What animals have evolved the most?

So humans have come quite a long way in the last 5m years or so.

I was wondering though, what species of animal has displayed the most physical change over a similar period, or in a smaller one.

Well, simple logic suggests it would be the species that reproduces the fastest, so there are probably insects that have done a lot “better” than humans, at least in the short term. Typically, though, an animal “evolves” until it reaches a successful niche, and then stays there. Cockroaches got there 300 million years ago, while homo sapiens “maxed out” about 150,000 years ago.

You’d have to define change, though. Do colouration and other trivial traits matter, or does “change” only count when the species can no longer successfully mate with its unchanged “cousin”?

There’s a problem with the premise in the OP. The The genus Homo debuted about 2 (not 5) million years ago. The genus Australopithecus, a different one entirely, is maybe 5 million years old. The species homo sapiens appears to have appeared no more than 300,000 years ago, and hasn’t changed at all over that time. That’s almost the definition of a species.

So asking what species has changed the most physically probably doesn’t have a very good answer.

If you limit the question to mammals, the answer appears to be that the oldest species have evolved the most. That’s because the mutation rate is roughly constant for all mammals:
Study finds Mammalian genomes are mutating at similar rates

While I would agree that mutation rates go hand-in-hand with the pace of evolution, such mutations do not necessarily translate to morphilogical change, which appears to be what the OP is asking. And along those lines, I would agree with Exapno: a species is not going to change substantially in a morphological sense over its temporal span. That is, after all, part of what prompted Eldredge and Gould to develop the theory of Punctuated Equilibrium: periods of stasis (or equilibirum) seen in lineages throughout the fossil record, punctuated by periods of rapid change. And for those that do change in any substantial way morphologically, the result is typically that the new form would be considered a new species.

I’m not sure that is what he’s asking. Would an altered isozyme of alcohol dehydrogenase count, or are we limiting ourselves to mutations that produce obvious outward differences? If the later, then you could miss a speciation event where say, the calcium binding protein inhibitor in seminal fluid changes its binding specificity, and thus messes with fertility between subpopulations of a species.

You’re right that there’s not necessarily a direct translation between mutation and morphological change, regardless of the level of detail you apply to the term. However, Exapno’s claim that Homo Sap hasn’t changed in the last 300,000 years glosses over very real mutations that continue to occur in the species. That’s why I dragged the mutation rate data into the thread.

Yeah, I hate it when that happens!

I’m basing my assumption on the OP’s question, "what species of animal has displayed the most physical change[…]? ". Granted, that may well not be the intended scope of the question. And it is, of course, a different question from that posed in the thread’s title.

As far as I’m concerned, the most important and far-reaching mutation to occur in homo sapiens is the one that allows digestion of lactose throughout adulthood, leading to the dairy industry and all that has implied for the change from hunting and gathering to a fixed abode lifestyle.

However, a physical change that is not. Perhaps the adaptation toward white skin has lead to the largest most recent effects. Is that a physical change? Is it even a mutation?

Nevertheless, if you have any evidence for physical changes in homo sapiens I would be fascinated to read them.