Evolution Question

[cre8ivmind]

After having an education in Zoology, and with my general interest in the natural sciences, I am an ex-creationist. I have a question about evolution. I have heard it said that chimpanzees and humans are closer related to each other than horses and zebras, and to lions and tigers. If this is true, than why is it that the latter two pairs of creatures can interbreed, but humans and chimps can't?

 

Thanks.

[ydoaPs]

After having an education in Zoology, and with my general interest in the natural sciences, I am an ex-creationist. I have a question about evolution. I have heard it said that chimpanzees and humans are closer related to each other than horses and zebras, and to lions and tigers. If this is true, than why is it that the latter two pairs of creatures can interbreed, but humans and chimps can't?

 

Thanks.

 

I don't remember hearing of anyone trying to mate with a chimp.

[cre8ivmind]

I don't remember hearing of anyone trying to mate with a chimp.

 

I've heard of an experiment where someone artificially inseminated female chimps, but it didn't work.

[D H]

What makes you think they can't?

 

From http://news.scotsman.com/uk/Exclusive-Should-we-beware-the.4028970.jp:

29 April 2008

A LEADING scientist has warned a new species of "humanzee," created from breeding apes with humans, could become a reality unless the government acts to stop scientists experimenting. ... Leading scientists say there is no reason why the two species could not breed, although they question why anyone would want to try such a technique.

[Daecon]

I have heard it said that chimpanzees and humans are closer related to each other than horses and zebras, and to lions and tigers. If this is true...

 

Maybe it isn't true?

 

Besides, do lions & tigers, or donkeys & horses, have the same number of chromosomes each?

 

I suspect that the specific chromosomes that are different in each case to play a factor to the success of crossbreeding.

[Mr Skeptic]

I don't remember hearing of anyone trying to mate with a chimp.

 

I'm guessing that not only has this been done, but videoed and put on the internet. People have all sorts of fetishes. That is unlikely to result in a "humanzee" because we have different number of chromosomes, among other reasons.

[ydoaPs]

we have different number of chromosomes, among other reasons.

LIES!

 

Our Chromosome 2 is actually two fused chromosomes.

[Vexer]

Actually, the whole "interbreeding" thing is much more murky than one might suppose.

 

Yesterday I heard how two different species of frog interbred.

 

I though that 'species' are a definition of what can't interbreed?

[pioneer]

Here is my take on this. All the dynamic components within cells work because of hydrogen bonding. This defines the secondary and tertiary structures of all the macro-molecules that makes everything possible, from enzymes, to the DNA double helix, to the chromosomes. That being said, the chromosomes define a certain configurational potential or their composition plus their shape is sort of block of potential at the level of the hydrogen bonding.

 

When the female gamete cell forms it is using a species dependant DNA, with the bulk ovum, a type of extended configuration that is in hydrogen bonding equilibrium with that DNA. When we add male DNA, the ovum's bulk grid and the combined DNA need to form a close equilibrium configurational match. The gene shuffling is heading toward equilibrium. It falls short, slightly, so there is potential to keep moving toward equilibrium.

 

If the final shuffle is out of whack, it can't the get going because the DNA and cytoplasm are just too far out of configurational equilibrium. What this suggests is one should be able to combine odd species, but one would need to add DNA configurational binder to compensate for non-equilibrium. This is easier said than done, without knowing how to configure.

[cre8ivmind]

I forgot to mention... Linnaean (sp.?) classification seems to imply that chimps and humans are not as related to each other as lions and tigers, or horses and donkeys. Our genus name is different from the chimps, unlike the other two pairs of creatures:

Chimps & us:Pan troglodytes and Homo sapiens

Lion & Tiger: Panthera leo and Panthera tigris

Horse & Donkey: Equus caballus and Equus asinus

[Paralith]

I though that 'species' are a definition of what can't interbreed?

 

The definition of the word "species" has been a long standing issue in biology. It's hard to find a biologically meaningful definition that applies to every single case. However, the most commonly used definition is that different species don't interbreed for one reason or another - it might be a physical inability to mate and/or result in viable offspring, or it may be that they are environmentally separated, or that there are behavioral differences in mating that prevent it. In the latter two cases, the two species might be technically capable of producing crossbred offspring, but in natural conditions would not interbreed on their own.

 

This failure to interbreed results in a barrier to gene flow between the two populations which then allows them to diversify from each other, which is a generally important requirement for speciation.

 

As for the OP, the ability to interbreed is not a good measure of relatedness. While there are less genetic differences between humans and chimps than there are between horses and zebras, one of those differences between humans and chimps has resulted in a chromosome change that highly reduces the chances of producing viable offspring between the two. Horses and zebras have many more differences, but none of those differences have resulted in a change of that nature.

 

I forgot to mention... Linnaean (sp.?) classification seems to imply that chimps and humans are not as related to each other as lions and tigers, or horses and donkeys. Our genus name is different from the chimps, unlike the other two pairs of creatures:

Chimps & us:Pan troglodytes and Homo sapiens

Lion & Tiger: Panthera leo and Panthera tigris

Horse & Donkey: Equus caballus and Equus asinus

 

At the time such names were assigned to these species, evolutionary theory was much less well understood and implemented. Not to mention the general desire to put humans on a separate, special level above other animals. I personally think the classifications should be adjusted to better reflect phylogenetic reality.

[Mr Skeptic]

At the time such names were assigned to these species, evolutionary theory was much less well understood and implemented. Not to mention the general desire to put humans on a separate, special level above other animals. I personally think the classifications should be adjusted to better reflect phylogenetic reality.

 

I personally think that that will be met with incredible resistance and/or hostility from the religious, the average joe, some of the biologists, and the folks from the legal system. Basically, it would piss off almost everyone, and for little reason. And for whatever reason, the tiny biological difference between Homo and Pan has resulted in tremendous differences in actuality -- high technology and communications -- not seen in any other species. Not to mention bipedalism and furlessness. So it wouldn't be completely accurate to place ourselves with the apes, despite the biological similarities. It may be better to just teach students that we're very similar, rather than rename us.

[Paralith]

I personally think that that will be met with incredible resistance and/or hostility from the religious, the average joe, some of the biologists, and the folks from the legal system. Basically, it would piss off almost everyone, and for little reason. And for whatever reason, the tiny biological difference between Homo and Pan has resulted in tremendous differences in actuality -- high technology and communications -- not seen in any other species. Not to mention bipedalism and furlessness. So it wouldn't be completely accurate to place ourselves with the apes, despite the biological similarities. It may be better to just teach students that we're very similar, rather than rename us.

 

I'm sure some people will highly dislike it. But as I understand the current theory, classification should accurately represent phylogeny, and phylogeny is a description of genetic relatedness, not phenotypic similarity. Phylogenetically, it is completely accurate to place ourselves with the apes. To change the rule for humans just because some people don't like it and most people still like to think of humans as more different and special than other animals is simply bad scientific practice and not one that I think should be taught to students.

[CharonY]

To change the rule for humans just because some people don't like it and most people still like to think of humans as more different and special than other animals is simply bad scientific practice and not one that I think should be taught to students.

 

Hear hear.

[Mr Skeptic]

I'm sure some people will highly dislike it. But as I understand the current theory, classification should accurately represent phylogeny, and phylogeny is a description of genetic relatedness, not phenotypic similarity. Phylogenetically, it is completely accurate to place ourselves with the apes. To change the rule for humans just because some people don't like it and most people still like to think of humans as more different and special than other animals is simply bad scientific practice and not one that I think should be taught to students.

 

I think that most people like to think of humans as more different and special than other animals because we are different and special compared to them. Not genetically, though. You're right, I was thinking phenotypes, not genetics.

 

And I wasn't thinking of a permanent change in the rules, just a temporary exception. While it is scientifically admirable to do the scientific thing regardless of the consequences, it may not be a clever thing to do. Most of the public is not aware of this debate, nor will know the reason for the change. If there is even a shred of doubt, or legitimate biologists who disagree, that will be the focus of the media. And we're not at a particularly good time for atheists and Christians to get along.

[Paralith]

Most of the public is not aware of this debate, nor will know the reason for the change. If there is even a shred of doubt, or legitimate biologists who disagree, that will be the focus of the media. And we're not at a particularly good time for atheists and Christians to get along.

 

I do not at all think that science should at any time make sacrifices simply so ignorant people won't get their panties in a knot. But that's just my opinion.

[PhDP]

I'm sure some people will highly dislike it. But as I understand the current theory, classification should accurately represent phylogeny, and phylogeny is a description of genetic relatedness, not phenotypic similarity. Phylogenetically, it is completely accurate to place ourselves with the apes. To change the rule for humans just because some people don't like it and most people still like to think of humans as more different and special than other animals is simply bad scientific practice and not one that I think should be taught to students.

 

I don't want to be picky but... I agree with everything except that part; phylogeny is a description of genetic relatedness. Phylogeny is a description of evolutionary relatedness. Genetic relatedness is used as a mean to understand evolutionary relatedness, but it's not the goal of phylogeny to study genetic similarities.

[Paralith]

I don't want to be picky but... I agree with everything except that part; phylogeny is a description of genetic relatedness. Phylogeny is a description of evolutionary relatedness. Genetic relatedness is used as a mean to understand evolutionary relatedness, but it's not the goal of phylogeny to study genetic similarities.

 

That's a good point, and I'm glad you brought it up. I myself was taught that a phylogeny should be considered a hypothesis of evolutionary relationships, and that many sources should be sought to support that hypothesis, including genetic, anatomic, fossil, etc evidence. I think I focused on genetics because it was the most obvious contrast to the purely phenotypic scale that Mr.Skeptic was proposing, which I think is a much less accurate measure of actual evolutionary relatedness. It is not uncommon that close evolutionary relatives appear to differ radically in phenotype.

[Mr Skeptic]

I do not at all think that science should at any time make sacrifices simply so ignorant people won't get their panties in a knot. But that's just my opinion.

 

OK, so that is where we differ. I don't see it as making a sacrifice, just using an extra word ... kind of like some people would think nothing of "Gosh darn it all to heck" but would be offended if you said the actual meaning of that phrase.

 

Oh, and the public definitely needs to be aware of the renaming well before it happens. Otherwise they'll think we're being sneaky.

[Paralith]

OK, so that is where we differ. I don't see it as making a sacrifice, just using an extra word ... kind of like some people would think nothing of "Gosh darn it all to heck" but would be offended if you said the actual meaning of that phrase.

 

But it is a sacrifice. It's teaching a scientific inaccuracy to children for the sake of not hurting anyone's feelings.

 

Oh, and the public definitely needs to be aware of the renaming well before it happens. Otherwise they'll think we're being sneaky.

 

Once again: I don't see the worth in going to extra trouble to keep the ignorant calm and happy.

[PhDP]

I think I focused on genetics because it was the most obvious contrast to the purely phenotypic scale that Mr.Skeptic was proposing, which I think is a much less accurate measure of actual evolutionary relatedness. It is not uncommon that close evolutionary relatives appear to differ radically in phenotype.

 

True. It's fair to say that molecular systematics is more reliable than the old classifications based on morphology.

[CDarwin]

As for the OP, the ability to interbreed is not a good measure of relatedness. While there are less genetic differences between humans and chimps than there are between horses and zebras, one of those differences between humans and chimps has resulted in a chromosome change that highly reduces the chances of producing viable offspring between the two. Horses and zebras have many more differences, but none of those differences have resulted in a change of that nature.

 

Perhaps a good demonstration is the enormous variety of dog breeds. Terriers and great Danes are probably more divergent physically than humans and chimpanzees, yet they can fully interbreed and are indeed members of the same true species.

 

I'm sure some people will highly dislike it. But as I understand the current theory, classification should accurately represent phylogeny, and phylogeny is a description of genetic relatedness, not phenotypic similarity. Phylogenetically, it is completely accurate to place ourselves with the apes. To change the rule for humans just because some people don't like it and most people still like to think of humans as more different and special than other animals is simply bad scientific practice and not one that I think should be taught to students.

 

Then we'd have to chuck out the reptiles too. Lizards are more closely related to birds than they are to turtles.

 

Oh, and the public definitely needs to be aware of the renaming well before it happens. Otherwise they'll think we're being sneaky.

 

Who is 'we?' If scientists can't even agree on Homo/Australopithecus habilis I guarantee you Homo troglodytes is a long way off. Which is a sneaky way of pointing out a problem with putting humans and chimpanzees in the same genus. What do we do with all the fossil species that interceded between the last common ancestor and modern humans (and the ones between the common ancestor and chimpanzees too, presumably)?

[CharonY]

One general problem is that according to one of the basic tenets of the modern synthesis "The durable units of evolution are species...".

However, it is clear that on the prokaryotic level there are in fact no clear-cut species, except by drawing arbitrary lines. This however can clearly not be a fundamental unit of anything. Accordingly, declaring any lineage special does even make less sense. An additional problem is that genetic analyses do not give easy answers either. Especially HGT is a nasty thing to consider.

 

Finally I have to add that most current taxonomic studies place birds clearly in the class of reptilia.

[lucaspa]

I have heard it said that chimpanzees and humans are closer related to each other than horses and zebras, and to lions and tigers. If this is true, than why is it that the latter two pairs of creatures can interbreed, but humans and chimps can't?

 

Let's be clear. The biological species concept states that a species consists of a freely interbreeding population that produces fertile offspring.

 

Horses and zebras and lions and tigers do not freely interbreed. Yes, we can artificially inseminate the female of one of the pairs with the sperm of the other pair, but the product (such as a "liger") is not fertile.

 

Humans and chimps do not freely interbreed. We know that. Your question is: if we artificially inseminated a human woman with chimp sperm or a female chimp with human sperm, would we get a live baby?

 

There are ethical concerns why that is not done. You say you have heard of such being done. Do you have a source? There have been rumors that the Chinese conducted the experiment (human sperm to female chimp) but that is at the level of urban legend.

 

Perhaps a good demonstration is the enormous variety of dog breeds. Terriers and great Danes are probably more divergent physically than humans and chimpanzees, yet they can fully interbreed and are indeed members of the same true species.

 

That isn't certain anymore. It isn't certain that all the breeds of dogs still belong to one species. There are some crosses that you simply don't see. Reproductive isolation is more than just DNA sequences. There is genital incompatibility. Breeding a male Great Dane and female chihuaha will kill the chihuaha -- either during sex or during gestation.

 

You really need to do the interbreeding experiment with dogs to see if they really are a single species anymore. Genetically, they are 4 species.

 

Who is 'we?' If scientists can't even agree on Homo/Australopithecus habilis I guarantee you Homo troglodytes is a long way off. Which is a sneaky way of pointing out a problem with putting humans and chimpanzees in the same genus. What do we do with all the fossil species that interceded between the last common ancestor and modern humans (and the ones between the common ancestor and chimpanzees too, presumably)?

 

There are enough intermediate species in the hominid lineage to make it clear that chimps really do belong in a separate genus. The splitting and speciation since the last common ancestor has made 2 genera (at least). In fact, in the hominid lineage, there are at least 3 genera: Australopithecus, Paranthropus, and Homo. We don't know much about the chimp lineage since the last common ancestor, but I would be much surprised if the same situation did not apply there as well.

[CharonY]

That isn't certain anymore. It isn't certain that all the breeds of dogs still belong to one species. There are some crosses that you simply don't see. Reproductive isolation is more than just DNA sequences. There is genital incompatibility. Breeding a male Great Dane and female chihuaha will kill the chihuaha -- either during sex or during gestation.

 

You really need to do the interbreeding experiment with dogs to see if they really are a single species anymore. Genetically' date=' they are 4 species.[/quote']

 

But precisely this raises the question regarding the validity of such a kind of species concept. It is quite clear that isolation of gene pools (either due to genetic incompatibility, spatial isolation or morphological incompatibility) is not clear cut enough to warrant a classification on which further (more universal) theories can be based on. As I said before, species concepts of reproductive isolation do not work with prokaryotes (or for most non-sexually propagating organisms for that matter). Of course this is not directly related to the OP but is rather a general discussion on how species can be defined and whether such a distinction makes biological sense. The practical advantages are quite clear.