we look at instead?

Derived characteristics. We have to know which characteristics are primitive and which characteristics are derived. Working out if something is an analogy is not easy. We have a lot of potential characters which is an example of analogy which we could mistake for a homology.

Test: What about fingers in us and lizards?

Fingers on us and lizards - also ancestral. What our ancestors had and what we've derived from them.

Define Convergent Evolution

In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. In other words, convergent evolution means that the two species who have similar characteristics DO NOT come from the same ancestor - these traits are thus derived.

Who came up with these two categories, perhaps even before evolution was a thing?

Richard Owen

Different ways to determine ancestral or derived characteristics: example of a tail and the embryology

You could also look at embryology. During the human embryo, we have tails and then we lose them. This shows a tail as a primitive feature.

Define: Homologies and Homologous structures and an example!

homologous structures or traits, which have a common origin, but not necessarily similar function. This is related to divergent evolution. Now we are looking at the arm of a human and the flipper of a whale. They are completely different structures superficially. Our arms and a whale's flipper has completely different functions. Are the bones the same? No, but they are quite similar - radius, finger bone, humerus