Difficulty understanding evolution

[Vanadium 50]

By the time that the first fish species evolved, sexual reproduction had already been in place a long time.

True. A very long time. Around the time of the common ancestor of plants and animals, 1.2 billion years ago. Fish are only about 500 million years old.

 

[rootone]

Sexual reproduction must have initially been one of those lucky mutations.
Before that, and still now, there are many organisms which have their niche and are doing fine without it.
Once that exists though, evolution probably speeds up, more variables to play with.

 

[Drakkith]

Sexual reproduction must have initially been one of those lucky mutations.

Not just one of those lucky mutations, but a lot of "lucky" mutations acted upon by natural selection. That may seem like it's very unlikely to some, and it certainly is, but natural selection had several billion years to build up to that point. Trillions upon trillions upon trillions of fast-reproducing cells and a couple billion years over which to act is a lot of chances.

 

[Jon Richfield]

Not just one of those lucky mutations, but a lot of "lucky" mutations acted upon by natural selection. That may seem like it's very unlikely to some, and it certainly is, but natural selection had several billion years to build up to that point. Trillions upon trillions upon trillions of fast-reproducing cells and a couple billion years over which to act is a lot of chances.

To me that seems to under-emphasise the non-stochastic nature of evolution, "evolutionary opportunism" building upon the nature of what had gone before. (I don't like the use of the term "heuristic" in this connection, because to me that suggests something too teleological).

I suspect that sexual reproduction was a by-product or consequence of the nature of duplication of nucleic acid by chain sequence matching and of cell formation and division at the time when the first cellular life was evolving. I suspect furthermore that it was preceded by phases where cell materials were rather freely exchanged and the concept of "species" was not yet well-defined. (Not that IMO it is all that cleanly defined nowadays, but let that be for the moment!)

 

[Drakkith]

To me that seems to under-emphasise the non-stochastic nature of evolution, "evolutionary opportunism" building upon the nature of what had gone before. (I don't like the use of the term "heuristic" in this connection, because to me that suggests something too teleological).

I'm not sure what you mean by this. Can you elaborate?

I suspect that sexual reproduction was a by-product or consequence of the nature of duplication of nucleic acid by chain sequence matching and of cell formation and division at the time when the first cellular life was evolving.

Sexual reproduction is thought to have evolved around 1.2 billion years ago. Life is thought to have arisen well over 3 billion years ago. Cellular life was around long, long before sexual reproduction evolved.

 

[Jon Richfield]

I'm not sure what you mean by this. Can you elaborate?

"Stochastic" in this sense would suggest that just any mutation in any organism would be equally likely and equally evolutionarily significant, like starting over with a new toss of a hatful of type every time it doesn't come out reading like a page of Shakespeare.
"Heuristic" would be like tossing again mostly the letters that didn't match the page.
Evolution by natural selection is more like the latter, but not much like either, because it is not teleological; there IS NO page to match for a foreknown and desired, or notionally correct outcome. ANY outcome that serendipitously improves successful reproduction rates (ie increases "fitness") represents progress in the short term, though in the longer term it might be disastrous.
So for example, a more muscularly competitive male or one better endowed with an impressive fertilisation mechanism might be the result of advantageous to a male in a particular generation. (It might prove disastrous later, but that is a problem for the teleologist.) But the same mutations might prove useless a hundred million years earlier, when say, muscles or intromission were irrelevant to reproduction.

Does that help?

Sexual reproduction is thought to have evolved around 1.2 billion years ago. Life is thought to have arisen well over 3 billion years ago. Cellular life was around long, long before sexual reproduction evolved.

Good luck; never mind demonstrating that, good luck just stating it meaningfully -- ask yourself what form the original sexual reproduction might have taken!

What do you mean by sexual reproduction? Virile males and complaisant females with functionally conspicuous secondary sexual features to match each gender? Long before anything of the type emerged, before even distinct gametes had evolved in prokaryotes, let alone eukaryotes, the genetic functions of nucleic acid reading for gene expression had existed, and probably even before that, reproduction of nucleic acid chains by base-pair matching. (Think out the information theory of the process!) Even today the expression of genetic information in prokaryotes is not all that well distinguished from reproduction.

Now, what is the essence of sexual reproduction; not the variety and mechanism of genders: it is a variable set of aspects of:

1. Given an organism that has an adequate genome, (typically in the form of paired NA chains, so I'll ignore any other form here, though that is not necessarily the only possibility) the organism can split the paired chains apart for reading, either for expression or duplication. In its simplest form this is "asexual" reproduction, such as in somatic cells or monocellular organisms.
2. An elaboration or in fact possibly a degeneration of that very mechanism could match the paired chains in the organisation of the first approach to chromosomes in the modern sense. This could have been very helpful in permitting primitive, asexual, forms of chromosomal reproduction; cells could thenceforth "tell" whether their own or daughter chromosome complements were complete, in contrast to some viruses such as flu.
3. A separated, but coordinated mechanism would be necessary for cell division, or we simply would wind up with a mass of undifferentiated cytoplasm stuffed with chromosomes or perhaps ancestral forms of chromosomes.
4. Inverse forms of division of cells and matching of chromosomes would lead to the merging of cells and matching of their genetic material. this would amount to a primitive form of fertilisation. Note that a key aspect of this form of combination would amount to the formation of a diploid zygote from two haploid cells or gametes.
5. To correct this condition that otherwise must lead to runaway polyploidy; we need a form of division that would halve the diploid chromosome complement to reinstate the haploid state, and precisely that is what meiosis means: reduction (commonly called reduction division).
6. That is what sexual reproduction amounts to. All the rest, genders, manes on lions, penes in males, special forms of gametes (anisogamy instead of isogamy) are frills; frills arising repeatedly in innumerable forms in response to selective pressures. It is the frills that began to become arguably detectable about 1 - 2 GY BP. Sexual reproduction was something like twice as old at a guess; maybe more.

I have a nasty feeling that I have forgotten a couple of books' worth, but it is a big subject, the realities are speculative, and I suspect that you time is not much less at a premium than mine, so if I have omitted anything disastrously, please let me know.

 

[Ryan_m_b]

General mod note: there's been a lack of references for a while, that was ok when we were covering the very basics but if the thread is trending towards the evolution of specific traits PF rules on citations become more important.

 

[Adamchiv]

General mod note: there's been a lack of references for a while, that was ok when we were covering the very basics but if the thread is trending towards the evolution of specific traits PF rules on citations become more important.

I think that we are dealing with each issue as it comes, this specific issue has become deeper but I think we are on the cusp of resolving it and moving into another sub topic. As the original poster I feel that this is leading very nicely through each specific query. Though I am certainly not the authority on here this is just my opinion

 

[BillTre]

Sexual reproduction is usually considered to have the following cycle whenever reproduction occurs:
1) diploid cells (having two sets of chromosomes) divide to reduce the number of chromosomes to half (haploid)
2) the fusion of two complementary haploid cells to restore the resulting fused cell to the diploid state

Functionally important for this are:
-eukarote chromosomes (linear chromosomes with teleomeres), https://en.wikipedia.org/wiki/Centriole
-pairing of homologous chromosomes to facilitate crossing over,
-cell division mechanisms that ensure the right chromosomes go to the right cell during division
The cell division mechanisms involve centrioles (spindle organizers), a spindle containing microtubules on which the chromosomes move during division and that is involved in cell division, and centromeres on chromosomes that attach them to the spindle so they can be moved to one of the daughter cells.
This is suite of features is found in almost all sexually reproducing organisms, except that some plants and fungi can do without the centrioles.

This is distinguished from the situation in many bacteria, where they have a circular chromosome (which is structurally simpler) and most reproduction involves duplicating the chromosome followed by cell division such that each daughter cell gets a chromosome.
Bacteria can exchange DNA and increase their genetic variability by mechanisms like conjugation, but this is not something that happens every time the organism reproduces and it does not mix whole genomes. It is thus an occasional mixing event compared to sexual reproduction.

Genes genetically linked together on a parental chromosome have the opportunity to break their linkage to neighboring genes and acquire new neighbors. This results in greater diversity in the genetics of the offspring because an important aspect of diversity is in the diversity of different gene combinations.

Most sexual organisms use sexual reproduction whenever they reproduce, however, some cases (such as hydras) can bud off of new organisms in a non-sexual way.
This results in a clonal derivative of the organism's somatic cells. No genetic differences from the parents.
Asexual reproduction can be a faster way to reproduce in a very permissive environment where the organism is thriving, not stressed and apparently doesn't need a genetic recombination to create potentially more adaptive genetic combinations. Asexual reproducers can often also reproduce sexually, in less optimal conditions, so that their offspring are produced with the possible genetic benefits of genetic recombination. Aphids can do this kind of thing.
Some animals have lost sexual reproduction completely (such as Bdellid rotifers and some fish and reptiles).

In animals, the haploid cells are the reproductive cells and the diploid cells are the somatic cells (most of the other cells in the body). In some fungi and plants the relationship is reversed (adults haploid, reproductive cells diploid), but because the above cycle is still used, its still sexual reproduction and results in a greater diversity of gene combinations.

As stated above:

Sexual reproduction is thought to have evolved around 1.2 billion years ago. Life is thought to have arisen well over 3 billion years ago. Cellular life was around long, long before sexual reproduction evolved.

this complex suite of features required for sexual reproduction probably arose in a common ancestor of plants, animals, fungi and protists (single celled eukaryotes). Eukaryotes have linear chromosomes, and a cell division mechanism to deal with them properly.

The original post was about sexual organs, not sexual reproduction, but an understanding of sexual reproduction underlies it.
Sexual organs are there because of the occurrence of sexual reproduction. Sexual organs support the production and survival of the specialized sex cells (internal sexual organs). Sexual organs (external gentalia mostly) are involved in delivering the male haploid genome (sperm in animals) to the female's reproductive cells (eggs in animals) for fertilization. These organs probably evolved later as reproductive mechanisms became more complicated and sex cells in metazoans become more specialized. Early fish-like-things (and some fish today) for example, just released gametes into the ocean where they largely rely on chance to find and combine complementary gametes. The delivery system is minimal, but the cells still reside in testes and ovaries.

 

[Adamchiv]

There is certainly enough detail in these previous posts to form a detailed understanding, I thank you all for such in depth analysis, it will take me a while but I think I can find some foundation there for sure. Could we discuss (and this may sound crude or silly) the mental stimulation involved in evolutionary reproduction, for example, I can't think of which animal it is but there are animals that are dying out because they don't want to mate. So first question is why do they lose their libido, second question is regarding stimulation, to get to a positive stimulation in reproduction is that trial and error? For example those that got a positive stimulation were more likely to reproduce? Because it doesn't exactly feel horrible does it and there are obviously very positive urges that can't have just "been" it must have been an evolutionary trait right? Hate to get into these crude things but again its part of the whole development of life without any conscious design that I would really like to understand

 

[rootone]

Have you heard of Occam's razor?
It's rule of thumb which says the simplest idea is most likely to be right.
https://en.wikipedia.org/wiki/Occam's_razor
When you start introducing intention of some 'thing' to make the Universe and life what it is,
then you have a whole load of explaining to do as to how that 'thing' got to exist in the first place.
.

 

[Drakkith]

So first question is why do they lose their libido, second question is regarding stimulation, to get to a positive stimulation in reproduction is that trial and error? For example those that got a positive stimulation were more likely to reproduce?

For organisms that don't want to mate, the catchall reason would be because of "stress". That stress can be because of shortages of food and water, population pressure, disease, captivity, and countless other reasons.

Because it doesn't exactly feel horrible does it

For some species, mating is extraordinarily painful, stressful, or even fatal. For example, male bed bugs stab the female through the exoskeleton and release their sperm into the female's body, where it is transported through the hemolymph to the ovaries. In some species (such as some mantises), the male is sometimes eaten after mating.

and there are obviously very positive urges that can't have just "been" it must have been an evolutionary trait right?

Yes, but narrowing it down to some specific reason that the trait was selected for is usually very difficult. What may seem like a huge negative, like being eaten after mating, can actually be beneficial to the survival of the organism's genes (a well-fed mate is more likely to survive and pass on your genes than a hungry one).

 

[eltodesukane]

An interesting reference (a bit off topic):
About domesticating foxes by human/natural selection (like wolves were domesticated to become dogs over thousands of years)
"In the 1950s a Soviet geneticist began an experiment in guided evolution. He wanted to show how domestication works"
http://www.bbc.com/earth/story/20160912-a-soviet-scientist-created-the-only-tame-foxes-in-the-world

 

[Adamchiv]

An interesting reference (a bit off topic):
About domesticating foxes by human/natural selection (like wolves were domesticated to become dogs over thousands of years)
"In the 1950s a Soviet geneticist began an experiment in guided evolution. He wanted to show how domestication works"
http://www.bbc.com/earth/story/20160912-a-soviet-scientist-created-the-only-tame-foxes-in-the-world

Thats on topic for me, because I think that domestication over time is further proof of evolution. I wonder how information is preserved and passed down from generation to generation. On a basic level, instinct. I suppose its proof that the brain is a physical organism that works within itself and the soul is a stupid concept. Because everything within us is physical in some form, surely on a quantum level the instinct passed down from generation to generation must be observable in some sense, it must be detectable as some sort of neurological bar code or something

 

[Drakkith]

Instinct doesn't work on the quantum scale. It is the result of the particular way systems of neurological cells are connected to each other in an organism.

 

[BillTre]

Domestication is a very interesting subject. A lot is known about it.

The information determining the instinctive behaviors is genetically encoded within the animal's genome.
This is information in the order of the base pairs in the DNA double helix, as interpreted by the cellular environment in which it resides. Its not a quantum level thing.

That Genetic Information would then direct the development of the nervous system to make those neural connections mentioned by @Drakkith. This is a complex process working through a variety of encoded developmental processes.
Environmental Information: Some of the development would be influenced by general environmental sensory input (for instance to refine the visual map), but that would be refining the genetically determined developmental processes that set-up these refinements.
Culturally Inherited Information (among the domesticated) does not seem to be important since domesticated animals (or plants) don't have to be raised in groups to express their domesticated traits.

 

[Adamchiv]

Domestication is a very interesting subject. A lot is known about it.

The information determining the instinctive behaviors is genetically encoded within the animal's genome.
This is information in the order of the base pairs in the DNA double helix, as interpreted by the cellular environment in which it resides. Its not a quantum level thing.

That Genetic Information would then direct the development of the nervous system to make those neural connections mentioned by @Drakkith. This is a complex process working through a variety of encoded developmental processes.
Environmental Information: Some of the development would be influenced by general environmental sensory input (for instance to refine the visual map), but that would be refining the genetically determined developmental processes that set-up these refinements.
Culturally Inherited Information (among the domesticated) does not seem to be important since domesticated animals (or plants) don't have to be raised in groups to express their domesticated traits.

But if you take an individual memory, its a very complex image or mental video, surely it must be stored in the mind as a type of data? Its in there and can be accessed, its unique too, so as a stored unique thought, surely it must have some sort of a pattern or code etc

*maybe this is for another thread

 

[Adamchiv]

Its ok I've just looked into how memories are stored and I don't think I need to discuss it on this thread and also its going to get off topic.

Can we continue about domestication being passed down, because it is interesting

 

[BillTre]

Instinct is a kind of behavior.
It doesn't have in involve memory.
Most instincts (in lower animals) can be thought of as actions, perhaps in response to a sensory input, in a particular environment.
This can just be built into a nervous system when it develops.

Not all domestication traits are behavioral.
http://www.maizegenetics.net/genetics-of-domestication in corn deal with things like number of seeds, attachment to stem, etc.

 

[Adamchiv]

Instinct is a kind of behavior.
It doesn't have in involve memory.
Most instincts (in lower animals) can be thought of as actions, perhaps in response to a sensory input, in a particular environment.
This can just be built into a nervous system when it develops.

Not all domestication traits are behavioral.
http://www.maizegenetics.net/genetics-of-domestication in corn deal with things like number of seeds, attachment to stem, etc.

But the baby kangaroo climbs up into the pouch when its born, this is literally its first moments. There must be some instinct passed on, it can't be tought

 

[Drakkith]

But the baby kangaroo climbs up into the pouch when its born, this is literally its first moments. There must be some instinct passed on, it can't be tought

That's right. Instinct is stored and passed on in the genetic information of the organism. It is, by definition, complex behavior that doesn't have to be learned. Note that instinct isn't "hard coded" into the genome. There is no gene in sea turtles that says, "Okay, when you're done hatching and you see water, run towards it as fast as you can!" Instead, genes contain information having more to do with protein structure, timing of molecular signals, and regulatory sequences (e.g. promoters, enhancers, and silencers that affect the rate of transcription of that particular gene). The combination of many different genes governs the overall development of the organism and this initial development sets up the neurological and chemical "circuitry" that governs how the organism's instincts function.

Can we continue about domestication being passed down, because it is interesting

Domestication itself isn't something that's passed down. To quote wikipedia, "Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that second group."

However, the traits that we usually select for when domesticating animals or plants are indeed passed on to subsequent generations in exactly the same ways that any other trait is passed down. The only difference is that we are doing the selection instead of nature. If you haven't already, take a look at the following article: https://en.wikipedia.org/wiki/Selective_breeding

 

[BillTre]

But the baby kangaroo climbs up into the pouch when its born, this is literally its first moments. There must be some instinct passed on, it can't be tought

Yes it is passed on, genetically.

 

[houlahound]

The silver fox experiment showed interesting traits re domestication. In the op you mentioned atheism and evolution, they are unrelated concepts. Why did you mention them together?

Not all mammals find their way to suckle, puppies that don't die within 24 hours unless hand fed.

I train working dogs, the traits that make them work contradict domestication. Its a balancing act of selective breeding to push traits back or bring them forward. The whole thing is fluid, there is no steady state.

 

[Drakkith]

In the op you mentioned atheism and evolution, they are unrelated concepts. Why did you mention them together?

Just a note for everyone: Let's stick to the topic of evolution, please. I've already had to remove one post that veered off into religious matters. Further off-topic posts may result in a locked thread. I hate to remove posts for this reason, but they're off topic and experience has shown that people tend to get very, very heated when it comes to religious matters, and discussions tend to fly out of control very quickly.

 

[BillTre]

I train working dogs, the traits that make them work contradict domestication.

What is this contradiction you speak of?
Is it a general affect or something specific to the task they are being trained for?

 

[houlahound]

It's a lot of splaining, in a nutshell a dog's survival instincts a what we can exploit for work, too much and the dog is unworkable, too little and the dog is a useless lawn ornament.

Modern society selects for the dull, useless lawn ornament with no sense of survival. Interestingly the demand for working dogs in the agencies is sky rocketing but the pool is almost empty.

Did you see the Whitehouse dogs fail? That right there shows the contradiction in full. Those dogs had no defense drive, no dominance, and failed because of it.

The harder dogs would not have got the job to start with being too offensive but were what was required in that instant.

My current idiot dog would have had to been choked off the guy and would have gone after the handler because he would have perceived the handler was challenging him, too much the other... see the contradiction?

Conversely when the balance is right you get the dog that got Osama with SEAL team 6. Those dogs are rarer than hen's teeth.

 

[stevendaryl]

I confess to not having read this entire thread, so I'm not sure if I'm saying something redundant, but the original poster is making a false assumption about the way that genetics controls the physical form of a creature. (I think the jargon is: how genotype influences phenotype). Random mutations do not lead (usually) to random bumps and appendages. Genes don't specify precisely what goes where on your body. Instead, their control over your body is very indirect--they (mostly? completely?) specify the presence or absence of certain proteins produced by your cells. The impact of these proteins is very indirect. Much of the development of a vertebrate should be thought of in the following way:

• There is a basic plan for a vertebrate: A spine, a head containing a brain, two eyes, and a mouth at one end of that spine, approximate bilateral symmetry, a heart, blood vessels, a stomach, etc.
• Genes mostly just tweak this basic plan. They enlarge some parts, shrink other parts, fuse parts, split one part into two, etc.

So you're not likely to have a mutation to a vertebrate that would make a second head at its knee, or have a third arm growing out of the back of its neck. If a genetic mutation is too extreme, by far, the most likely outcome would be that the creature would fail to live long enough to be born.

 

[Ryan_m_b]

I confess to not having read this entire thread, so I'm not sure if I'm saying something redundant, but the original poster is making a false assumption about the way that genetics controls the physical form of a creature. (I think the jargon is: how genotype influences phenotype). Random mutations do not lead (usually) to random bumps and appendages. Genes don't specify precisely what goes where on your body. Instead, their control over your body is very indirect--they (mostly? completely?) specify the presence or absence of certain proteins produced by your cells. The impact of these proteins is very indirect. Much of the development of a vertebrate should be thought of in the following way:

• There is a basic plan for a vertebrate: A spine, a head containing a brain, two eyes, and a mouth at one end of that spine, approximate bilateral symmetry, a heart, blood vessels, a stomach, etc.
• Genes mostly just tweak this basic plan. They enlarge some parts, shrink other parts, fuse parts, split one part into two, etc.

So you're not likely to have a mutation to a vertebrate that would make a second head at its knee, or have a third arm growing out of the back of its neck. If a genetic mutation is too extreme, by far, the most likely outcome would be that the creature would fail to live long enough to be born.

All generally correct, though mutations can occur that lead to gross physical changes (such as hox gene mutations, though I'm unsure how drastic they were in the wild vs the lab) they tend not to. One of the sticking points the OP had was difficulty keeping in mind that mutations tend to be very minor and evolution happens across long time scales. Anecdotally I've found this a very common confusion amongst non-biologists.

 

[stevendaryl]

All generally correct, though mutations can occur that lead to gross physical changes (such as hox gene mutations, though I'm unsure how drastic they were in the wild vs the lab) they tend not to. One of the sticking points the OP had was difficulty keeping in mind that mutations tend to be very minor and evolution happens across long time scales. Anecdotally I've found this a very common confusion amongst non-biologists.

Certainly, a mutation can result in huge changes, but it's a mistake to assume that there are genes that literally specify every aspect of an organism's body. There isn't a gene for "how many heads do you have", and a gene for "how long is your left pinky" and a gene for "what is the distance between your eyes" and separate genes for the locations of every hair on your head. Instead, a single gene (or sequence of DNA) typically modifies many different aspects of the organism.

 

[Ryan_m_b]

Yup, I am aware of that.