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My question is contextualised for basic phylogeny knowledge. Here is my understanding: similar or identical traits between any two species, at the basic level, can be either homologous, meaning the trait is developed from a common ancestor, or homoplastic, meaning that the trait was independently developed.

Homologous traits can be either ancestral or derived, and derived traits are a subset of ancestral traits as derived traits need to be from the most recent common ancestor.

Homoplastic traits can be analogous, meaning they developed independently without any common ancestor or commmon initial trait, or can be traits that arose due to convergence, where species with the same (distance/close) ancestor independently developed the traits.

Please evaluate whether my understanding is correct.

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As a complement to the other answer: homoplasy and analogy are not synonyms, but not for the reason described in your question.

According to Ridley (2011):

Analogy: A term mainly not used in this edition of the text, but close in meaning to homoplasy. That is, a character shared by a set of species but not present in their common ancestor — a convergently evolved character. Some biologists distinguish between homoplasies and analogies. (emphases mine)

Most of books on phylogenetic systematics treat analogy as a special case of homoplasy. A good explanation can be found, surprisingly (because he was not a systematicist), in Stephen J. Gould's last book (2002):

We now encounter the logical dilemma that underlies nearly all our exten­sive and lamentable confusion on this issue. Homoplasy and analogy might strike us, at first, as fully synonymous, for both invoke natural selection as the source of separate evolution for similar structures in two lineages. This synonymy certainly applies for convergence. But homoplasy comes in two flavors: parallelism and convergence — with parallelism as the historical root (in Lankester's original definition of homoplasy), but only convergence carry­ing the full flavor of synonymy [...] Unfortunately, a common error of human thinking leads us to define broad and variable categories by their clearest extreme cases. Thus, many scientists have assumed that all homoplasy, whether by parallelism or by convergence, must originate entirely for functional reasons, and not at all by constraint.

Therefore, all analogies are homoplasies, but not all homoplasies are analogies. As suggested by @Remi.b in the comments:

In short, an analogy is a homoplasy caused by convergent evolution. However, a homoplasy not caused by convergent evolution is not an analogy.


Sources:

  • Gould, S. (2002). The structure of evolutionary theory. Cambridge (Mass.): Harvard University Press.
  • Ridley, M. (2011). Evolution. Malden, Mass. [u.a.]: Blackwell.
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  • $\begingroup$ I'm not sure I understand the difference. homoplasy comes in two flavors. I suppose one of them would correspond to an analogy but I don't think the quote says which one. Is a homoplasy due to convergent evolution an analogy while an homoplasy due to parallel evolution is not an analogy? $\endgroup$ – Remi.b Sep 16 '17 at 23:51
  • $\begingroup$ Yes, exactly. It's called just homoplasy, without being called analogy. $\endgroup$ – user24284 Sep 16 '17 at 23:55
  • $\begingroup$ Ok, I get it. You might want to add something like In short, an analogy is a homoplasy caused by convergent evolution but an homoplasy not caused by convergent evolution is not an analogy. because I personally had to read Gould's text 3 times before finding This synonymy certainly applies for convergence, which is the key in knowing what is an analogy. +1 $\endgroup$ – Remi.b Sep 17 '17 at 0:00
  • $\begingroup$ @Remi.b Indeed, Gould's text makes sense if I copy/paste all of it, which is (for that section) some 5 or 6 paragraphs. I thought that it'd be a wall of text, too much for the answer. I'll edit it with your suggestion. $\endgroup$ – user24284 Sep 17 '17 at 0:02
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    $\begingroup$ @user98937 here at Stack Exchange the OP (you) can accept any answer he/she wants, and the accepted answer is nobody's business except OP's. That's out of discussion. However, I'd like to ask you to accept the other answer, because this one is just a complement to that other one. $\endgroup$ – user24284 Sep 17 '17 at 8:46
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This vocabulary is common in textbook but not in the peer-reviewed literature

First please note that while those terms are often used in intro class to evolutionary biology, they are actually rarely used in the peer-reviewed literature.

No trait value is fundamentally derived / ancestral

Note also that any given set of shared trait could be called ancestral or derived depending on the size of the tree that you consider. A trait is therefore not fundamentally ancestral / derived, it depends upon what other trait value you compare it to. Per consequence, it would easier to have a tree under our eyes to discuss these terms.

Note that there is one exception to that. Traits that are shared with LUCA are fundamentally ancestral!

Two states in different lineages can be fundamentally homologous / homoplastic

In general, when we are interest in a given trait, we display a tree so that all homologous trait states appear ancestral. While it is true that homoplastic trait state are necessarily derived when shown, homologous trait state can be shown as derived from a yet more ancestral trait state.

Analogy vs homoplasy

Many think of an analogy as a synonym of homoplasy. However, have a look at @GerardoFurtado's answer for the subtle difference between the two.

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