Descent of testicles.

This is only hypothesis. It is not eternal truth which have been discovered by two scientists in 1999. Their phylogeny tree do not conform others phylogeny trees of mammalian evolution. We don't have information about position of testicles of extinct mammalian orders and families. Authors themselves admit it, if you have read it more carefully:

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We suggest that the scrotum may have evolved before the origin of mammals, in concert with the evolution of endothermy in the mammalian...

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So they just suggest. They do not reveals any evidence it really happened. It is still open to discussion. It wouldn't be quite correct if we took it for granted at this time.

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There isn't a problem. The paper states that the scrota solution would be 'lost in mammal lineages as soon as an alternative solution' is found. The phylogeny shows that the lineage which includes elephants has indeed lost it. Why do you think there is a problem?

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The problem is also with the mentioned research. Scientists proposed three division of testicles. I would started with two - testicles inside body or testicles outside body. We can see that seals (Carnivora) or tapirs have testicles inside their bodies too. I cannot accept explanation that scrota solution would be "lost in mammal lineages as soon as an alternative solution". It has been solve so many times in different mammalian families - if they are correct - that one should really wonder why this didn't happened in all mammalian families.

Paul, I am afraid your latest post hasn't bring nothing new for ongoing discussion. As you know I am opponent of neoadarwinism and so your enumeration of neodarwinian approaches has left me unimpressed - it has no explanatory value for me as far as I can see that elephants, seals, bats, tapir etc... have testicles inside their bodies but other species and families don't.For me it means that all "cooling spermatozoa" explanation is ad hoc neodarwinian explanation with no scientific value. I admit that spermatozoa are sensible for higher temperature, but it can be acquired adaptation to "outdoor" condition and not the reason of descent of testicles. And obviously no such sensitivity exist amongst elephants anymore.

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Paul, I am afraid your latest post hasn't bring nothing new for ongoing discussion.

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It refutes your assertions. If you were already aware of and understood the refutations then that, I am afraid, is your problem.

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For me it means that all "cooling spermatozoa" explanation is ad hoc neodarwinian explanation with no scientific value

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Nobody has proposed such an explanation. The "cooling testicles" explanation that has been proposed, on the other hand, has sufficient evidence to make it plausible. We know that there ARE mammalian species that can suffer loss of male fertility if the testicles are warmed to core body temperature. There is no difficulty in suggesting that this was the general condition in early mammals.You may say that this is "not new" - because I have posted it before. However the reason for repeating it is that you have not rebutted it, or even truly acknowledged it.

OK, you are catching up. Yes, this is a hypothesis that is based on the evidence presented in the paper. Whose taking anything for granted? All I said was that "The most parsimonious explanation for the phylogeny is that descended testicles represents a primitive adaptation and their ascent represents a more recent adaptation."Do you disagree that it is the most parsimonious explanation? Please provide a better one if you have it. Yes, those are two divisions: scrotal and ascrotal. There is also descended and not descended. Ignoring this latter classification would surely render your topic absurd wouldn't it? You are being now-centric. The phylogeny seems to show an increase in the frequency of ascrotism over time. Whose to say that this pattern won't continue until all mammalian families are ascrotal?What would you expect from an inefficient search process that neodarwinism proposes? Would you expect that disparate lineages would simultaneously find a better solution?

I am afraid it refutes anything. Maybe for you claims like "having scrotum outside their bodies gives horses survival advantage" and "on the contrary having scrotum inside bodies gives elephants survival advantage" that this use of non-specified "survival advantage" explain something is only illusory for me. What sufficient evidence do you have on your mind?
Authors described their explanation as "untestable". Or using other words there is no evidence supporting it. Repeating doesn't made it more plausible. My argument is this - spermatozoa adapted to lower temperature outside body during descent of testicles. What evidence do you have that you dismiss my logic but you consider yours for the right one? I don't see also difficulty to see the same condition in early birds. Yet there were no descent of testicles. This argument seems to me to support my view.

I am not catching up. Maybe someone who is following our discussions would make wrong conclusions that problem has been solved by reading your post. I don't see there also any "evidence". The varycolored chart is not evidence it only presents observed facts. And this is really the point. The chart is misleading for our discussion. I claimed that "cooling spermatozoa" is no valid explanation for descent of testicles. You focused your attention to red linneages which represent only testicond organisation. But the problem are also grey ones. Obviously they are inside bodies so they are not cooled anymore and I suppose they have body temperature. Now imagine also those grey lineages as red and tell me if you see there any parsimonious explanation.

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You are being now-centric. The phylogeny seems to show an increase in the frequency of ascrotism over time. Whose to say that this pattern won't continue until all mammalian families are ascrotal?

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Ascrotal are also grey. I don't see there any increase or decrease of ascrotism over time. Random distribution I would say.

If you prefer you can reword my original phrase to reflect this. Change it to "Yes, this is a hypothesis that is based on the observed facts presented in the paper." I focussed on all of the data, and the patterning I observed. Can you give a more parsimonious explanation for the data in its totality? It's the same explanation. The most parsimonious explanation is that black represents the primitive condition and that grey represents a later type of adaptation. I see that grey universally comes out of black or white lines. Indicating that the black solution is probably ancestral to the grey solutions. What do you think the best explanation for the general pattern of black to grey to red is?It looks quite clear that the number of lineages which are grey increases as we go from bottom to top. I'm not sure how you are reading the chart that would give any other impression. Do you contend that there is a better way to colour the lines that makes it more parsimonious? Please, share your more parsimonious explanation.Edited by Modulous, : No reason given.Edited by Modulous, : No reason given.

You have written probably finally. I don't know in which points that chart represents other evolutionary charts of mammalian phylogeny. I haven't enough time for redrawing several charts and comparing them. Certainly I will do it if I am convince that the problem is worth of it. For me it is preliminary only a possible chart for phylogeny which is marked with families or orders with or without descent testicles.The possibility that testiles descended several times independently is not overruled by the chart. They ascended also several times independently according the chart. Yes it looks like that. But what you are doing is that you drives the discussion off topic. I didn't addressed the problem if descended testicles arose once or several times during evolution. I addressed the neodarwinian explanation of it and it is that descend testicles are device for cooling spermatozoa. The chart shows us that in cca 1/2 of cases testicles are in mammalian bodies. So obviously "cooling spermatozoa" is not such a difficult problem that shouldn't be overcome.We should take into consideration that adaptive radiation of mammalian orders was relatively fast process. Lineages must have been splitting from each other very fast. No mammalian orders arose last 40 million years, so every outlined orders has had enough time to get rid of scrotal testicles (if neodarwinian explanation is right). The evolutionary chart looks more like this:Page Not Found | We cannot find your page (404 Error) | Memorial University of Newfoundlandand there is no reason to look at distorted chart because the time scale is also important value at y-axis.
Edited by MartinV, : No reason given.

I thought you would understand that my insistence on 'most parsimonious' would imply that it was not gospel truth and that you understand the tentativity of science by now. Correct. The paper presents one piece of evidence for the hypothesis that one common ancestor with scrota had some kind of advantage, and the trait became common, but over time even better solutions were came upon.From this one paper alone, that is the most parsimonious explanation. Maybe other papers would give different conclusions.Still, I remain unconvinced that the pressure to develop scrota came about as a result of the cooling problem. I still think that the cooling problem came after the scrota, as a response to a different optimum operating temperature that the scrotum demanded.Once we have to come at least a basic agreement of the paper's contents you have presented I am happy to discuss some alternative hypotheses. And I pointed out that all the paper really says is that scrota are a primitive adaptation to a problem that better solutions came along to. The chart shows that it has taken millions upon millions of years for even a fraction of mammal lineages to solve the problem. Whether or not it is 'difficult' - it certainly doesn't seem to be trivial. I thought the neodarwinian explanation doesn't give an explicit time within which it has to have happened. Could you explain this?The evidence shows that 40 million years isn't enough time for all lineages to arrive at a solution.

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I am afraid it refutes anything. Maybe for you claims like "having scrotum outside their bodies gives horses survival advantage" and "on the contrary having scrotum inside bodies gives elephants survival advantage" that this use of non-specified "survival advantage" explain something is only illusory for me.

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Except I was quite specific about the advantages involved. Avoiding the decrease in fertility caused by warming the testicles is one. Losing the disadvantages of descended testicles - which you yourself refer to - was another. I never referred to a non-specified "survival advantage".It is antics like this that get you labelled a "troll". With some justification.

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What sufficient evidence do you have on your mind?

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The evidence in the blog post, and that referred to in my initial post of course.

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Authors described their explanation as "untestable". Or using other words there is no evidence supporting it.

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You are incorrect abut the meaning of "untestable". It does not mean that there is no evidence supporting it. What it means is that there is no way to set up a decisive test that would be likely to disprove it.

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Repeating doesn't made it more plausible.

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Nor does your comment make it any less plausible. You will have to deal with my evidence if you want to do that.

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My argument is this - spermatozoa adapted to lower temperature outside body during descent of testicles. What evidence do you have that you dismiss my logic but you consider yours for the right one?

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I consider the explanation I have offered plausible, not the definite truth. You dismiss my position for no given reason - not the opposite.In fact you have offered no logic so I certainly cannot dismiss it. But in fact I have provided evidence and explanations to support my view - and you have not. The fact that some species of mammal use alternative means of cooling their testicles would also seem to be a problem for your view.

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I don't see also difficulty to see the same condition in early birds. Yet there were no descent of testicles. This argument seems to me to support my view.

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Which only shows how poorly you grasp logic. Your argument does not support your view. Given the fact that there are alternative solutions there is no reason in neo-Dawinian theory to expect birds to end up with the same solution as mammals.

[Apologies for accidental edit (hitting "edit isntead of reply and not noticing) I have attempted to restore the original text so far as is possible. I invite Martin V to further correct these changes]There is an interesting post following doctor Myers article author of which claims that Werdelin and Nilsonne are wrong (see the post from Conrad Knauer) using outdated phylogeny tree. It means the authors are wrong with their supposisition of descended testicles of ancestral mammals. It would also means that descended testicles evolved exclusively in Boreoeutheria.comment 3726 by Conrad Knauer
Pharyngula - Hotell anbefalinger BarcelonaTHe authors of the original study used the wrong phyologenyThe author writes with capital letters this:EVERY SINGLE PLACENTAL MAMMAL WITH TESTICONDY IS IN AFROTHERIA.I have checked it and it seems to be true. And according the link he has given:They (afrotheria) appear to be the most primitive of the placental mammals.there was a split between Afrotheria and Boreoeutheria with the former mostly maintaining testicondy, while Boreoeutheria evolved exclusively descended testicles.see http://users.rcn.com/...yPages/V/Vertebrates.html#PlacentalsThis shows that elephants did not have ancestors with descended testicles and disproves the "cooling" hypothesisEdited by AdminPaul, : No reason given.Edited by AdminPaul, : [Correcting accidental edit so far as possible. Again, apologies]Edited by AdminPaul, : No reason given.

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Which only shows how poorly you grasp logic. Your argument does not support your view. Given the fact that there are alternative solutions there is no reason in neo-Dawinian theory to expect birds to end up with the same solution as mammals.

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Please see my previous post to Modulous. Your arguments and "evidences" are probably based on outdated cladogram.

Would you be shocked to learn that I agree? That isn't a supposition, it is their conclusion. You'd be on better grounds if you stated that their erroneous supposition is that the phylogeny tree is correct.As Conrad notes:

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What a difference a few years makes!

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And how! Isn't the advance of science great? Clearly the central hypothesis of Werdelin and Nilsonne was testable: since it failed!I had read the interesting (to this discussion) part of the wiki article on 'testicle' earlier and it says:

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The basal condition for mammals is to have internal testicles. Only the Boreoeutherian land mammals, the large group of mammals that includes humans, have externalized testicles. Indeed their testicles function best at temperatures lower than their core body temperature. Their testes are located outside of the body, suspended by the spermatic cord within the scrotum. The testes of the non-boreotherian mammals such as the monotremes, armadillos, sloths, elephants remain within the abdomen.[3] There are also some Boreoeutherian mammals with internal testes, such as the rhinoceros.

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It then goes on to give the hypotheses about why we have scrota:

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More efficient. The classic hypothesis is that cooler temperature of the testes allows for more efficient fertile spermatogenesis...However, the question remains why birds despite having very high core body temperatures have internal testes and did not evolve external testes.[4] It was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes are able to function at core body temperature.[4]

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2) Irreversible adaptation to sperm competition. It has been suggested that the ancestor of the boreoeutherian mammals was a small mammal that required very large testes (perhaps rather like those of a hamster) for sperm competition and thus had to place its testes outside the body.[5] This led to enzymes involved in spermatogenesis, spermatogenic DNA polymerase beta and recombinase activities evolving a unique temperature optimum, slightly less than core body temperature. When the boreoeutherian mammals then diversified into forms that were larger and/or did not require intense sperm competition they were stuck with enzymes that operated best at cooler temperatures and had to keep their testicles outside the body.

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3) Protection from abdominal cavity pressure changes. One argument for the evolution of external testes is that it protects the testes from abdominal cavity pressure changes caused by jumping and galloping.[6]

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As I stated in a previous post, I don't think the cooling hypothesis is the best one. I prefer the second hypothesis, irreversible adaptation to sperm competition.

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--------------------------------------------------------------------------------The author writes with capital letters this:
EVERY SINGLE PLACENTAL MAMMAL WITH TESTICONDY IS IN AFROTHERIA.I have checked it and it seems to be true. And according the link he has given:They (afrotheria) appear to be the most primitive of the placental mammals.--------------------------------------------------------------------------------Here is where your logic fails you. That evidence only indicates that the Afrotheria had a common ancestor with testicondy. It does not tell us whether that common ancestor appeared before or after the split between Afrotheria and the remaining placental mammals. ("Most primitive" only means that the other placentals share derived traits not found in Afrotheria, indicating that that division was the first of significance to be found in the placentals).The correct way to resolve it is to repeat the analysis with a more accurate phylogenetic tree. And I note that you miss a far more significant piece of evidence - that testicondy is also found in monotremata. That is in the phylogenetic diagram and in Knauer's comments.

Obviously it is your custom to declare my logic as wrong. But I would reccomend you to have a look on some up to date phylogenetic tree. You would see that Monotremata, Marsupalia and Afrotheria makes a
part of tree where testicondy is most parsimonious solution. These are facts. And what's your point using strictly and correct logic?