Freethought & Rationalism Archive

Wargarden · 08-13-2002, 08:41 PM

Someone here might know this. Its probably not too hard, but I don't really know Biology very well.
When is a group, or individual, or species, considered to have evolved into "something else". Is it a classification shift(Kingdom, phyllum, class, order, etc....) at only the species level?

And has this ever been observed?(or does it take so long to change that we haven't had a chance to see it happen since Darwin proposed his theories)

Natural selection seems evident to me because of variation among species. So many different kinds of dogs and cats, but there still a dog and a cat,over time. When is a dog, no, longer a dog? When is a monkey a human?
Certain moths are developing natural tolerances to pollution that others of their same groups are not developing?Is this new tolerance good enough to cause to say its no longer such-and-such a moth(A) and is now such-and-such- a moth(B). BUT ITS STILL A MOTH?!

Evolution= long term natural selection?=divergence of singular species into two similar species(if only one attribute is passed on and on)?

This question has bugged me for awhile. I just wanted to see what others thought or know about it. I don't believe in magic, but this evolution thing is as close as we have to a sane explaination about things we weren't there to see, record, or comment on. I just want to know more about it. I know, read Stephan J. Gould....
thanks,
later

Doubting Didymus · 08-13-2002, 09:39 PM

You would be best of thinking of evolution in terms of a growing bush of twigs, where the twigs diverge at the tips becoming two growing twigs. When part of a species of moth has changed enough so that it no longer breeds with the other part of the species, it is then considered a new species, and is represented in this model by the twig of that species dividing in two. This is the part that has been observed in the laboratory and in the wild.

However, if you think about this model, something can't really move from one branch to another, can it? a twig from the 'cat' branch can never grow into the dog branch and merge into the side of a dog twig. Because of this, no species can ever shift in the taxa that are higher than the species level.

What can happen, however, is for two branches of cat, say at the family level of taxa, to become so different over a great deal of time that it no longer makes sense to call them both 'cats' (I am not sure what taxa the 'cat' description refers to, so from here on I will use humans).

What could happen to the human species in the future is obviously not known for certain, but in theory, it would be possible for the human species to 'speciate', or for the human twig to branch into two. In this case, we would call one species of human 'homo sapiens' and give the other species a new name (probably based on a characteristic), say, 'homo longfingers'.

Now imagine we are even further into the future, and both homo sapiens and homo longfingers have diverged even further into multiple species each. At this point we would all be so closely related that we would all be classified as 'homo' family. However, if this trend continued for a lot longer, biologists (if they were still around after all that time) would eventually classify those species of humans descended from longfingers stock as a different family, probably 'longfingers' family, so that there would be one species 'longfingers longfingers', and also various other species in the longfingers family living alongside the various species of homo. This is what it would take for biologists to classify something as a new family.

To conclude:
The only thing we expect to see in our lifespans 'becoming' something else is at the species level, and this we see all the time.

Biologists would eventually classify a lineage as being a new family, but it would take millions of years before they would consider it.

Nothing ever 'becomes' something else that already exists, such as a modern ape 'becoming' classified a human, but rather, lineages could become entirely new families such as my made up longfingers, over a great deal of time.

By the way, (at the risk of attracting flames), I do NOT suggest you read Gould. He is frequently confusing on certain topics and has a fixation with baseball analogies. Read Dawkins instead.

*Ducks for cover*

Albion · 08-13-2002, 10:59 PM

Quote:

Read Dawkins instead

Especially read "The Blind Watchmaker" and "Climbing Mount Improbable". The latter book makse quite a big deal about how evolution only lets you go up the mountain, not down or across.

Don't be too keen to say things like "but it's still a moth!" Sometimes things are very different even though they look similar. To me, a small brown bird that eats berries and has a migratory lifestyle looks a lot more like a small brown bird that eats insects and grubs and overwinters in cool climates than a terrier looks like a Great Dane, but really the two dog breeds are a great deal more similar.

Species formation has been observed in fish and insects; higher-level changes would take too long. Check out the TalkOrigins site for accounts of species formation:

<a href="http://www.talkorigins.org/faqs/faq-speciation.html" target="_blank">http://www.talkorigins.org/faqs/faq-speciation.html</a>

<a href="http://www.talkorigins.org/faqs/speciation.html" target="_blank">http://www.talkorigins.org/faqs/speciation.html</a>

<a href="http://www.talkorigins.org/faqs/macroevolution.html" target="_blank">http://www.talkorigins.org/faqs/macroevolution.html</a>

Quetzal · 08-14-2002, 12:26 AM

Hey Wargarden!

DD is completely correct. One thing to remember is that every species is made up of a mosaic of different populations (groups of the same species in different places). BTW, this was one of Darwin's key insights - up to that point everybody just assumed that species were homogenous, so it made sense to talk about a species as an immutable group. Anyway, variation is arising almost continuously in these populations (via several different mechanisms). This variation is random in the sense that two different populations won't necessarily (or even probably) get the same variation. As long as the two populations are in contact (i.e., interbreeding), this differential variation usually won't make much difference - the two populations will remain relatively homogenous.

However, suppose these two populations were prevented somehow from interbreeding. Since variation - different variations - are continuously arising in each population, without the leavening action of gene flow, eventually they will become very different. So different that even if they get back in contact somehow, they won't interbreed (not necessarily "can't"). If enough variation exists, then biologists are justified in classifying the two populations as two distinct species - DD's twig branching. We see this today in ring species, among others. This branching, or speciation, can occur (depending on the organism) even in a human lifetime.

The two species continue to diverge from each other - and each one may be subject to further branching. Consider: if two populations of species A diverge into two species A and B, then populations of B ALSO split later into B and C, species C is going to be even MORE different from A than B was. Carry this consecutive branching routine out over enough time, and species ZZ is going to be completely unrecognizable as ever having been related - at first glance - to species A. Only through genetic analysis can they be shown to be distantly related.

To complicate matters further, A and B may have continued to split into new species - just 'cause it happened once doesn't mean the story's over. Moreover, local populations and even species are going extinct all the time. Which of course means that it is often impossible to show direct intermediate linkages between distantly related species or lineages. That's where paleontology, etc comes in. Beyond simply classifying long-dead organisms, paleontology and its related or sub-disciplines play a crucial role in revealing the patterns in the evolution of modern biodiversity. They try and trace backwards in time the lineages of modern organisms to see where they diverged.

Just as an example, paleontologists have discovered that two closely related species of meat eater (of the genus Cimolestes) from way back in the late Cretaceous each gave rise to lineages that ultimately became dogs, cats, bears, weasels, and nearly every other mammalian carnivore on the planet. Here's a speciation event that we can trace - and whose explanation matches that which DD and I gave you - from 70 million years ago that ultimately gave rise to two whoppingly different taxa. Macroevolution indeed!

Obviously this explanation is over-simplified. Hopefully you will at least get the idea how the simple (

) mechanisms of population biology can lead - over time - to the huge diversity of life on Earth. Scientists really aren't talking out their butts when they talk about so-called macroevolution. It's the creationists who are either deliberately or through ignorance misunderstanding how it works. The only a priori assumption in the whole affair is that processes that we observe today worked the same way (or close enough) in the distant past.

Hope this answers your question.

abe smith · 08-14-2002, 04:54 AM

A good place to start wd be w/ two recent works of Ernst Mayr; titles: *What Is Biology* (?) and *What Evolution Is*. A quick way to define the term "species" (both singular & plural) = the down & dirty definition may be that members/individual members of a species are capable of reproducing together to produce viable & fertile progeny. (Why horses & donkeys are different species >>> they don't. = Mules are sterile.) Why not take some beginning Biology courses, Person/Inquirer? Or more simply, go to your local college library & ask the ref librarian to lend you some recent introductory texts. Bon voyage! & welcome to our midden! Abe

Wargarden · 08-17-2002, 12:52 PM

hey folks,
Thanks a bunch. Sorry I've been away from the nearest terminal access for a few days. Awsome answers! A friend of mine also said once a memeber of a species can't successfully mate with a partner of the same species, you say it evolved.
(but what about bacterica and viruses and fungi,etc...).By the way, the "its still a moth" was a Creationist rebutle that had stumped me. Just the depth of inquiry i guess, and you guys have MUCH MORE depth than that guy.
Anyway, thanks again.
Rock!

Mageth · 08-17-2002, 01:06 PM

A friend of mine also said once a memeber of a species can't successfully mate with a partner of the same species, you say it evolved.

Well, actually, they would no longer be the same species. And individual members of a species don't evolve into different species; populations do.

08-13-2002, 08:41 PM	#1
Wargarden Junior Member Join Date: May 2001 Location: Earth; Sol Posts: 37	question for the taking Someone here might know this. Its probably not too hard, but I don't really know Biology very well. When is a group, or individual, or species, considered to have evolved into "something else". Is it a classification shift(Kingdom, phyllum, class, order, etc....) at only the species level? And has this ever been observed?(or does it take so long to change that we haven't had a chance to see it happen since Darwin proposed his theories) Natural selection seems evident to me because of variation among species. So many different kinds of dogs and cats, but there still a dog and a cat,over time. When is a dog, no, longer a dog? When is a monkey a human? Certain moths are developing natural tolerances to pollution that others of their same groups are not developing?Is this new tolerance good enough to cause to say its no longer such-and-such a moth(A) and is now such-and-such- a moth(B). BUT ITS STILL A MOTH?! Evolution= long term natural selection?=divergence of singular species into two similar species(if only one attribute is passed on and on)? This question has bugged me for awhile. I just wanted to see what others thought or know about it. I don't believe in magic, but this evolution thing is as close as we have to a sane explaination about things we weren't there to see, record, or comment on. I just want to know more about it. I know, read Stephan J. Gould.... thanks, later

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

08-13-2002, 09:39 PM	#2
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	You would be best of thinking of evolution in terms of a growing bush of twigs, where the twigs diverge at the tips becoming two growing twigs. When part of a species of moth has changed enough so that it no longer breeds with the other part of the species, it is then considered a new species, and is represented in this model by the twig of that species dividing in two. This is the part that has been observed in the laboratory and in the wild. However, if you think about this model, something can't really move from one branch to another, can it? a twig from the 'cat' branch can never grow into the dog branch and merge into the side of a dog twig. Because of this, no species can ever shift in the taxa that are higher than the species level. What can happen, however, is for two branches of cat, say at the family level of taxa, to become so different over a great deal of time that it no longer makes sense to call them both 'cats' (I am not sure what taxa the 'cat' description refers to, so from here on I will use humans). What could happen to the human species in the future is obviously not known for certain, but in theory, it would be possible for the human species to 'speciate', or for the human twig to branch into two. In this case, we would call one species of human 'homo sapiens' and give the other species a new name (probably based on a characteristic), say, 'homo longfingers'. Now imagine we are even further into the future, and both homo sapiens and homo longfingers have diverged even further into multiple species each. At this point we would all be so closely related that we would all be classified as 'homo' family. However, if this trend continued for a lot longer, biologists (if they were still around after all that time) would eventually classify those species of humans descended from longfingers stock as a different family, probably 'longfingers' family, so that there would be one species 'longfingers longfingers', and also various other species in the longfingers family living alongside the various species of homo. This is what it would take for biologists to classify something as a new family. To conclude: The only thing we expect to see in our lifespans 'becoming' something else is at the species level, and this we see all the time. Biologists would eventually classify a lineage as being a new family, but it would take millions of years before they would consider it. Nothing ever 'becomes' something else that already exists, such as a modern ape 'becoming' classified a human, but rather, lineages could become entirely new families such as my made up longfingers, over a great deal of time. By the way, (at the risk of attracting flames), I do NOT suggest you read Gould. He is frequently confusing on certain topics and has a fixation with baseball analogies. Read Dawkins instead. Ducks for cover

08-14-2002, 12:26 AM	#4
Quetzal Senior Member Join Date: Nov 2001 Location: Ecuador Posts: 738	Hey Wargarden! DD is completely correct. One thing to remember is that every species is made up of a mosaic of different populations (groups of the same species in different places). BTW, this was one of Darwin's key insights - up to that point everybody just assumed that species were homogenous, so it made sense to talk about a species as an immutable group. Anyway, variation is arising almost continuously in these populations (via several different mechanisms). This variation is random in the sense that two different populations won't necessarily (or even probably) get the same variation. As long as the two populations are in contact (i.e., interbreeding), this differential variation usually won't make much difference - the two populations will remain relatively homogenous. However, suppose these two populations were prevented somehow from interbreeding. Since variation - different variations - are continuously arising in each population, without the leavening action of gene flow, eventually they will become very different. So different that even if they get back in contact somehow, they won't interbreed (not necessarily "can't"). If enough variation exists, then biologists are justified in classifying the two populations as two distinct species - DD's twig branching. We see this today in ring species, among others. This branching, or speciation, can occur (depending on the organism) even in a human lifetime. The two species continue to diverge from each other - and each one may be subject to further branching. Consider: if two populations of species A diverge into two species A and B, then populations of B ALSO split later into B and C, species C is going to be even MORE different from A than B was. Carry this consecutive branching routine out over enough time, and species ZZ is going to be completely unrecognizable as ever having been related - at first glance - to species A. Only through genetic analysis can they be shown to be distantly related. To complicate matters further, A and B may have continued to split into new species - just 'cause it happened once doesn't mean the story's over. Moreover, local populations and even species are going extinct all the time. Which of course means that it is often impossible to show direct intermediate linkages between distantly related species or lineages. That's where paleontology, etc comes in. Beyond simply classifying long-dead organisms, paleontology and its related or sub-disciplines play a crucial role in revealing the patterns in the evolution of modern biodiversity. They try and trace backwards in time the lineages of modern organisms to see where they diverged. Just as an example, paleontologists have discovered that two closely related species of meat eater (of the genus Cimolestes) from way back in the late Cretaceous each gave rise to lineages that ultimately became dogs, cats, bears, weasels, and nearly every other mammalian carnivore on the planet. Here's a speciation event that we can trace - and whose explanation matches that which DD and I gave you - from 70 million years ago that ultimately gave rise to two whoppingly different taxa. Macroevolution indeed! Obviously this explanation is over-simplified. Hopefully you will at least get the idea how the simple ( ) mechanisms of population biology can lead - over time - to the huge diversity of life on Earth. Scientists really aren't talking out their butts when they talk about so-called macroevolution. It's the creationists who are either deliberately or through ignorance misunderstanding how it works. The only a priori assumption in the whole affair is that processes that we observe today worked the same way (or close enough) in the distant past. Hope this answers your question.

08-14-2002, 04:54 AM	#5
abe smith Veteran Member Join Date: Apr 2001 Location: springfield, MA. USA Posts: 2,482	A good place to start wd be w/ two recent works of Ernst Mayr; titles: What Is Biology (?) and What Evolution Is. A quick way to define the term "species" (both singular & plural) = the down & dirty definition may be that members/individual members of a species are capable of reproducing together to produce viable & fertile progeny. (Why horses & donkeys are different species >>> they don't. = Mules are sterile.) Why not take some beginning Biology courses, Person/Inquirer? Or more simply, go to your local college library & ask the ref librarian to lend you some recent introductory texts. Bon voyage! & welcome to our midden! Abe

08-17-2002, 12:52 PM	#6
Wargarden Junior Member Join Date: May 2001 Location: Earth; Sol Posts: 37	hey folks, Thanks a bunch. Sorry I've been away from the nearest terminal access for a few days. Awsome answers! A friend of mine also said once a memeber of a species can't successfully mate with a partner of the same species, you say it evolved. (but what about bacterica and viruses and fungi,etc...).By the way, the "its still a moth" was a Creationist rebutle that had stumped me. Just the depth of inquiry i guess, and you guys have MUCH MORE depth than that guy. Anyway, thanks again. Rock!

08-17-2002, 01:06 PM	#7
Mageth Contributor Join Date: Jul 2001 Location: Deep in the heart of mother-lovin' Texas Posts: 29,689	A friend of mine also said once a memeber of a species can't successfully mate with a partner of the same species, you say it evolved. Well, actually, they would no longer be the same species. And individual members of a species don't evolve into different species; populations do.

Freethought & Rationalism Archive

The archives are read only.