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aknerd
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aknerd
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Evolution!

People LOVE to "debate" evolution. But that's silly, and doesn't really solve anything. If you are in a debate about whether or not evolution is a valid theory, you are either debating someone who has little to no idea what what evolution is, or ARE the person who has little to no idea what evolution is. That doesn't sound like very much fun, so let's not do that, okay?

Instead, this thread will be about topics in evolution, because it is much more entertaining to talk about specific cases and ideas than one big overarching theory. The topics will be chosen by whoever has the best topic, with all "lesser" topics being ignored and forgotten.

Now, I'll start us off with what actually made me want to start this thread: randomness. I was reading Mage's post at the bottom of this thread, and immediately thought about genetic drift.

Here is a classic example of genetic drift in a fruit fly population:

Basically, genetic drift states that random sampling has a lot to do with the evolution of small populations. Think about it: say you have a population of four individuals, two males and two females. One female homozygous allele for blue fur, the others all have a homozygous allele for red fur. Mating between blue and red fur produces a heterzygous purple fur creature. We would therefore expect the next generation to have some purple and red individuals, and the one after that to have all three colors represented. Basic Mendelian stuff.

Now, it gets interesting. Lightening strikes the blue female. She's dead, and will never reproduce. Now, all individuals in this population will be forevermore purely red. Note that this is regardless of the fitness of these genes. Blue fur might have been much more beneficial (perhaps these creatures lived in blue grass, and it provided camouflage), due entirely to random events (as opposed to evolutionary pressures) it is RED fur that becomes fixed in the population.

Going back to and contradicting Mage's comment from before, due to genetic drift, having the same selective factors won't guarantee a particular evolutionary outcome, due to simple random events.

So.... Discuss?

  • 175 Replies
MageGrayWolf
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MageGrayWolf
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Farmer

Don't know if this will drum up any conversation or not but it still seemed interesting.

Genetic study of house dust mites demonstrates reversible evolution

In evolutionary biology, there is a deeply rooted supposition that you can't go home again: Once an organism has evolved specialized traits, it can't return to the lifestyle of its ancestors. There's even a name for this pervasive idea. Dollo's law states that evolution is unidirectional and irreversible. But this "law" is not universally accepted and is the topic of heated debate among biologists. Now a research team led by two University of Michigan biologists has used a large-scale genetic study of the lowly house dust mite to uncover an example of reversible evolution that appears to violate Dollo's law.

..."Parasites can quickly evolve highly sophisticated mechanisms for host exploitation and can lose their ability to function away from the host body," Klimov said. "They often experience degradation or loss of many genes because their functions are no longer required in a rich environment where hosts provide both living space and nutrients. Many researchers in the field perceive such specialization as evolutionarily irreversible."
HahiHa
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HahiHa
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It would be kind of stupid to think a parasite would have to keep it's specialized apparatus even if it's not used anymore. In this aspect, degradation to a state similar to an ancestral one is certainly possible, but to be understood as another adaptation to another environmental change.

It certainly also depends on the genetic background of the structure at hand. If it is interlinked with several other functions and such, it is unlikely to just vanish. If desactivating the expression of such a structure is relatively easy, why not?

Kasic
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Kasic
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Jester

In evolutionary biology, there is a deeply rooted supposition that you can't go home again: Once an organism has evolved specialized traits, it can't return to the lifestyle of its ancestors.


I always took this to mean something along the lines of this: Things don't "unevolve" even if they lose features/traits. It's like a chain, 1+2+3+4, where any change is counted. Even if something evolves some specialized feature and loses it, the organism did not "revert," it responded once more to environmental forces.

Logically, the same environmental forces produce the same changes. Slightly different perhaps, due to the random nature of selection and adaptation, but the same nonetheless. Isn't that why the structure of wings are similar between completely different species? Isn't that why we find strikingly similar behaviors and traits?

I would pose that the dust mites are not reverting or demonstrating reversible evolution. They are simply responding to their environment. Whatever specialized adaptions for living off a host do not matter off the host, and thus eventually die out. Likewise, the ones that are not specially adapted to a host do not flourish as much as the specialized ones and eventually die off.

Evolution is the change of a species over time. Whether such change is changing back to what it was before is irrelevant.

To put it into math terms, evolution is an absolute value. Whether its |1| + |-1|, |1| + |1|, |-1| + |-1|, the answer is always two. A change occurred, whether it added or subtracted a feature. The change is what we're counting.
HahiHa
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HahiHa
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Mage posted this in another thread:

He was a monkey, just like you and me.
But snakes are a subset of the order, Squamata; That means lizard. If snakes evolved from lizards, do they stop being lizards at the moment they become snakes? And when exactly is that moment? It turns out this is another confusing convention in Linnaean taxonomy which is corrected by cladistics. Paraphyletic groups shouldnt exist in phylogenetics, nor would systematic classification permit the emergence of new species to add another equivalent category. Instead existing branches split into successive subsets that are each monophyletic, sharing a common line of descent from which they can diverge but never detach. This means snakes will always be a subset of lizards and apes would still be monkeys.

It is true that Linnaean taxonomy, with classes, orders and all that isn't really used anymore; instead you just speak of a taxon, or taxa (genus and species are still in use due to the scientific names). Thus, "birds" is a taxon within the taxon of "dinosauria".

I don't agree with the conclusions of your post however. Lizards and snakes, together with amphisbaena, are different taxa within the squamata (Squamata does not mean "lizard", but "scaled reptiles&quot. Of course snakes evolved from a lizard-like ancestor, but so did modern lizards.

Our phylogeny is another problem altogether. We are not monkeys, for "monkey" is a paraphyletic group that includes a big part of the primates, but not apes. As you said, paraphyletic groups should not be used in phylogenetic arguments (they're evil :P), so yes, we're primates and we're apes ("apes" being a monophyletic taxon).
Kasic
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Kasic
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Jester

I don't agree with the conclusions of your post however.


Neither do I. They seem to follow the logic of kittens born in the oven being muffins. Simply because something branched off from the same spot at a point in time does not make them forever stuck with the name.
HahiHa
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HahiHa
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Well it depends. It IS important to keep in mind the evolutionary background of the different species. The problem I have with Mages post is that it uses the term "lizard" for modern lizards as well as for the common ancestor of lizards, snakes and amphisbaena. This is essentially using one and the same term twice, in different contexts; for let's not forget that most names of extant animals were given without knowledge of phylogeny (which is for example why the term "reptile" has no significance anymore unless you count in birds). That's why the group containing lizards and snakes is best referred to as squamates, or lizard-likes, rather than lizards.

MageGrayWolf
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Here's the video and transcript that goes along with it. It get's more into explaining why.

Human Evolution: Did We Come From Monkeys?
Turns out we DID come from monkeys!

Basically what it's saying is all the qualities that classify something as a monkey apply to use and other apes. It's not saying something is forever stuck in the classification. It's also saying that the only reason we don't classify humans as monkeys is based on subjective criteria.

"So the only way to properly classify anything is according to the collective characters common to everything already accepted in that category without making exceptions for certain ones."

So what sets us apart?

HahiHa
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HahiHa
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So what sets us apart?

Primarily a number of skeletal and genetical characteristics. If you're arguing that this is subjective, then all phylogenies are.

We didn't evolve from monkeys because "monkeys" (an old colloquial paraphyletic term for the modern animals only) are two branches of the simian tree, old world monkeys and new world monkeys. OWM, NWM and apes evolved more or less separately form a common anthropoid ancestor. It's well possible that there's a bit of a blurry concerning when which group split off, but it's safe to say that both monkeys and apes evolved from a simian (monkey-like, if you want) ancestor.
MageGrayWolf
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MageGrayWolf
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Not willing to concede just yet but I will have to put my argument on hold for the time being due to being very sick and can't focus the way I need to for this. I would appreciate it if someone played devils advocate in my place for the time being so this doesn't die.

We didn't evolve from monkeys because "monkeys" (an old colloquial paraphyletic term for the modern animals only) are two branches of the simian tree, old world monkeys and new world monkeys. OWM, NWM and apes evolved more or less separately form a common anthropoid ancestor.


The argument is that this isn't accurate and we can apply it to the earlier form.
MageGrayWolf
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Found this link (it includes the video previously posted at the end.) It breaks down each point with a conclusion.

http://www.science20.com/genomicron/are_we_descended_monkeys

1. "Apes", as defined as orangutans, gorillas, and chimps, but not humans, is paraphyletic. In other words, either "apes" is not a scientifically defensible term or else it must include humans.

2. "Monkeys" is paraphyletic, and in particular Old World monkeys are more closely related to "apes" than they are to New World monkeys. (Also, humans and Old World monkeys are equally closely related to New World monkeys).

3. We are not descended from any modern "monkeys" or "apes", rather we share common ancestors with them. (In that sense, the answer is NO to whether we're descended from monkeys).

4. The last ancestor shared by all apes (including humans) would itself probably have qualified as an ape. (In that sense, the answer is YES we are descended from an ape, but not any of the modern species).

5. For "monkeys" not to be problematic, it would have to include apes. In that sense, we would be apes AND monkeys. (And, for that matter, we're also lobe-finned fishes). As above, it may very well be that the ancestor of all monkeys and apes (the very bottom node on the phylogeny) would have been considered a monkey, and therefore YES we are descended from a monkey (but again, not any modern species).


I remember coming across information supporting point 4. I will have to look for it again. Though with point 4 we then have to look at the problem that arises mentioned in point 5.
HahiHa
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HahiHa
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Of course apes has to include humans, or else it would be paraphyletic. In that way, yes, monkeys would have to include apes to be monophyletic, in which case we would be apes and monkeys. But the very term monkey is garbage to me, for the simple reason of point 2: OWM are more closely related to apes than to NWM, and as such the name "monkey" makes no phylogenetic sense; it's a relict.

The only way you would be correct is indeed if there would be positive evidence that the common ancestor of NWM, OWM and apes would unite the same characteristics and specializations that make both NWM and OWM. In that case, apes would be derived from actual ancestral monkeys that didn't change much since the anthropoid node; that's quite an assumption.

partydevil
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partydevil
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no ape, no monkey. we came from a fish!!!
(sorry i had to say that)

MageGrayWolf
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MageGrayWolf
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and as such the name "monkey" makes no phylogenetic sense; it's a relict.


That's okay we don't need to use that term, we can use another and still have humans be "monkeys".

Going back to the transcript.
"When referring to basal monkeys, ancestral to ourselves, most scientists prefer to use the word, âAnthropoidâ, one of two acceptable names for that clade. Because â"regardless of phylogeny- scientists generally consider it incorrect, -or even offensive- to refer to humans or other apes as âmonkeysâ. Thatâs a colloquial term, not a scientific one. And itâs paraphyletic, meaning âall anthropoids except apesâ, just like âapesâ used to mean âall hominoids except humansâ. But saying âall of them except for usâ is a Freudian admission that we already know âweâ are one of âthemâ. Besides the words, âanthropoidâ and âhominoidâ both imply possession of human characteristics. So humans could hardly be excluded from either taxon."

The only way you would be correct is indeed if there would be positive evidence that the common ancestor of NWM, OWM and apes would unite the same characteristics and specializations that make both NWM and OWM. In that case, apes would be derived from actual ancestral monkeys that didn't change much since the anthropoid node; that's quite an assumption.


I don't see how that's a huge assumption to make. Or really much of an assumption at all.

"At the root of the simian family tree is another transitional fossil, one that is universally recognized as a monkey and is described as such even by primatologists. Thus this form represents the mother of all monkeys as well as their descendants in denial.

The first division within that clade is between parapithecids, a diverse group of monkeys who are now all extinct, and the clade that remains, forming the next division. Here we have another transitional species bridging the morphological gap between the basal forms of both New World and Old World monkeys."

http://www.biomedcentral.com/1471-2148/8/8/figure/F2?highres=y

Now where would this basal simian which is universally recognized as a monkey happen to fit?
MageGrayWolf
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Sorry here's the image and a apologize for not being able to bring my A game to this.
http://www.biomedcentral.com/content/figures/1471-2148-8-8-2-l.jpg

HahiHa
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But saying âall of them except for usâ is a Freudian admission that we already know âweâ are one of âthemâ.

Not necessarily. There's no reason to think that monkeys stayed unchanged compared to our common ancestor while we obviously didn't. That was my whole point, you were arguing as if we were the only one that changed, but modern monkeys could have changed just as much from that common ancestor.

Besides the words, âanthropoidâ and âhominoidâ both imply possession of human characteristics. So humans could hardly be excluded from either taxon."

Humans are definitely anthropoid; there's not the question at all. The question is, can the basal anthropoid be termed a monkey. It can, you say, and if that fossil really has monkey features, whatever that means, you win

But I still would not say that we are monkeys, as most people will then imagine the modern ones. Best still to use the correct term anthropoids and qualify us as apes, which is more accurate since we're quite derived from the basal node.
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