Use of the term "evolution"

[PhDwannabe]

Hey all:

 

I'll start by saying that I'm not utterly ignorant of evolutionary biology--I suppose I have a college-intro-level knowledge of it, and do not subscribe to any particularly goofy theories regarding it.

 

I am aware that the creationists/IDers point to examples of natural selection at work and scream that this isn't evolution, just adjustments in the gene pool, changing frequencies of traits, etc. The example of peppered moths in industrial Britain, I know, has attracted no shortage of hoarse screams. My question is, according to current definitions (or perhaps just current norms) that you might be more in step with than I am, when is it conventional to say that one creature has "evolved from" another?

 

The example of dogs is the big one in my mind--they're just domesticated gray wolves, subjected to the selection pressures of 10,000+ years of yummy trash sitting around the outskirts of human settlements. As far as I'm aware, they're fully sexually compatible with wild gray wolves. Would it be conventional to refer to the recent "evolution" of dogs, or say that they have recently "evolved from" wild gray wolf stock? Or do you really need speciation to use the e-word? It'd be helpful if those with up-to-date contact with the evolutionary bio world could share their thoughts.

 

 

Thanks,

DJ

[CharonY]

In the simplest definition evolution is the process resulting in gene pool composition. As such you could take any two populations and try to make evolutionary inferences. Speciation is merely one special (and slightly arbitrary) event.

However, extant species generally have not evolved from each other. Dogs and wolves share common ancestors and while dogs (as a subpopulation) have diverged differently, the gene pool in current wolves will have diverged from the original stock as well (albeit presumably at a lower rate).

 

To use the term evolved you would walk back in time and trace the phylogeny of ancestors.

[Mr Skeptic]

when is it conventional to say that one creature has "evolved from" another?

 

When the two creatures are are not on different branches of the phylogenetic tree.

[PhDwannabe]

However, extant species generally have not evolved from each other. Dogs and wolves share common ancestors and while dogs (as a subpopulation) have diverged differently, the gene pool in current wolves will have diverged from the original stock as well (albeit presumably at a lower rate).

 

To use the term evolved you would walk back in time and trace the phylogeny of ancestors.

 

My question still remains: when is it enough? How far back do you have to walk to use the term? Do you need to walk back in time across a species barrier? I was using some shorthand in my original question which I shouldn't have, which you needled in on a bit, so I'll clarify: could we say that, in the last 10-15 thousand years, dogs have evolved from recent ancestors which are very much like extant gray wolves? Or, since extant canis lupus, extant canis lupus familiaris, and 10-15kya canis lupus could probably cross in any combination to create fertile offspring, is it inappropriate to use the word "evolved" in the bolded phrase above?

[CharonY]

There is no time limit, that is the point. It is all contextual. It all depends on where you draw the boundaries for a given population and what you want to discuss. The reason is that evolution is a smooth function and does not naturally lead to discrete boundaries. Species is just something that we added to create structure in phylogeny. In other words, it depends on the context you want to describe whether the term evolved is correct, or not.

For instance, it is mostly correct for the most part to state (as above) that the current wolf and dog populations have evolved from a common population ("ancestor" is mostly used in situations where speciations occured).

There are exceptions, however. Dogs and wols are still able to reproduce and the above description would be inaccurate to apply to this offspring.

To summarize, the term evolved is used to describe the history of a given population or the phylogenetic history of given populations. The accuracy is determined by how strong the boundaries between the populations are. Species would be on the one end (very strong) anything below that would be fuzzier and context-dependent.

[Mr Skeptic]

Ah, so the question is where is the line between ancestry and evolution? There isn't really one. You could say it is when the ancestor and descendant are different species, but there is no dividing line between two species. So really its up to personal preference.

[PhDwannabe]

Excellent responses, gentlemen. Just what I was asking for. Thanks! Anyone else is of course free to add something, were there to be anything more to add.

[Asyncritus]

Excellent responses, gentlemen. Just what I was asking for. Thanks! Anyone else is of course free to add something, were there to be anything more to add.

 

There's a great deal of latitude (I suppose some cranks would say ' wide semantic range') in the use of the term 'evolution'.

 

Biologically speaking, the word is used to describe the fact that there is 'variation' between individuals of the same species, then extended to such things as 'ring species', and to the limited amount of speciation that has been observed to occur (usually where there is a considerable amount of forced inbreeding, such as happened in the Hawaiian islands. Darwin's finches are a good example of this. There are all sorts of beak shapes and sizes in the 'finch' group, which resulted in the classification of several species as species. All this probably resulted from inbreeding in the restricted area of the Galapagos islands. Gould, for example calls this 'reproductive isolation'.

 

This is called 'evolution', and to that limited extent, it is obviously valid.

 

It is when we attempt to extrapolate these extremely scarce, and highly limited (numerically speaking) examples into accounting for the existence of the zillion or so species which existed in the past, and exist today, that the term 'evolution' runs into severe difficulties.

 

I imagine what most people would think of when they use or hear the word 'evolution' in a biological context is something like the way fishes evolved into tetrapods, or reptiles into birds: both of which are alleged to have taken place despite the astronomical difficulties involved.

 

To overcome these astronomical difficulties, the 'long time' explanation is given - as if length of time can make the impossible possible.

 

Dawkins, for example, describes the bats in 'The God Delusion' quite splendidly, and in a manner worthy of any creationist. He points out the sheer magnificence of their echolocating systems, saying words to the effect that biophysical engineers would a. envy, and b. be extremely hard put to duplicate such systems. He's right - because even today, the US military and doubtless others, are busy trying to copy the bats' echolocating systems, so far superior are they to the current US technology, and we all know how deadly and effective those are!

 

So you pays your money, and takes your choice. Limited 'evolution' - or unlimited optimism?

[CharonY]

There is almost nothing accurate in the post above, starting with the definition of evolution. Evolution describes a process and hence does not merely describe existing variation. Things deteriorate from there.

[PhDwannabe]

I imagine what most people would think of when they use or hear the word 'evolution' in a biological context is something like the way fishes evolved into tetrapods, or reptiles into birds: both of which are alleged to have taken place despite the astronomical difficulties involved.

 

To overcome these astronomical difficulties, the 'long time' explanation is given - as if length of time can make the impossible possible.

 

I think evolutionary biology does more than "give a 'long time' explanation." I think it also describes the methods by which these changes occur, the environmental pressures which drive them, and the dump trucks upon dump trucks of morphological, genetic, and paleontological evidence for their occurrence. I, uh, I think.

[dragonstar57]

correct me if I am wrong but it seems that he is asking when it is it time to say call a certain group of animals in a species no longer part of that species but a new species entirely

[kitkat]

correct me if I am wrong but it seems that he is asking when it is it time to say call a certain group of animals in a species no longer part of that species but a new species entirely

 

The perfect time is now that is seen in the sea slug that eventually will have the entire chloroplast as part of its DNA make-up. Evolution occurring right in front of your very own eyes. I hope science is documenting every step in mutation changes in the sea slug. Perhaps the sea slug is the template for this new innovation and in the future maybe there will be more species able to use it. After all, isn't our sun suppose to get hotter in the future?

[Maximus Semprus Veridius]

Well technically the term "evolution" just means change, obviously though you mean "E by the M O Natural S" (see my little rap there?) Well im not sure if there is a definate absolute term tbh but I think most people would say when they can't produce off-spring that can breed. I think the question that would come in handy to answering your own question would be "what is a species?" maybe?