When Did Male and Female Humans Fully Distinguish in Evolution?

[pgardn]

yes, nipples are peculiar to mammals, AFAIK. also, i think it's important to remember that we males also have both X and Y copies of genetic code. we are essentially both male and female. and our maleness is simply an expression of that Y-ness (perhaps some suppression of X-ness?). indeed, males can, and do lactate, given enough of the proper hormones like prolactin. and with diseases like androgen insensitivity syndrome, we males can look pretty indistinguishable from females.

And females and males basically in early developmental stages are much the same which is of course explained by the above. If you "guys" really want to experience something interesting you should read about male reproductive parts and female reproductive parts and see how much they have in common even though the outcome in development from a purely physical view may make them seem drastically different.

 

[Jon Richfield]

... males didn't develop nipples that serve no function. Our nipples (biologically) serve the same function that they do for women.

Ahem... it isn't as simple as that. It is perfectly possible in principle for adaptation to produce either functioning, but non-functional (completely or nearly completely), or totally non-functioning organs in different castes or genders. Human nipples are a case in point. Some of us have been talking about human male lactation for example, but it is not always possible, even if the necessary hormones are supplied artificially. I don't have figures, but many or most males don't have the necessary physical ducts in the nipples by the time of puberty.
Also, I don't reckon that it counts as biological adaptation if it depends on "artificial" manipulation that does not occur "in a state of nature" as a result of adaptive selection. (I refuse to go into the question of where "natural" selection ends and "artificial" manipulation begins!)
You see, what matters is the inclusive burden of selection. As someone mentioned, the nipples are the product of an embryogenic process that begins similarly in both genders. To avoid that happening would require a huge selective burden, whereas a few abortive nipples are usually too trivial to reckon in. Notice that in some ways the adaptation in females is far more specialised than in males, because they must get it right. In us males, our non-functioning vestiges require no more adaptation than keeping out of the way. Now, our primitive nipple count is more like six than two, but it is unusual to see signs of more than two in women, where we breastless men commonly have supernumerary nipples, only the extra ones are so small that we usually don't notice them. I had been adult for years when I happened to notice that an old friend had six, of which the lower four were basically pigmented dots. I then inspected myself and found that I had two extra, about at the level of my lower ribs. I had always thought that they were freckles! Since ours don't generally develop further, it is not important to control their appearance, but for women it is important, so the controls are not often so lax. But not that those extra "nipples" really, really are not as a rule functional at all. They are essentially areolar freckles.

In short, I agree with Pgardn about the unity of male and female ontogeny.

In other words, isn't it completely possible that sexual differentiation happened first (say in reptiles or therapsids) and nipples came later (with mammals) and was applied indiscriminately to both sexes; and that eventually, through socially driven epigenetics, male and female nipples took on different shapes? Or maybe even because the tribes who's males were out hunting instead of lactating survived, for instance?

Certainly, more or less, but we are discussing way back. Tribes don't come into it. Lactation is part of a generic process of physiological secretion for feeding offspring, and in mammals at least, it started before our ancestors looked like tree shrews, let alone monkeys. We don't know just when the first true mammalian lactation began, but it might well have started with the development of hair and sweat glands, probably before the upper Jurassic if you ask me.
It was in many ways not a very striking development really. Some birds, some fish, and some insects, to grab a few examples just off the cuff, produce secretions for the feeding of their young. The said secretions are pretty well universally derived from other secretions that some ancestral baby began to lick up or swallow, or even bite off, along with the parental mucus when the parent fed it. To this day monotremes don't have proper nipples, just multiple little ducts opening into external hair tufts for the young to lick.
Fish such as tilapia and discus feed their fry on mucus, either inside the mouth, or a specially thick secretion around the lips and gill coverts. Pigeons' "milk" is from mucus glands in the throat. Get the picture? It is a coherent one, I think you will agree.

I'm just trying to understand what would be improbable about the way I'm envisioning it.

So? I, for one, am no physicist. If I'm not shy about asking for help with physics, or even arguing about it, I don't see why you should be shy about discussing biology. Your general line of thought was quite reasonable, and apart from a bit of cross-purposes, I don't think anyone thought anything else. Or begrudged you your thinking. It all is science anyway, no matter what Rutherford thought in his ignorance.

Go well, and enjoy.

Jon

 

[pgardn]

You are right of course, that we have a perennial dilemma in conveying technical subjects (not necessarily biological). Ideally we should begin with the fundamental concepts and build from there, bottom up. In practice, that often does not work when dealing with people who are not going to deal with the subject at some depth. Then top-down is commonly the best, in fact the only approach. Actually, even for specialist students who are going to take the subject to advanced levels, one usually needs a mix of bottom-up and top down. To do it one way only takes, not just a brilliant teacher, but an inspired one with brilliant and motivated students!
Sorry, slight digression that was! What I had been aiming for was to convey a basic concept in the light of which the original question would appear in a slightly simpler perspective. Unfortunately, my experience is that if you simplify a matter in a way that your audience does not understand, they will think that you had complicated it...
Well, I feel another wave of simplification coming over me; wish me luck!

Jon

Which is why evolution on the whole can actually be very difficult to understand in its overwhelming richness. It requires a lot of background reading and critical thinking. One has to both understand the unity among all living things and throw in a dash of the complexity of the amazing array of diversity and how it might have come about from a historical biological perspective. I think the subject takes a long time to appreciate fully. A lot of reading...

I found that Steven J. Gould first, and then Ernst Mayr after, helped me quite a bit. A smidgen of Richard Dawkins for entertainment along the way. Lots of others but I found these fellows to be quite good with Mayr being very technical. The Growth of Biological Thought was very good but needs updating will all the "recent" advances in molecular biology.

 

[Jon Richfield]

Which is why evolution on the whole can actually be very difficult to understand in its overwhelming richness. It requires a lot of background reading and critical thinking. One has to both understand the unity among all living things and throw in a dash of the complexity of the amazing array of diversity and how it might have come about from a historical biological perspective. I think the subject takes a long time to appreciate fully. A lot of reading...

I found that Steven J. Gould first, and then Ernst Mayr after, helped me quite a bit. A smidgen of Richard Dawkins for entertainment along the way. Lots of others but I found these fellows to be quite good with Mayr being very technical. The Growth of Biological Thought was very good but needs updating will all the "recent" advances in molecular biology.

Quite right. I am fond of pointing out that there are certain subjects that are intellectual tarpits. They are treacherous because the basic concepts are simple, so people think that they understand the subject because they understand those ideas. But the way those concepts combine can be very complex indeed. Two examples are probability theory and evolution. Dead simple basic concepts, but heaven help anyone who gets too arrogant!
One mark of someone mature in such a field is that he is no longer embarrassed when he makes a mistake, but is very careful about committing to any hard and fast opinions; that kind of sucker bait is for the tyros.


Jon

 

[jackson6612]

Suppose a biological life started in a furnace. When a first living organism developed, it went on to change into more advanced forms of life and ultimately branching out into several different varieties of life - animals , birds, etc. Is that furnace still there? I assume that furnace had to be earth. I mean to say is there some kind of organism still on its way to become a human in future? Dinosaurs were also the result of evolution. If that furnace is still working, then there could be dinosaurs again in the future, perhaps. I hope you would be able to understand what I'm trying to say. Thanks for reading this.

 

[jackson6612]

I think that that furnace has ceased working because conditions on Earth have changed and are not favorable anymore for its working.

 

[AlexB2010]

I think that that furnace has ceased working because conditions on Earth have changed and are not favorable anymore for its working.

The "furnace" is still working, the selection environment changed.

Alex

 

[Pythagorean]

Ahem... it isn't as simple as that. It is perfectly possible in principle for adaptation to produce either functioning, but non-functional (completely or nearly completely), or totally non-functioning organs in different castes or genders. Human nipples are a case in point. Some of us have been talking about human male lactation for example, but it is not always possible, even if the necessary hormones are supplied artificially. I don't have figures, but many or most males don't have the necessary physical ducts in the nipples by the time of puberty.
Also, I don't reckon that it counts as biological adaptation if it depends on "artificial" manipulation that does not occur "in a state of nature" as a result of adaptive selection. (I refuse to go into the question of where "natural" selection ends and "artificial" manipulation begins!)
You see, what matters is the inclusive burden of selection. As someone mentioned, the nipples are the product of an embryogenic process that begins similarly in both genders. To avoid that happening would require a huge selective burden, whereas a few abortive nipples are usually too trivial to reckon in. Notice that in some ways the adaptation in females is far more specialised than in males, because they must get it right. In us males, our non-functioning vestiges require no more adaptation than keeping out of the way. Now, our primitive nipple count is more like six than two, but it is unusual to see signs of more than two in women, where we breastless men commonly have supernumerary nipples, only the extra ones are so small that we usually don't notice them. I had been adult for years when I happened to notice that an old friend had six, of which the lower four were basically pigmented dots. I then inspected myself and found that I had two extra, about at the level of my lower ribs. I had always thought that they were freckles! Since ours don't generally develop further, it is not important to control their appearance, but for women it is important, so the controls are not often so lax. But not that those extra "nipples" really, really are not as a rule functional at all. They are essentially areolar freckles.

In short, I agree with Pgardn about the unity of male and female ontogeny.


Certainly, more or less, but we are discussing way back. Tribes don't come into it. Lactation is part of a generic process of physiological secretion for feeding offspring, and in mammals at least, it started before our ancestors looked like tree shrews, let alone monkeys. We don't know just when the first true mammalian lactation began, but it might well have started with the development of hair and sweat glands, probably before the upper Jurassic if you ask me.
It was in many ways not a very striking development really. Some birds, some fish, and some insects, to grab a few examples just off the cuff, produce secretions for the feeding of their young. The said secretions are pretty well universally derived from other secretions that some ancestral baby began to lick up or swallow, or even bite off, along with the parental mucus when the parent fed it. To this day monotremes don't have proper nipples, just multiple little ducts opening into external hair tufts for the young to lick.
Fish such as tilapia and discus feed their fry on mucus, either inside the mouth, or a specially thick secretion around the lips and gill coverts. Pigeons' "milk" is from mucus glands in the throat. Get the picture? It is a coherent one, I think you will agree.



So? I, for one, am no physicist. If I'm not shy about asking for help with physics, or even arguing about it, I don't see why you should be shy about discussing biology. Your general line of thought was quite reasonable, and apart from a bit of cross-purposes, I don't think anyone thought anything else. Or begrudged you your thinking. It all is science anyway, no matter what Rutherford thought in his ignorance.

Go well, and enjoy.

Jon

Well, thank you for a thorough reply!

I guess I had been under the impression that there was no hormone therapy necessary, and that if we played with our nipples consistently enough, we would begin to develop mammary glands.

Well, bummer, I guess I don't have an excuse anymore...

 

[nismaratwork]

Well, thank you for a thorough reply!

I guess I had been under the impression that there was no hormone therapy necessary, and that if we played with our nipples consistently enough, we would begin to develop mammary glands.

Well, bummer, I guess I don't have an excuse anymore...

On the bright side, think of how you'll avoid the need to wear little band-aids over them to avoid chafing!

 

[Jon Richfield]

Suppose a biological life started in a furnace. When a first living organism developed, it went on to change into more advanced forms of life and ultimately branching out into several different varieties of life - animals , birds, etc. Is that furnace still there? I assume that furnace had to be earth. I mean to say is there some kind of organism still on its way to become a human in future? Dinosaurs were also the result of evolution. If that furnace is still working, then there could be dinosaurs again in the future, perhaps. I hope you would be able to understand what I'm trying to say. Thanks for reading this.

Jackson,

as I read your question, it is not clear to me whether you are referring to the nature of the environment as the "furnace" that supplies the power and material for the development of life, or whether you are referring to the mechanism and process of biological evolution in a more abstract line of thought.

Either would be reasonable in context.

So, firstly the nature of the environment and the populations in which adaptation occurred (and occurs) has changed repeatedly in the last few billion years on this planet. Some quite subtle changes have led to huge consequences in the history of our biology. My own bet is that we neither know of, nor understand one in 10 of the major changes of this type. And I say that in full appreciation of some very ingenious work and remarkable revelations.

Personally my attitude towards palaeontology is one of fascinated grief. It is a stressful subject to me. I just cannot stand the idea of all those marvellous creatures that I shall never see alive, nor understand the biology of. And yet there are excellent (if speculative) arguments for why some very impressive organisms died out. Sometimes it was because of changing conditions. For example some of the giant arthropods of the Carboniferous period might not have been viable in the lower oxygen levels that have reigned since then. Maybe we have no giant dragonflies or millipedes, simply because they could not breathe our air. Maybe seed plants took over simply because they did not need liquid water for their pollination.

Some people have made a great fuss about the explosion of new phyla in the Cambrian period, but actually it might be a better way of looking at it, to see the period as a loss of phyla. Late Precambrian life, such as the organisms that left the fossils of the Burgess shale and the Ediacaran fossils seem to have been wildly varied. By the end of the Cambrian we were left with a few dozen phyla.

These remarks are not so much a simple as simplistic, misleadingly so. All the way from the first development of cells, to actual modern times, we have developed into narrower and narrower basic plans of construction, what the comparative morphologist would call a bauplan. Every now and then a new bauplan, such as the arthropods all molluscs would take over and eliminate whole classes of rivals. Sometimes the bauplan that took over would be extremely unobvious, for instance the early chordates were not at all very promising. However once bony fish became dominant in the ocean, many other lines simply vanished. With each such an advance there would be dramatic radiation into wide varieties of lines of specialisation, but the number of bauplanne tended to reduce. For example, varied though they be, our modern birds are a rather thin sample of the fellow dinosaurs that they survived.

Such tendencies are not universal of course, we still have microbes apparently nearly identical to the dominant forms of two or 3 billion years ago, and worms very similar to those of five or 6 hundred million years ago and so on.

It is a large subject.

The second possibility was that the question you had in mind concerned the process of evolution as such. If that is what you meant, yes, it is still going strong and in principle it is hard to see how it could stop as long as anything like a living ecology based on reproduction with variation existed. It is a principle only arguably less fundamental than say, thermodynamics. In fact the two are very closely related, because like thermodynamics, Darwinistic evolution can be seen as a consequence of information theory.

Does that help?

Jon

 

[jackson6612]

Does that help?

Jon, it would be a lie to say I completely understood it. But I genuinely admire and respect people like you who so much sincerely strive to help others without any monetary incentive. I offer you and others my thanks and best wishes.

 

[Jon Richfield]

Jon, it would be a lie to say I completely understood it. But I genuinely admire and respect people like you who so much sincerely strive to help others without any monetary incentive. I offer you and others my thanks and best wishes.

Only a pleasure, but I wish I could put it more clearly and usefully to the enquirer. If you can at any time identify paragraphs and themes that gave you problems, please feel welcome to ask again accordingly,

Cheers,

Jon

 

[Ken Natton]

My problem is that I come to this thread very late in the conversation, and my contribution may not seem terribly relevant to the active discussion. But I have a perspective to offer on the theme of the thread, one that offers some possible indicators rather than absolute answers to some of the questions jackson6612 asked right at the head of this thread. And one that enables me to offer an informed, but nonetheless partly speculative answer to a question that has recurred at different points throughout the thread – why do men have nipples?

Within the last day, I have posted a reply on another similar thread about my understanding of just how early in the evolutionary chain sexual reproduction developed. Along with that understanding, I have cited the text from which I took that understanding, so people are free to challenge my interpretation of the text or to challenge the text itself. The understanding that I am about to offer here is also not just something I have thought up myself. It comes from something I read, written by someone who seemed to know what he was talking about. It will be much more difficult, but not necessarily impossible for me to recover the precise reference. It was actually a medical textbook that I took this understanding from. I am not, and have never been a medical student. I did not read the whole book, just, in fact this one passage, and I read it in an idle moment. But I found it fascinating and it did seem to make a great deal of sense in explaining much about what is actually the difference between male and female, to which I would offer this taster – a great deal less than you might think.

In any case, enough of the justifications, here’s the point. Though it is clear that the ‘y’ chromosome is present in male embryos and absent in female embryos right from conception, it is not the case that male embryos develop as males and female embryos develop as females right from the start. Neither is it the case that the initial stages of embryonic development are essentially androgynous and the separation into female or male occurs later in the development. The key is that all embryos begin to develop as females, and would develop all the way to maturity as females but for the intervention, where present, of the ‘y’ chromosome. Human embryonic development takes about eight weeks. I cannot honestly remember the exact point in the course of that development that this text identified as the point where the ‘y’ chromosome begins to exert its influence, but I do remember that it is astonishingly late.

So jackson6612’s speculation ‘which would mean male hadn’t become full male yet’ was prescient. He was just looking in the wrong direction. Don’t look for the answer back down the evolutionary development chain. Look for it back down the embryonic developmental sequence. Although, drifting away from the point a little, there are cases where our modern embryonic development does replay little bits of our evolutionary history.

In any case, my guess at the answer to the question, why do men have nipples? Because they develop before the ‘y’ chromosome does its thing. Mammary glands are, after all, the very thing that define us as mammals.

 

[Jon Richfield]

That sounds about right to me. Ugly little things aren't they? :p

Since you ask, no they are not. No more so than say, humans, hummingbirds, orchids, octopus, redwoods, spiders, or medfly.

And incidentally, no, sex did not start with the chordate descendants of sea squirts. It is far older than that. The discussion in this thread is very frustrating because it begins with misconceptions several steps removed from the fundamentals of sex and its many implications in evolution. I reckon that some of the most confused participants need to go back to basics and do a LOT of reading and thinking.

In case anyone reads this and thinks that I am being either patronising or derogatory, forget it. The plain fact of the matter is that it is about as easy to make sense of such matters without developing a perspective of the basics, as to understand quantum theory without mastering bra-ket maths.

Sorry, naught for your comfort. Have as much fun as you like, but, until you have done your homework, don't delude anyone, including yourself, that you have any coherent question, or any coherent understanding of what it would take to recognise the incoherence.

 

[Jon Richfield]

In any case, my guess at the answer to the question, why do men have nipples? Because they develop before the ‘y’ chromosome does its thing. Mammary glands are, after all, the very thing that define us as mammals.

Sorry Ken, I don't buy this. Most of what you wrote had merit, but no, except in a trivial, largely etymological, sense, no, they are not, not any more than say our nitrogenous excretion biochemistry. The fact that it is adequate to argue that if one finds a mammary gland one knows that a mammal was involved somewhere, does not imply that it is definitive. The same could be said of hair (distinct from say chetae or filoplumes, right?) or sweat glands, or enucleated erythrocytes, no?

Cheers,

Jon

 

[nismaratwork]

Since you ask, no they are not. No more so than say, humans, hummingbirds, orchids, octopus, redwoods, spiders, or medfly.

And incidentally, no, sex did not start with the chordate descendants of sea squirts. It is far older than that. The discussion in this thread is very frustrating because it begins with misconceptions several steps removed from the fundamentals of sex and its many implications in evolution. I reckon that some of the most confused participants need to go back to basics and do a LOT of reading and thinking.

In case anyone reads this and thinks that I am being either patronising or derogatory, forget it. The plain fact of the matter is that it is about as easy to make sense of such matters without developing a perspective of the basics, as to understand quantum theory without mastering bra-ket maths.

Sorry, naught for your comfort. Have as much fun as you like, but, until you have done your homework, don't delude anyone, including yourself, that you have any coherent question, or any coherent understanding of what it would take to recognise the incoherence.

Beyond your diatribe, would you care to offer an actual contribution as to when this divergence developed?

 

[Jon Richfield]

Beyond your diatribe, would you care to offer an actual contribution as to when this divergence developed?

Way back. Very possibly as a side effect of the nature of the first mitotic divisions that cells systematically achieved in the first few hundred million years of life on the planet. And as for gender, probably well within two billion years of that time. We can distinguish gender nowadays even in certain fungi and algae. Various classes of gender in fact; it is a very general concept and seems to have been developed in many ways independently in various biological kingdoms, including several times independently within single kingdoms.

Does that give you any clues? Pretty elementary biology, I should have thought. If you would like anything more specific, please suggest some of the points to cover; I do not have the time at the moment for a detailed work on the subject (or range of subjects actually.)

And incidentally, what is this ugliness thing of yours? Or shouldn't I ask?

 

[Jon Richfield]

In any case, enough of the justifications, here’s the point. Though it is clear that the ‘y’ chromosome is present in male embryos and absent in female embryos right from conception, it is not the case that male embryos develop as males and female embryos develop as females right from the start. Neither is it the case that the initial stages of embryonic development are essentially androgynous and the separation into female or male occurs later in the development. The key is that all embryos begin to develop as females, and would develop all the way to maturity as females but for the intervention, where present, of the ‘y’ chromosome. Human embryonic development takes about eight weeks. I cannot honestly remember the exact point in the course of that development that this text identified as the point where the ‘y’ chromosome begins to exert its influence, but I do remember that it is astonishingly late.

Ken, apart from some remarks I have made in other postings, some in answer to you, I would like you to consider the fact that gender determination is not a function of "Y-chromosomes" specifically. Nor are all Y-chromosomes homologous in this sense. We certainly have had well-defined gender, not only in chordates, from well before there were anything like modern Y-chromosomes. And even in modern chordates (Craniates in fact) Y-chromosomes are not either necessary at all, nor do they have the same effects. In birds, insofar as they are homologous, which is not so far (they are not in all way truly analogous even!) the Y-chromosome determines the female gender! And in many reptiles, not necessarily closely related, such as chelonians and crocodilians, gender is temperature-determined during incubation.

So certainly much of what you say is true about the way in which mammalian development of (especially male) gender occurs, and how it affects the interesting, but to my mind rather minor, issue of male nipples, but at a slightly deeper and correspondingly more general and more interesting (to my taste) level, if one is looking for more generally meaningful, insight-giving views of gender, one really does have to go far, far back into our past. The male nipple is pretty trivial in such a perspective.

Go well,

Jon

 

[nismaratwork]

Way back. Very possibly as a side effect of the nature of the first mitotic divisions that cells systematically achieved in the first few hundred million years of life on the planet. And as for gender, probably well within two billion years of that time. We can distinguish gender nowadays even in certain fungi and algae. Various classes of gender in fact; it is a very general concept and seems to have been developed in many ways independently in various biological kingdoms, including several times independently within single kingdoms.

Does that give you any clues? Pretty elementary biology, I should have thought. If you would like anything more specific, please suggest some of the points to cover; I do not have the time at the moment for a detailed work on the subject (or range of subjects actually.)

And incidentally, what is this ugliness thing of yours? Or shouldn't I ask?

If it's so elementary, I'm sure you'll have no problem providing sources which confirm your statements; I look forward to seeing them. As for the ugly comment, it was a joke. You need to relax in the worst way. You've provided your view of when sexual division began, now you get to back it up with something solid, and if not, go home.

 

[Ken Natton]

Hi Jon,

For certain, I agree with you that the male nipple thing is trivial, I only raised it because it has been a subject of discussion on this thread, and it does seem to be one that a lot of people latch on to as a mystery of evolution.

I’m surprised that you reject the idea of mammary glands as a defining mammalian feature. Apart from the obvious etymological connection, is not suckling the young the key defining feature of a mammal?

And, connected with another one of my very favourite stories from the annals of human evolution, my understanding was that sweat glands, or at least a profusion of sweat glands, was very much a specifically human feature. The story, as I heard it, is closely connected with the reason why we became the naked ape. It’s all about our big, energy hungry, heat producing brains.

 

[jackson6612]

Ken, your help and contribution is greatly appreciated. Thank you.

But I found it fascinating and it did seem to make a great deal of sense in explaining much about what is actually the difference between male and female, to which I would offer this taster – a great deal less than you might think.

I'm also an English learner and have a terribly bad habit of pestering others to explain their statements. Sorry, I couldn't understand the bold part. I have checked 'taster' in M-W.

 

[Ken Natton]

Hi jackson6612,

‘Taster’ in that context, is an idiom. Taste is one of our senses, the one we use to detect the flavour of our food and drink. So originally, a taster was a little free sample of some food or drink, designed to entice you into spending your money on buying the full portion. Subsequently, more idiomatically, it has become a small snippet of anything we might consume – like a film or a popular song – designed to entice us into consuming the full version.

So I suppose that I was imagining that people reading my post might be enticed into being interested in my main point by the snippet of information that men and women are less different than you might think.

 

[Jon Richfield]

If it's so elementary, I'm sure you'll have no problem providing sources which confirm your statements; I look forward to seeing them.

Sources? Sources? Are you serious? Sources for what? Suppose you specify a few of the points that you find implausible and explain what you find difficulty with. I don't ask you to prove anything, just explain what you see as errors of fact or logic. (Facts, you know? Like the evolutionary level at which we find the most elementary examples of sexual (read genetic in this context) recombination, and in comparison the levels at which we find the most elementary examples of distinct gender? Or the levels of stromatolites at which we first find evidence for multicellular life? These connections are not too complicated for you I hope? And logic, you know? Like the connection between organisational level and derivation of evidence for phylogeny? And the connection between phylogenic history and adaptive selective pressures? Non-biologists often come up with some peculiar lines of discussion, but this one is a lulu.)
Sources for the likes of what I mentioned would include most of the introductory university texts I have seen so far for botany, cytology, or microbiology. You know? Or if those are too challenging, try Ken's
example: JMS & ES. Available from Amazon, most technical bookshops, and practically all university libraries (assuming they have biology faculties of course!) And those are excellently written by leading authorities (unless you happen to know better of course!) I suppose if I remarked on the catalytic effect of soluble iron salts on the corrosion of copper in the presence of air and water, you would ask for sources?
Well man, I really must admit you had me going there for a minute!

As for the ugly comment, it was a joke. You need to relax in the worst way. You've provided your view of when sexual division began, now you get to back it up with something solid, and if not, go home.

Oh, so you admit that they are real pretty huh? That's better. You got any sources? A joke hm? Did anyone laugh but you? Or grin?

Now, let's hear your sources for the origins of "sexual division" post chordate. I won't ask you to limit yourself to first-year references; post-graduate will do just fine, so just don't say I never do you any favours!

 

[Jon Richfield]

For certain, I agree with you that the male nipple thing is trivial, I only raised it because it has been a subject of discussion on this thread, and it does seem to be one that a lot of people latch on to as a mystery of evolution.

Ken, I am sorry if I gave you the impression that I thought that the nipple thing is in itself trivial. It is not. I just meant that in the perspective of the very large and fundamentally important subject you raised, it is just one small example of secondary sexual characteristic and of recent origin compared to primary mammalian sexual characters. I don't, by way of analogy, regard you personally as trivial, but I doubt that you would feel deeply offended if I overlooked you in juxtaposition with say, Grand Canyon... ;-)

You are right that many people do latch on to it as a mystery of evolution, but as I see it, they miss a lot of points dramatically. Your own discussion raised typical examples of such points very pertinently and correctly. Remember your discussion of intrauterine development and the point at which the secondary (and some primary) male sexual characteristics began to develop? You can carry this further; other secondary (and primary) characteristics don't complete their development till the end of puberty at least, some even later.

I’m surprised that you reject the idea of mammary glands as a defining mammalian feature. Apart from the obvious etymological connection, is not suckling the young the key defining feature of a mammal?

Please do not confuse "the idea of mammary glands as a defining mammalian feature" with "the idea of mammary glands as the defining mammalian feature". You did say: "Mammary glands are, after all, the very thing that define us as mammals," right? (My italics of course.) Let me give you an analogy to illustrate: a biologist for whose work I had respect for shocked me by insisting that the hook-lip of the black African rhino was "the most important" difference between the black and white rhinos. Biologically the statement was meaningless at best. What he really seems to have meant was that it was the most obvious (he was no mammalogist!). Actually there are no end of differences, and many of them are functionally more important, such as the differences in teeth and digestive systems (the two species have different diets.)
Now, I was not disputing that you could easily tell them apart by their upper lips, just that the lips, though sufficient as a diagnostic feature, were not necessary. Any mammalogist looking at a picture of an African rhino with the lip not visible could tell the species apart. (So could any layman familiar with the animals.) And the rhinos didn't develop their lips for the convenience of taxonomists; they have more important functions that represent adaptations to the animals' lives. Right?
Now, certainly, as I said, given the appropriate part of a mammal's anatomy, a mammalogist could identify the mammae, and tell you that they did not come from a bird. No argument. But would you like to sit down for a while and list major features of a mammal's anatomy that would not do just as well? How about the skin? Hair? Teeth? Eyes? Feet? External ears? Erythrocytes? Brain? Genitals? Adipose organ? Kidneys?

Don't let me rush you.

And don't let me leave you thinking that I would exclude nipples from the list; I simply say that they are just one example among many. And what is more, if I gave you the nipples of a monotreme to identify, you might have a merry dance before you succeed!

And, connected with another one of my very favourite stories from the annals of human evolution, my understanding was that sweat glands, or at least a profusion of sweat glands, was very much a specifically human feature.

We all have our favourites, even I, and we all get led astray by them, even I. (NO? Oh yes! Really!) The profusion of sweat glands is by no means specifically human, and if it were, that would hardly be relevant. As things stand, there are several kinds of sweat glands, and most mammals have one or more. (I have seen claims that cetaceans lack them completely, but I have also seen it denied. It is hard to prove a negative.) The point is that finding even one undeniable sweat gland of any mammalian type is sufficient to tell you that you are not working with a fish or fowl.
Apes have plenty, though we are the sweatiest apes, I believe. Horses have more than we have.

The story, as I heard it, is closely connected with the reason why we became the naked ape. It’s all about our big, energy hungry, heat producing brains.

That story may have merit, but as it stands it is a classic example of a "Just-So" story. As a hypothesis it is not wildly unreasonable, but as commonly retailed, it is a bit holey. One of the holes is that the brain's heat production has been widely exaggerated. Another is that the range of heat shedding techniques among animals is quite wide enough to deal with the extra bit of cranial heat that we produce. And just in case you had not noticed, most of that mammary evidence for our mammalian nature, the more attractive, the more so, gets hidden from us behind... Artificial means of reducing heat loss!

I repeat: the whole theory (though personally I don't like it) is not to be rejected wholesale out of hand, but there is a heck of a lot ground to cover before it can be regarded as established.

Am I making the right points? Feel welcome to holler!

Cheers,

Jon

 

[nismaratwork]

Sources? Sources? Are you serious? Sources for what? Suppose you specify a few of the points that you find implausible and explain what you find difficulty with. I don't ask you to prove anything, just explain what you see as errors of fact or logic. (Facts, you know? Like the evolutionary level at which we find the most elementary examples of sexual (read genetic in this context) recombination, and in comparison the levels at which we find the most elementary examples of distinct gender? Or the levels of stromatolites at which we first find evidence for multicellular life? These connections are not too complicated for you I hope? And logic, you know? Like the connection between organisational level and derivation of evidence for phylogeny? And the connection between phylogenic history and adaptive selective pressures? Non-biologists often come up with some peculiar lines of discussion, but this one is a lulu.)
Sources for the likes of what I mentioned would include most of the introductory university texts I have seen so far for botany, cytology, or microbiology. You know? Or if those are too challenging, try Ken's
example: JMS & ES. Available from Amazon, most technical bookshops, and practically all university libraries (assuming they have biology faculties of course!) And those are excellently written by leading authorities (unless you happen to know better of course!) I suppose if I remarked on the catalytic effect of soluble iron salts on the corrosion of copper in the presence of air and water, you would ask for sources?
Well man, I really must admit you had me going there for a minute!



Oh, so you admit that they are real pretty huh? That's better. You got any sources? A joke hm? Did anyone laugh but you? Or grin?

Now, let's hear your sources for the origins of "sexual division" post chordate. I won't ask you to limit yourself to first-year references; post-graduate will do just fine, so just don't say I never do you any favours!

The error that I think you've made is condemning one opinion in favor of your own, when you have no more ability to back that opinion than anyone else. Until you do, I'm not wasting my time with this. The title of the thread specifically referred to male and female differentiation, not simply the emergence of sexual reproduction. You're entitled to your opinions, but present them as such unless you're willing and able to back them up immediately.

 

[Jon Richfield]

The error that I think you've made is condemning one opinion in favor of your own, when you have no more ability to back that opinion than anyone else. Until you do, I'm not wasting my time with this. The title of the thread specifically referred to male and female differentiation, not simply the emergence of sexual reproduction.

Well NAW, you have a nice line in emotive nomenclature. When you present an opinion I assume you call it debate or something equally urbane. When anyone disagrees and points out holes in your assumptions or reasoning, that is condemnation. Yes?
Well, if that is the way you see it, here is another thought you may like to er... debate. What condemns an argument in science is not the antagonist, but its own weaknesses. Now, consider the argument that you apparently support (at least in opposition to mine, if I read you aright) that "male and female differentiation" began around or after the earliest emergence of the Chordata. Ask yourself how you would go about defending that in terms of comparative functional morphology or palaeontology. It was after all your idea, as far as I can tell, so don't bother to address my errr... opinions, just your own. But do try not to blush too deeply. After all, we all are entitled to our own pratfalls from time to time.

Next, ask yourself what reasonable arguments could be mustered to distinguish cleanly and usefully between sexual reproduction and gender differentiation, as you seem to demand. I accept that you are not going to waste your time with my views (and very wisely, if I may compliment you on your resolution in the light of the foregoing exchanges) but if you could present the forum with a cogent line of argument by which to demonstrate there could be no selection pressure for development of asymmetry in the size and mobility of gametes, and correspondingly, in the parents of the gametes, then please reveal your insights. I for one promise to receive them in a spirit of humility and praise, not to say astonishment.

You're entitled to your opinions, but present them as such unless you're willing and able to back them up immediately.

Gramercy and gramercy good sir, for the entitlement! This is no doubt the same entitlement by which you put forward your (ahem!) opinion about the squirts? And where, while we are on the subject, did you see my claiming literal and detailed special knowledge of the prehistory of the emergence of gender differentiation?

Frankly NAW, so far you are hardly presenting yourself in the best light in this exchange. Unless you shape up fast, ceasing to waste your time really seems your best option, and fast. Alternatively, if you have substantial arguments at your disposal, I'd be interested (and happy) to see them.

All the best,

Jon

 

[nismaratwork]

Well NAW, you have a nice line in emotive nomenclature. When you present an opinion I assume you call it debate or something equally urbane. When anyone disagrees and points out holes in your assumptions or reasoning, that is condemnation. Yes?
Well, if that is the way you see it, here is another thought you may like to er... debate. What condemns an argument in science is not the antagonist, but its own weaknesses. Now, consider the argument that you apparently support (at least in opposition to mine, if I read you aright) that "male and female differentiation" began around or after the earliest emergence of the Chordata. Ask yourself how you would go about defending that in terms of comparative functional morphology or palaeontology. It was after all your idea, as far as I can tell, so don't bother to address my errr... opinions, just your own. But do try not to blush too deeply. After all, we all are entitled to our own pratfalls from time to time.

Next, ask yourself what reasonable arguments could be mustered to distinguish cleanly and usefully between sexual reproduction and gender differentiation, as you seem to demand. I accept that you are not going to waste your time with my views (and very wisely, if I may compliment you on your resolution in the light of the foregoing exchanges) but if you could present the forum with a cogent line of argument by which to demonstrate there could be no selection pressure for development of asymmetry in the size and mobility of gametes, and correspondingly, in the parents of the gametes, then please reveal your insights. I for one promise to receive them in a spirit of humility and praise, not to say astonishment.


Gramercy and gramercy good sir, for the entitlement! This is no doubt the same entitlement by which you put forward your (ahem!) opinion about the squirts? And where, while we are on the subject, did you see my claiming literal and detailed special knowledge of the prehistory of the emergence of gender differentiation?

Frankly NAW, so far you are hardly presenting yourself in the best light in this exchange. Unless you shape up fast, ceasing to waste your time really seems your best option, and fast. Alternatively, if you have substantial arguments at your disposal, I'd be interested (and happy) to see them.

All the best,

Jon

I would say that the tone of your original post in response to mine and others appeared to be quite certain and, here I'll bow to your distaste for the verbosity you seem to enjoy, confrontational to the point of anger. Beyond that, the fact that you present your opinion in the form of multiple of paragraphs of polemic (ok, I do like debate) doesn't make them valid. If you can't provide some measure of substance beyond your own view and constant reference to their elementary nature, I'll say it again, this is not a worthwhile discussion. I do salute your posturing, which is done while accusing me of the same; it has an impressive timbre that really let's the reader know that you enjoy the 'sound of your own voice'. Perhaps if you want to have an actual discussion in the future you might want to adjust that to something more sotto voce.

 

[Jon Richfield]

I would say that the tone of your original post in response to mine and others appeared to be quite certain and, here I'll bow to your distaste for the verbosity you seem to enjoy, confrontational to the point of anger.

Whose anger NAW? Yours or mine? I wasn't angry. Mainly disapproving at first of your mockery in abuse of Tunicata. Confrontational? You must live in a position of considerable authority if you are so sensitive to disagreement that any propositions other than your own count as confrontation. Congratulations on your comfort zone. Bad luck when you are not at work though.

Beyond that, the fact that you present your opinion in the form of multiple of paragraphs of polemic (ok, I do like debate) doesn't make them valid. If you can't provide some measure of substance beyond your own view and constant reference to their elementary nature, I'll say it again, this is not a worthwhile discussion.

Denotional aren't we? Redundantly so? When it isn't confrontational, it is polemical, right? You do like debate? Not on the available evidence, you don't seem to; you haven't debated. Apart from some grizzling about (... sources <siiigh!>...) you have not made a single substantive statement since I mentioned the reason to believe that there was not only sex, but gender long before there were chordates, and referred to multiple kingdoms as examples. Really polemical that was... I'm oh, so ashamed...!
You of course, in your far greater scientific dignity pointed out that... errr...
What was that again, apart from the sources bit?
So far that debate of yours seems to amount to JR two or three, NAW 0, right? Now tell me again about substance?

I do salute your posturing, which is done while accusing me of the same; it has an impressive timbre that really let's the reader know that you enjoy the 'sound of your own voice'. Perhaps if you want to have an actual discussion in the future you might want to adjust that to something more sotto voce.

Confrontation, polemics, now posturing, and audible timbre without audio... more and more. Just no substance. This from the guy who began with what was it again? Diatribe? What next? Invective? Billingsgate?

As a joker, you might like to know what is funniest? I really did hope for some substance from you. Not necessarily anything beyond rational opinion, but substance. I did ask remember? "Now, let's hear your sources for the origins of "sexual division" post chordate. I won't ask you to limit yourself to first-year references..."

So much for sources!

Oh well,

Go well,
Jon

 

[jackson6612]

To Jon, Nismar

I request you both to end this. We are getting nothing out of it. You are both entitled to your opinions. There is no need for continuation of all this. Thanks for consideration.

Regards
Jack

 

[Jon Richfield]

To Jon, Nismar

I request you both to end this. We are getting nothing out of it. You are both entitled to your opinions. There is no need for continuation of all this. Thanks for consideration.

Regards
Jack

No problem. I have made my points and am not angry. I hope that Nismar feels the same way. Let's hope that future exchanges are amiable.

Cheers,

Jon

 

[jackson6612]

Thank you, Jon.

 

[nismaratwork]

To Jon, Nismar

I request you both to end this. We are getting nothing out of it. You are both entitled to your opinions. There is no need for continuation of all this. Thanks for consideration.

Regards
Jack

I'm not going to go forward to the detriment of others in this thread, and you have my apology if this has been disruptive already.

 

[nismaratwork]

To the point at hand, the thread specifically asks, "when male and female fully developed into separate and distinct...:, not "when did asexual forms of reproduction lose dominance. Some believe that early plants take that cake, http://www.msnbc.msn.com/id/27927661/

and others believe that this occurred long before plants developed. I believe that Jon and I can agree that pinpointing this kind of thing with current technology is just not possible unless, as he says, pinpointing means hundreds of millions of years. Did this occur to resist parasitism and disease in general, or was it advantageous in providing a higher rate of mutation? These remain serious unknowns. The issue of swapping genes, and gender is very different.

 

[jackson6612]

Main question:
https://www.physicsforums.com/showpost.php?p=2806381&postcount=55

The "furnace" is still working, the selection environment changed.

Alex

As we know, the life started from the non-living molecules which somehow, no one knows how, banded together to form simple proteins etc. That was the initial stage of all the life on primordial earth. I believe that initial is no longer active. The reason is the environment has changed. All that happened in primordial earth. So, I think saying that the furnace is still working is not actually correct. Mutations are taking place all the time and this gives rise to new varieties of life but the furnace which was really responsible for the life is not there now. Do I make any sense? Please guide me.

I'm not a biology student, so I request you to be plain and explain things in layman terms. Thanks.

 

[nismaratwork]

Main question:
https://www.physicsforums.com/showpost.php?p=2806381&postcount=55



As we know, the life started from the non-living molecules which somehow, no one knows how, banded together to form simple proteins etc. That was the initial stage of all the life on primordial earth. I believe that initial is no longer active. The reason is the environment has changed. All that happened in primordial earth. So, I think saying that the furnace is still working is not actually correct. Mutations are taking place all the time and this gives rise to new varieties of life but the furnace which was really responsible for the life is not there now. Do I make any sense? Please guide me.

I'm not a biology student, so I request you to be plain and explain things in layman terms. Thanks.

It's still there, although it's true that there is no longer a literal primordial ooze (well, there is some in the seabed and in labs), but that's not what evolution is all about. Evolution is an ongoing process and I'm not sure that it's possible to be alive and "turn off the furnace". Your question is phrased in such a way that to answer without refuting your premise is impossible; evolutionary pressures change, and mutations constantly occur. This has not changed from ooze, to people. As Jon Richfield has said, it's sometimes in spurts of rapid change, and as I pointed out it can be incremental and even useless! Still, one way or the other you have the furnace alive and well as long as there is life... or maybe even simple organic molecules.

 

[jackson6612]

It's still there, although it's true that there is no longer a literal primordial ooze (well, there is some in the seabed and in labs), but that's not what evolution is all about. Evolution is an ongoing process and I'm not sure that it's possible to be alive and "turn off the furnace". Your question is phrased in such a way that to answer without refuting your premise is impossible; evolutionary pressures change, and mutations constantly occur. This has not changed from ooze, to people. As Jon Richfield has said, it's sometimes in spurts of rapid change, and as I pointed out it can be incremental and even useless! Still, one way or the other you have the furnace alive and well as long as there is life... or maybe even simple organic molecules.

Hi Nismar

I have some questions. Please help me with them and also please also remember I'm a layman.

My question was more centered on the origin of life. I understand evolution is not about just the origins but still the origin is an important part.

I'm an English learner therefore I couldn't understand the part "turn off the furnace". Please help with it.

Would you mind telling me what was my premise?

In sum, are you saying that somewhere on Earth chemicals are still combining to form living chemical beings?

Thanks for the guidance.

 

[Jon Richfield]

My question was more centered on the origin of life. I understand evolution is not about just the origins but still the origin is an important part.

I couldn't understand the part "turn off the furnace". Please help with it.

I assume that Nismar will not mind my contributing part of a reply?

Hm? I thought you, Jack, asked about the furnace?

Would you mind telling me what was my premise?

Well Jack, that was part of my problem as well. I (and I think Nismar) were having difficulty understanding your intention. It can be very difficult to answer a question when one does not understand what the question was intended to mean. Sometimes it turns out not to mean what the questioner thought it meant, and that leads to real difficulty.

In sum, are you saying that somewhere on Earth chemicals are still combining to form living chemical beings?

I think what he meant (and certainly what I meant) was not necessarily that new living things are being formed from non-living chemicals. For one thing, it is possible that the conditions under which they formed on the ancient Earth are now too rare for life to be re-created, but if they are (it is quite possible in theory) then there are so many bacteria nowadays that any suitable new life molecules probably would get eaten up long before they got combined into new living things. Just think what happens to a new piece meat dropped into a pond! And that meat is far closer to life than any random molecules joining together.

But certainly some molecules that could be parts of living things if they got the chance, are being formed all the time, sometimes inorganically, sometimes as waste from living things.

 

[nismaratwork]

I assume that Nismar will not mind my contributing part of a reply?

Hm? I thought you, Jack, asked about the furnace?



Well Jack, that was part of my problem as well. I (and I think Nismar) were having difficulty understanding your intention. It can be very difficult to answer a question when one does not understand what the question was intended to mean. Sometimes it turns out not to mean what the questioner thought it meant, and that leads to real difficulty.


I think what he meant (and certainly what I meant) was not necessarily that new living things are being formed from non-living chemicals. For one thing, it is possible that the conditions under which they formed on the ancient Earth are now too rare for life to be re-created, but if they are (it is quite possible in theory) then there are so many bacteria nowadays that any suitable new life molecules probably would get eaten up long before they got combined into new living things. Just think what happens to a new piece meat dropped into a pond! And that meat is far closer to life than any random molecules joining together.

But certainly some molecules that could be parts of living things if they got the chance, are being formed all the time, sometimes inorganically, sometimes as waste from living things.

I don't mind the assist at all, and you've said everything that I would have. Jackson, if you need any help, I think it's safe to say that Jon and I can probably cover it. I might add, that for someone learning English, you sound like a native speaker; well done!

Jon, well said.

 

[Jon Richfield]

Jackson, if you need any help, I think it's safe to say that Jon and I can probably cover it. I might add, that for someone learning English, you sound like a native speaker; well done!

Yes, I must say that I too have been wondering about that. Without wishing to pry, Jack, if you don't mind telling us what languages you are master of, I for one would love to know. But if you would rather not say, please don't bother.

Jon, well said.

Thanks mate! You too.

Cheers,

Jon