How Did Sexual Organs Evolve in Mammals?

Any advances on the OP? Even after all this time, I am still puzzled at how a sperm which has never met an egg, so to speak can have evolved for an area which it would only meet during the fertilisation process. And have the correct enzymes and other proteins for:

a) neutralising the acidity of the vagina;
b) recognition of the egg and
b) the reaction where the egg closes up to only allow one sperm inside.

Is there a Natural Selection answer except for saying that we evolved from hermaphrodite worms? I would be interesting in hearing it.

Originally posted by Heronumber0
Any advances on the OP? Even after all this time, I am still puzzled at how a sperm which has never met an egg, so to speak can have evolved for an area which it would only meet during the fertilisation process. And have the correct enzymes and other proteins for:

a) neutralising the acidity of the vagina;
b) recognition of the egg and
b) the reaction where the egg closes up to only allow one sperm inside.

Is there a Natural Selection answer except for saying that we evolved from hermaphrodite worms? I would be interesting in hearing it.

I've never seen a reasonable explanation for this either. Most of it is just guesses or conjecture. Same with Ozone formation, seems to be a paradox if you approach it scientifically.

I wish I would of thought of this thread!

s&f

reply to post by B.A.C.


Thank you BAC. Much appreciated. I have seen no reasonable explanation either. However scientists consider phylogenetic studies where they match up DNA or protein sequences against each other to be scientifically rigorous evidence. If Creationists or Deists tried that they would be laughed at.

Hello again, Hero. This thread topic echoes that of another thread you authored, in which you asked how the first weaver bird came be able to 'tie the first knot'. Like that thread, this one appears to be based on an imperfect understanding of how natural selection works.

How did the sperm evolve a protective mechanism against a place (the vagina) that it has never seen before - and develop an acrosome that helps to cut through the egg?

I suppose you must get tired of hearing Darwinists bang on about it, but - yet again - evolution is not some process directed towards a predetermined end. A sperm isn't trying to evolve any more than a caddis fly or a virus is. It's simply existing, getting on with life like everything else.

It doesn't matter that a sperm has never 'seen' a vagina until it's inside one. Other sperm have met other vaginas in the past. A select few among those that survived the encounter fully functional lived to tell the tale. They told it in the form of a set of instructions for producing viable gametes contained in the DNA of the organism engendered by the sperm.

Sperms that didn't protect themselves adequately against the deadly acidity of the female tract, that didn't evolve acrosomes which produced just the right enzymes to crack an egg... those sperms never made it. Their tale remains untold. They are the silent majority, more silent than the grave, for they were never born in the first place.

So there need be no foreknowledge on the part of any sperm (or sperm-producing organism), no subcellular R&D programme designed to produce the most viable squiggly tadpoles; all that is required are a lot of mutations. The unviable ones lead nowhere, the successful ones flourish in great masses.

I know this is basic evolutionary theory, more than familiar to you. I wonder that a man of your undoubted intelligence and good faith still seems unable, despite considerable thought and debate, to grasp the basic premise that evolution is not teleological. The OP of this thread, like the weaverbird one, assumes that it is.

You asked some specific questions.

How [could] a sperm... have the correct enzymes and other proteins for:

a) neutralising the acidity of the vagina;

b) recognition of the egg and

c) the reaction where the egg closes up to only allow one sperm inside

Don't forget that sex evolved in the water, hundreds of millions of years before life crawled ashore and started breathing air. And to this day, relatively few aquatic animals copulate in the mammalian sense. More usually, gametes are ejected into the surrounding water, where fertilization takes place by accidental contact. This is the case even with quite advanced creatures like oviparous fish. Naturally, the hit-rate in this method of reproduction is very low.

You can see it wouldn't take much to improve on that process. And in fact, oviparous fish have evolved a range of behaviour to help their sperm and eggs along on that crucial first date:

In order to maximize the chances of fertilization occurring, some egg-layers attempt to maneuver their genital openings as close to each other as possible before spawning occurs, and there is occasionally contact between the fish, such as embraces with the fins.

myfishtank.net

Other species try to improve the survival chances of the fertilized eggs by depositing them in nests (Siamese fighting fish make nests of bubbles, very strange to see) or even carrying fertilized eggs or fry in their mouths, as tilapia do.

But of course, the safest and surest place for fertilization is in a purpose-built facility inside the body of one of the parents. And in time, more advanced aquatic animals (as well as sexually reproducing land animals and plants) developed such facilities. In most cases, the facility is contained within the female of the species; we call it a uterus. But in at least one aquatic species, things went the opposite way:

In sea horses, the female inseminates the male by inserting the oviduct into the male brooding pouch several times to ensure fertilization. After fertilization is complete, the female departs, and the male attaches itself to a nearby object with its tail waiting for the eggs to mature.

Reproductive Strategies in Fish

Mammal sexual evolution didn't start from scratch. Eggs, sperm, external sexual organs and the all-important internal plumbing had all been invented, and had diverged into a multitude of forms, long before we mammals came on the scene. We added our own variations, of course.

When one looks at all the hurdles evolution has overcome through this ancient history of proliferation and diversity, the three particular issues you mention - countering vaginal acidity, recognizing an egg and (on the part of the egg) the reaction that admits one and only one sperm per egg - don't seem especially difficult to me. Then again, microbiology is your special subject. Perhaps you could explain why you fixed on these in particular, out of the innumerable hurdles the evolution of sex has had to surmount?

How did the organs develop a gradual mechanism that would give a quarter vagina a selective advantage?

Even a quarter vagina, in terms of promoting fertilization in an aquatic medium, would be a considerable selective advantage on no vagina at all. A quarter (functionally speaking) of a penis, likewise.

In a later post, you responded as follows to someone who suggested (correctly) that male and female sex organs would evolve in tandem:

Originally posted by HeroNumber0
evolution in tandem was not touched upon. It is in the realms of pure speculation.

Come now, Hero. After your many conversations on the subject with melatonin and others, you must surely be aware that 'evolution in tandem' lies at the very heart of the modern synthesis. An organism's environment, which is the source of all selective pressure, includes the extended phenotypes of other organisms of its own species and all other species too. All species evolve, if not in tandem with others, then at least in complementary ways. It cannot be otherwise.

* * *

If you really want to get us evolutionists scratching our heads and humming and hawing, the question to ask is not 'how did sex evolve?' but 'why did sex evolve?' This briefing note from Brown University in the USA shows you just how provisional current theories are. Enjoy the read, and good luck with your efforts to falsify evolutionary theory. What does not kill us makes us strong.

Astyanax - nice to hear from you again. Hope you are well. I know that I am using the teleological argument but remember that I am also discussing ontological fortuitousness as well as the teleology.

I suppose you must get tired of hearing Darwinists bang on about it, but - yet again - evolution is not some process directed towards a predetermined end. A sperm isn't trying to evolve any more than a caddis fly or a virus is. It's simply existing, getting on with life like everything else.

From your viewpoint of course life has no eventual purpose. But what if there is a point to life and it is to read the Mind of God? What about the possibility, Asyanax, that Hegel was right and that in his dialectic the Absolute is expressing His character through the development of Creation. You see, most of the people that defend the Creationist view on this Forum are actually open to the idea of some evolution.

It doesn't matter that a sperm has never 'seen' a vagina until it's inside one. Other sperm have met other vaginas in the past. A select few among those that survived the encounter fully functional lived to tell the tale. They told it in the form of a set of instructions for producing viable gametes contained in the DNA of the organism engendered by the sperm.

Asty old boy, how does one select for an invagination or a protrusion in terms of Natural Selection? All speculation at present but it would have to be vital to the survival of the species. So the invagination would have to be tiny and then slowly grow into a vagina - we are talking about a complex organ here - not a simple cell layer.

Sperms that didn't protect themselves adequately against the deadly acidity of the female tract, that didn't evolve acrosomes which produced just the right enzymes to crack an egg... those sperms never made it. Their tale remains untold. They are the silent majority, more silent than the grave, for they were never born in the first place.

Here we go again... It seems obvious, but unfortunately it is not. A sperm has mitochondria, a tail, microtubules in the tail and a head which has a portion devoted to exactly the correct enzymes that are needed to break down the outside layer of the egg. Now I would be willing to believe that all of this occurred purely by sheer mutation and selection but for the complexity. The sheer complexity of the sperm is mind-boggling. It is difficult to see how it could be gradually see how it could be selected for in tiny steps millions of times until it becomes perfect for mammals - unless it is pushed by an 'invisible hand.' Also, did you realise that Sertoli cells are required to shape the sperm cell until maturity and that large mutations would have to affect both together?

I know this is basic evolutionary theory, more than familiar to you. I wonder that a man of your undoubted intelligence and good faith still seems unable, despite considerable thought and debate, to grasp the basic premise that evolution is not teleological. The OP of this thread, like the weaverbird one, assumes that it is.

I feel exactly the same about you Asty, you are a man of undoubted excellent intelligence yet you believe that a series of chance events could lead to the formation of life through the Law of Natural Selection without ever wondering how the Law came about in the first place.



[edit on 30/3/2009 by Heronumber0]

reply to post by Astyanax

You asked some specific questions.


How [could] a sperm... have the correct enzymes and other proteins for:

a) neutralising the acidity of the vagina;

b) recognition of the egg and

c) the reaction where the egg closes up to only allow one sperm inside

from Astyanax
Don't forget that sex evolved in the water, hundreds of millions of years before life crawled ashore and started breathing air. And to this day, relatively few aquatic animals copulate in the mammalian sense. More usually, gametes are ejected into the surrounding water, where fertilization takes place by accidental contact. This is the case even with quite advanced creatures like oviparous fish. Naturally, the hit-rate in this method of reproduction is very low.

You can see it wouldn't take much to improve on that process. And in fact, oviparous fish have evolved a range of behaviour to help their sperm and eggs along on that crucial first date:


In order to maximize the chances of fertilization occurring, some egg-layers attempt to maneuver their genital openings as close to each other as possible before spawning occurs, and there is occasionally contact between the fish, such as embraces with the fins.

myfishtank.net

Other species try to improve the survival chances of the fertilized eggs by depositing them in nests (Siamese fighting fish make nests of bubbles, very strange to see) or even carrying fertilized eggs or fry in their mouths, as tilapia do.

But of course, the safest and surest place for fertilization is in a purpose-built facility inside the body of one of the parents. And in time, more advanced aquatic animals (as well as sexually reproducing land animals and plants) developed such facilities. In most cases, the facility is contained within the female of the species; we call it a uterus. But in at least one aquatic species, things went the opposite way:


In sea horses, the female inseminates the male by inserting the oviduct into the male brooding pouch several times to ensure fertilization. After fertilization is complete, the female departs, and the male attaches itself to a nearby object with its tail waiting for the eggs to mature.

Some great research here Astyanax. It shows the marvel of variation of reproductive strategies in fish. I know where you are going with this of course - you are going to suggest a common aquatic ancestor...

from Astyanax

Reproductive Strategies in Fish

Mammal sexual evolution didn't start from scratch. Eggs, sperm, external sexual organs and the all-important internal plumbing had all been invented, and had diverged into a multitude of forms, long before we mammals came on the scene. We added our own variations, of course.

Of course, this is the conventional view and seems quite plausible until we consider this in a bit more detail. You see mutations tend to be deleterious. Mutations tend not to dominate a population unless there is an extreme condition which then pushes the bell -shaped curve of mutations in one direction or the other. You would need to explain how a small mutation or a tiny almost imperceptible change presents a life or death change for an organism. You see, Astyanax, the vast majority of human mutations are deleterious. To propose a change which turns a small vaginal flap into another with an extra layer of cells and then suggest a survival advantage does not cut the mustard for me.

When one looks at all the hurdles evolution has overcome through this ancient history of proliferation and diversity, the three particular issues you mention - countering vaginal acidity, recognizing an egg and (on the part of the egg) the reaction that admits one and only one sperm per egg - don't seem especially difficult to me. Then again, microbiology is your special subject. Perhaps you could explain why you fixed on these in particular, out of the innumerable hurdles the evolution of sex has had to surmount?

Again, you would say teleology but I could not get my head round the situation where a cell has evolved to be successful in this way unless all the correct features are in place. 2 out of three will not do.

If you really want to get us evolutionists scratching our heads and humming and hawing, the question to ask is not 'how did sex evolve?' but 'why did sex evolve?' This briefing note from Brown University in the USA shows you just how provisional current theories are. Enjoy the read, and good luck with your efforts to falsify evolutionary theory. What does not kill us makes us strong.

I think my puzzle is also why sexual reproduction goes to the effort of halving the amount of DNA by meiosis when it would be easier just to carry out parthenogenesis instead which is far easier and involves a simple chromosome duplication event. As a result, favourable environmental conditions would generate a large number of genetically identical organisms. Simple and straightforward yet evolution apparently chose the harder route to meiosis.

Astyanax thank you for the post. I will read the links as soon as possible.

reply to post by Heronumber0

Well, then, Hero it seems we are at something of an impasse. Your difficulties with the evolution of sex organs are basically the same as your general difficulties with evolutionary theory.

The most important is that you have trouble believing that complex living systems can evolve in the first place.

A sperm has mitochondria, a tail, microtubules in the tail and a head which has a portion devoted to exactly the correct enzymes that are needed to break down the outside layer of the egg. Now I would be willing to believe that all of this occurred purely by sheer mutation and selection but for the complexity. The sheer complexity of the sperm is mind-boggling.

Since a sperm is no more complicated than an ordinary cell, I assume your argument from complexity applies to them too. Like all subscribers to the theory of evolution, I don't find it convincing. The amazing complexity and variety of life does not dissuade me that evolution by natural selection, undirected by any willing agent, is true.

Your second objection, a child of the first, is that you find specific adaptations hard to wrap your head round.

How does one select for an invagination or a protrusion in terms of Natural Selection?

Starting from an ordinary orifice? I really don't see the problem, especially in an aquatic environment. Any cache or depression would help with fertilization of ova; any adaptation that would fit such a depression or cache would help, too. That's enough, at least to my mind. This is the argument usually summed up by creationists in the oft-repeated (and long exploded) objection to the evolution of the eye.

I really have nothing more to add.

Originally posted by Astyanax
reply to post by Heronumber0

 

Well, then, Hero it seems we are at something of an impasse. Your difficulties with the evolution of sex organs are basically the same as your general difficulties with evolutionary theory.

The most important is that you have trouble believing that complex living systems can evolve in the first place.

It is not that Asty, it is the sheer incredible complexity we see around us. Can mutation, variation then selection by fitness through behaviour or phenotype (feature) really explain it. Can it also explain the huge number of people who have experienced the Near Death Experiences I have outlined in another Thread? There seems to be something out of the ordinary happening when we shrug off our mortal coils. If Science does not believe it then it needs to disprove it by experiment.

by Astyanax
Since a sperm is no more complicated than an ordinary cell, I assume your argument from complexity applies to them too. Like all subscribers to the theory of evolution, I don't find it convincing. The amazing complexity and variety of life does not dissuade me that evolution by natural selection, undirected by any willing agent, is true.

Asty, let's say that I agree with the idea of the sperm and egg evolving from aquatic life and then by selection and mutation ending up enclosed in mammals, you would still be left to explain how the small changes happened by random mutation then selection. To be honest even that is mind boggling. The sheer complexity of a cell membrane on its own, with the specificity that it shows can keep a team of scientists occupied for a lifetime yet we are dismissing the evolution of cell membranes in a few lines. Do you see what I mean?

by Astyanax Your second objection, a child of the first, is that you find specific adaptations hard to wrap your head round.

How does one select for an invagination or a protrusion in terms of Natural Selection?

Starting from an ordinary orifice? I really don't see the problem, especially in an aquatic environment. Any cache or depression would help with fertilization of ova; any adaptation that would fit such a depression or cache would help, too. That's enough, at least to my mind. This is the argument usually summed up by creationists in the oft-repeated (and long exploded) objection to the evolution of the eye.

I really have nothing more to add.

First of all I must say that you were the first person to actually attempt to provide a thorough scientific platform for the evolution of sperm and egg and that is quite notable on its own. However, to nuts and bolts.
In the above example, you see it through the eyes of a person looking at the ultrastructure and saying: 'Well that wasn't too difficult wasn't it?' However, I am viewing it from the viewpoint of molecular interactions and I can see the astonishing complexity and frankly astonishing events that must have taken place. I will get to the point. Let's say that we miss out the genesis of the single cell as a complete entity capable of self replication without being selected out by the vicissitudes of Nature. The next problem is self assembly. A set of events all selected for after mutation would have to evolve a set of protrusions on the cell surface to allow the formation of tissue. Then another set of mutations would have to be selected by Mother Nature to build another layer of tissue. I do not know of a selection procedure which after random genetic drift and selection would cause extra cells to be selected for because they provide a selective advantage. If anything, the single cells have a distinct advantage in asexual reproduction to avoid all the hassle of waiting a million years to be selected for. Then another layer of cells would have to develop cell by cell with selection by survival. I have no idea of such a mechanism. This is at the heart of my objections to be honest.

This is a very good thread. Ultimately it booils down to Evolutionary Theory vs. Creationism. I believe there are arguments for and against both.

I believe it is more probable, that evolutionary theory is correct, whilst there is also intelligent design. Evolutionary theory states many things happen due to mutations of genes etc. However, what I would put to you is, how the HELL did bacteria evolve into a multi-cellular organism with the ability to Orgasm.

Where in nature did it have the idea to "reward" those that try to reproduce? Where/How did that mutation come to be?

Its almost like teaching a toddler that 1+1 = 2 and they figure out A^2 + B^2 = C^2.

Originally posted by Toughiv
Where in nature did it have the idea to "reward" those that try to reproduce?

Good question. Have you heard of a concept in physics called symmetry breaking? In an ontological sense you might say it came from there.

But nature doesn't have ideas. What happened is that the neurophysiological apparatus of pleasure evolved slowly, bit by bit, driven by natural selection because those organisms who enjoyed sex had more offspring than the ones who didn't. The real question is your second one:

Where/How did that mutation come to be?

That - the 'how', not the 'where' - is HeroNumber0's question, too. Though his objections are really to do with the huge number of mutations that must have taken place. I don't have Hero's specialized knowledge of biochemistry, but if the overwhelming majority of biochemists feel there's no issue, that's good enough for me.

Ross Perot said they evolved , "From that giant sucking sound."

Guys please dont stop. Ive learnt more from this thread than from reading 20 books. I want to believe in natural selection and chance mutation but certain things life the sexual organs keep baffling me. I mean chance is chance and the chances here are almost impossible even miraculous u could say. One thing on this thread that caught my attention was that

An organism's environment, which is the source of all selective pressure, includes the extended phenotypes of other organisms of its own species and all other species too. All species evolve, if not in tandem with others, then at least in complementary ways. It cannot be otherwise.

is this a fact or just an hypotheses. For me it makes sense only from other articles ive read into metaphisics about a collective conscious. Maybe we do evolve in tandem due to us being connected to a universal collective conscious. This could also answer why species developed in all corners of the world simultaneously like the cambrian explosion..

Other articles ive read talks about the law of attraction and power of the will. Maybe we will ourselves and thus our biology to something we want and need. This hypothesis seems to be pretty logical not only from an atheist point of view but also a creationist. Maybe its not inteligent design by a God like entity but rather designed and created by us through our will and collective conscious. This also favours atheist for it doesnt evolve any seperate entity other than our selves.

Just something that ive been pondering on for some time now and makes sense to me but then again im no expert on these matters.

Here's my take on this.

Variety is an evolutionary advantage. Sexual reproduction leads to exponential variety because of the combination of two entirely different histories of DNA sequencing.

My guess is that early organisms developed both DNA receptors and DNA injectors. Those organisms that developed both had an evolutionary advantage over those that didn't.

Next, organisms that developed ONLY one type of DNA organ, a receptor or injector, had an evolutionary advantage because those organisms were assured diversity. I.e., they could not reproduce asexually.

Here's another way to look at it:

Simple asexual reproduction, like a Xerox machine copying papers, is GUARANTEED to produce organisms that will die off and never be seen again because there is no means for adaptation. Sexual reproduction guarantees diversity, and therefore guarantees an evolutionary advantage. A penis and vagina guarantee diversity.

It also means that the sex organs of every female/male animal and human on earth some how developed in perfect parallel, and then once than parallel was complete, they all just copulated on instinct that suddenly implanted itself in them all.

Another question as these organs were evolving but not yet ready for reproduction how were they reproducing ?
Was not asexual reproduction actually better for the species ?
As you never needed to find another partner to reproduce ?

This part of the theory makes no sense.

they dont know thats there reply they have no clue its a lie

its magic Alice in wonderland stuff

Originally posted by sconner755
Here's my take on this.

Variety is an evolutionary advantage. Sexual reproduction leads to exponential variety because of the combination of two entirely different histories of DNA sequencing.

My guess is that early organisms developed both DNA receptors and DNA injectors. Those organisms that developed both had an ty volutionary advantage over those that didn't.

Next, organisms that developed ONLY one type of DNA organ, a receptor or injector, had an evolutionary advantage because those organisms were assured diversity. I.e., they could not reproduce asexually.

Here's another way to look at it:
sorry evolution has no facts in history none a man cant give birth to a cat nor a women can give birth to a cat you lie
Simple asexual reproduction, like a Xerox machine copying papers, is GUARANTEED to produce organisms that will die off and never be seen again because there is no means for adaptation. Sexual reproduction guarantees diversity, and therefore guarantees an evolutionary advantage. A penis and vagina guarantee diversity.

you need to show us these life talk is crap show us it

the organs that fit best, where by this mechanism naturally propagated.

show us talk is crap you notice how did a rat turn into am man from rat to man a simple q

let me make things easy for you kids show me how life did not die from a rat to a man you say a rat turned into a ape then a man how magic please show prof use DNA like we can with mother eve in search of eve