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Evolution

Posted Feb 25, '13 at 3:39am

HahiHa

HahiHa

5,305 posts

Knight

I don't know if I'd say that... Indeed, one of the main reasons that biologists still place them into different species is due to the fact that neither one of them can survive in the other's environment for very long. If you raise a polar bear in a brown bear's habitat, it'll still have white, insulating fur, and (relatively) smaller, sharper carnivorous teeth. While they do and can interbreed, this is hardly a common event. And when you look at the morphological and dietary differences (as Mage said), there are some pretty severe distinctions between the two groups.

The zone between both habitats are habitable by both, and who's to say polar bears wouldn't eat berries if they could? Dietary differences are obviously more due to the different environment. The fur isn't much of a big deal either, think of the stoat for example. Polar bears are just at a more permanent stage. And please, what morphological differences do you mean? Anyway, as Mage said, I think they're better called a subspecies than a different species.

That's really the problem with the reproduction-isolation definition of speciation.

It's not the only species definition. There are morphological definitions, reproductive definitions, phylogenetic definitions, and in the end the best is a blend of them all. Depends what is available, leading to the enxt point:

But even more than that, there is another huge problem with this definition: what about fossils?

For fossils of course, until now mostly morphological information was taken; usually teeth morphology in mammals. We're starting to get DNA material from recent fossils, and for the old ones, there are still other methods like bone histology (yes, bone microstructure is often preserved even though the original materials have been exchanged by minerals).

But another point in fossils is, usually the fossils we find are so distinctly different from others, due to the fragmentary report, that defining species isn't as hard as in recent fossils like for hominids, where we have a huge mash of fossils and no clear idea of where to put boundaries.

What about bacteria, some of which can directly incorporate the DNA from similar organisms (though not necesarily from the same species) right into their own code? This throws a serious monkey wrench into the problem, as they can hybridize without reproducing. Which is really cool, but also makes things rather complicated.

Don't they just exchange plasmids during bacterial sex? Nuclear information is spread solely through asexual reproduction, i.e. splitting. It does influence evolution, but is not much of a species issue. I think.

Thinking about it I wonder if ultimately some form of gradient might be necessary, rather than a set definition.

That's exactly the problem they have in paleoanthropology. Everyone that finds a new fossil makes a new species out of it, and in the end we have a heap of species and no clear order. A gradient would be the more sensible thing in that aspect, as biologically speciation is indeed a gradual event, but tell that to those fame-hunting professors -.-

To answer your previous question on gradualism vs punctualism, you'll have noted from above I'm rather for gradualism, though I don't exclude punctualism. I think every taxa have a sort of base evolutionary adaptive rate, depending on the metabolism, environment etc. etc., with a more or less high potential to accomodate to fast changes. So in events when the environment changes quickly, those with a high potential rate may adapt fast, making it look seemingly saltatory in the fossil record. What I completely reject is pure saltatorism. Organisms change constantly, even though the changes can be infinitesimal; example: coelacanths. They look almost exactly like their fossil ancestors, and yet they're different species; the fossil species are extinct, the modern ones just look like them.
 

Posted Feb 25, '13 at 5:28am

HahiHa

HahiHa

5,305 posts

Knight

There are morphological definitions, reproductive definitions, phylogenetic definitions,

And how could I forget the molecular/genetic definitions, increasingly gaining importance.

On the species issue, there's another fun thing: ring species. It's basically a geographical chain of subpopulations that at its two "ends" cannot interbreed anymore.
 

Posted Feb 25, '13 at 7:08pm

aknerd

aknerd

1,431 posts

who's to say polar bears wouldn't eat berries if they could?

Being able to eat berries and being able to survive off a diet largely consisting of nuts and berries are two completely different things. The polar bear's skull is low and flat, which is good for swimming, but also provides poor support for chewing. This means they have a hard time mechanically breaking down plant matter. They also don't chew through bones the way brown bears do, but just tear off chunks of meat with their smaller, sharper teeth and swallow it whole. In terms of other morphological differences, well, here's a grizzly bear and a polar bear who were both raised in captivity at the same zoo from the same age:
http://3.bp.blogspot.com/_SV49XCNN4JU/TRzFWdtXOEI/AAAAAAAASy4/2OjZSxMN-Qw/s1600/AlaskaZooBear.standalone.Bobhallinen1998oreoahpun.jpg

Here's some fun stuff about skulls.

(yes, bone microstructure is often preserved even though the original materials have been exchanged by minerals).


Well, here's the problem with that. Most things don't have bones. Really if you think about it, hardly anything has a skeleton when you look at all organisms since the beginning of life. The first chordates didn't evolve until around 525 millions years ago, whereas the earliest fossils come from around 3.5 billion years ago. And then, we have plants, brachiopods, echinoderms, arthopods, etc. The most common (large) fossils are those of shells, many of which are simply molds or casts and never consisted of any actual organic matter. So, we want to get an idea pre-cambrian species diversity, we need to look at morphology. Oh, and TIME. As you hinted to later, by dating fossils we can sometimes get some information about speciation.

due to the fragmentary report, that defining species isn't as hard as in recent fossils like for hominids

Oh... I don't know about that. Especially when you get into pollen analysis... Fossilized pollen is a real pain.


Don't they just exchange plasmids during bacterial sex? Nuclear information is spread solely through asexual reproduction, i.e. splitting. It does influence evolution, but is not much of a species issue. I think.


Well... some bacteria can incorporate plasmids into their nuclear DNA, and can make plasmids from their nuclear DNA as well. So, it really messes things up. Think about it: the lineage of a bacterial organism is not fixed. And, they can trade plasmids between what we currently think of as different species. But as you noted, they don't trade their whole "genome"*, just parts of it. Speciation, really, is all about relatedness. Intuitively, we want members of one species to be more related (be it genetically, morphologically, or otherwise) to all members of its own species than to a member of another species. But the relation between bacterial organisms is constantly in flux: an individual might incorporate DNA that makes it more related to a member of a different species than it is to its own "siblings" or original parent(s). So yeah, pretty complicated.

The whole species problem is a massive tangle that really isn't even -that- important.


The thing is, we need to have some basic unit for measurement's sake. Specifically, we need to be able to measure species diversity in a consistent manner, so we can compare diversity between different areas and different times. This is why the fossil problem is such a... problem. If we define species for fossils in a different way than we do for extant species, we can't compare current diversity to past diversity.
 

Posted Feb 26, '13 at 2:24am

HahiHa

HahiHa

5,305 posts

Knight

Most things don't have bones.

I know, I just said this is a good way to analyze vertebrates. And shells. Shell microstructure can also give data.

Oh... I don't know about that. Especially when you get into pollen analysis... Fossilized pollen is a real pain.

Oh well... again, I had mostly vertebrates in mind, and older fossil imprints of invertebrates. But that is only half true, as with some vertebrates we do have trouble classifying them. And as soon as a previously unknown skull comes up, things change again :P
 

Posted Mar 5, '13 at 10:20pm

aknerd

aknerd

1,431 posts

So it would seem as though we need a change in topics.

I suggest... HUMAN EVOLUTION. Mainly because I know people on here know a lot more about this subject than I do (I'm more into trees and such), and thus maybe I'll learn something.

So, to start us off, lets talk about about beer. Beer (well... alcohol) is a poison... and yet we can drink it. In relatively large quantities, even. From what I've heard, the going theory is that alcohol kills bacteria, making water safer to drink, thus increasing the fitness of those able to process alcohol.

This makes sense, except... isn't alcohol, you know, dehydrating? I mean, its a diuretic, right? So how can one survive exclusively drinking alcoholic beverages?

 

Posted Mar 5, '13 at 10:35pm

aknerd

aknerd

1,431 posts

Oh, woops, I forgot to add this: Some cultures (native Alaskans, aborigines, etc) historically did not really consume alcohol. And indeed, these cultures tend to have way higher rates of alcoholism. So, there seems to be a genetic factor linked to alcoholism (which I think is well known). So, kind of going off of this example, how does human evolution play into societal needs? Think about it this way. Alcohol is a poison. But, some cultures have adapted to this poison to such an extent that consuming it is very much a non-issue, while others have not adapted to it at all and it can have drastic effects.

But, because the group that did adapt to the poison makes up a majority in certain areas, and enjoys the consumption of the poison, they make the poison widely available to everyone. Even to those to whom it is still, well, poisonous. Is that okay?

I don't know. I feel like we shouldn't withhold goods or services based on evolutionary backgrounds, because, well, that would/could be more than a little racist. But on the other hand, it seems weird to have one set of restrictions (or lack thereof) on the sale of a substance that effects different groups very differently.

 

Posted Mar 6, '13 at 3:07am

HahiHa

HahiHa

5,305 posts

Knight

Alcohol is still poisonous to everyone. And no animal ever drank only fermented beverages, to my knowledge; that is physiologically not feasable. Just thought I'd state this to avoid misunderstandings.

What I know is that honey, being a good conservation medium as it does not spoil, was used to keep food consumable, and over time it may have fermented, leading to the invention of mead.

Essentially I think it all originates from fermentation of certain goods, and the realization it made you dizzy. There are certain parrots that are known to eat fermented fruits to such an amount as to get real wasted, fall on the floor and not able to fly. Tell me what is their selective advantage?

I'm actually not convinced alcohol has any advantage. It does help conserve food, but it's consumption is mostly due to it being a neural toxin, making us feel dizzy and good. It's more of a side-effect than a real advantage. Convenience, so to say.

 

Posted Mar 6, '13 at 6:42pm

pangtongshu

pangtongshu

9,761 posts

I'm actually not convinced alcohol has any advantage.


With limited quantities..it is good for the heart. The most common way is with a glass of whine (just one) because of some of it's qualities..but one cup of beer is also beneficial

Wine

Beer
 

Posted Mar 7, '13 at 1:39am

HahiHa

HahiHa

5,305 posts

Knight

The most common way is with a glass of whine (just one) because of some of it's qualities..

I have seen studies that claim the contrary. But I agree that small quantities certainly aren't bad. Question is, is the beneficial effect, if present, big enough to actually make a difference in our evolution?
 

Posted Mar 7, '13 at 4:09pm

pangtongshu

pangtongshu

9,761 posts

Question is, is the beneficial effect, if present, big enough to actually make a difference in our evolution?


There may be a possibility of it already having done so
 
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