I will answer every question about evolution you have

My personal anatomy and physiology studies have me deeply Intrigued with a few evolutionary pathways...namely myofascial tissue and the evolutionary development at cellular levels. Just as an example question...how did sperm come to be the only cell with a flagellum? (In humans)
Or where and when fascial thixotrophy first became apparent...? What about the origin of muscle tissue...I know jellyfish were linked with an ancient type of muscle but where did that muscle tissue come from and how did it form?

A2D

originally posted by: Raggedyman

originally posted by: spygeek
a reply to: Raggedyman

He has answered you raggedy, but I'll have a go..

There are lots of advantages to sexual reproduction (giggidy), but how it originated is, like the origin of life itself, currently unknown with absolute certainty. It most likely first occurred in a single celled eukaryote. It may have orginated from a mechanism to exchange genetic material between cells, (bacteria do this kind of thing). A second possibility is that one cell ate another but incorparated some of its DNA into its own insted of digesting it all.

Why two sexes evolved basically is due to the advantages of having sexual reproduction. Asexual reproduction, wherein the fission of cells into identical daughter cells occurs, is how organisms such as bacteria and yeast reproduce. The issue with asexual reproduction is that over time (essentially hundreds or thousands of generations), bad mutations will build up in the genetic code, causing developmental problems. The evolutionary way to overcome this is to mix genes with another organism through "sexual reproducton" to produce offspring.

Mating types, (i.e. male and female), arose because they are advantageous mechanisms of reproduction. There is only one known group of organims that is truly 100% asexual, tiny aquatic organisms called bdelliod rotifer.

You ask how and why sexual organs evolved? Because they are evolutionarily advantageous. Having two separate organisms combine dna to reproduce will over time develop distinctive 'mating types'.

"Sexes" didn't appear suddenly, like you to seem to be saying with your last paragraph. Mommy and daddy weren't distinct genders in the early stages.

Thank you for that long winded yet irrelevant post

Did I ask what is the benefits of two parents? Anywhere?
I know the advantages of two parents, again that's not and has never been the question
Did I ask are they advantageous? Anywhere?
Please show me?

That is the why you asked about. Organisms reproducing by combining their cells with other organisms is why two "parents" came to be.

I asked why, not because it was advantageous but what caused this directional change, what made nature take a course it could never understand, as if by magic? Almost as if was guided?

The environment and genetic mutations over generations brought about the two sexes. What's so hard to understand about that? It's not magic. It's not guided. It's organisms adapting and evolving. Plain and simple. It isn't a sudden or instant process, like boom suddenly there are two sexes. The sexes diverged through natural selection.

I also want to know why an organism would could develop a receiving organ and another a producing organ and how they could decode each other's information

Slowly, over time, the organs develop. Bacteria transfer genes between each other using pilli, other organisms have different organs, each evolved according to the law of natural selection to fulfill the required role most effectively.

Any cell of any living organism is able to read the information in any dna molecule. Dna is a universal language of nature.

I don't want to know the why of what happens after two parentage, I want to know the why it became necessary and why it changed before it could produce offspring

As I said in my earlier reply, asexual reproduction produces a buildup of bad genetic mutations over generations, the first organisms to reproduce through sharing cells had an advantage and it is now the prevalent method of reproduction.

The answer lies in your simple statement "it's currently unknown"
So why have you and ghost added all that irrelevant fluff

We don't know precisely what organism first did it or what mechanism the process used, but we do know why it would have evolved and what it could have evolved from. Thanks is relevant and not fluff at all.

Why have you said you answered my question when you then say it's currently unknown

That's dishonest

Is their a solid scientific theory, something not based on faith?

We did answer your question. The theory of evolution is a solid theory. We know why the sexes evolved as they did and can pretty clearly theorise how. There is no faith required to understand science.

Thank you peter vlar and Spygeek, your explanations are very accurate and more than welcome.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
This again doesn't answer the question. You are not even paying attention to all the assumptions that you are making. You are assuming that an organism went from lacking all the necessary parts to produce sperm to having those parts and at the same time another organism would need to evolve the necessary parts to produce eggs.

I'm not making that assumption at all. To make that assumption would assume that these very complex mutations and organs occurred spontaneously. No where in evolution does this occur. Everything is an extremely gradual process that spans a population of a species over successive generations.

This basically is the same argument as "how can the eye, which is so complex, form all of a sudden when it requires [this and that] in order to function, but they can't function separately?" Again, this question is based on a false premise.

Just like we can see a transitional depiction with step by step evolution of the eye in living, modern organisms, we can also see the same transitional depiction with a step by step evolution of Sexual Reproduction from Asexual reproduction in living, modern organisms.

Here is the a biological tree that shows a proposed phylogenetic evolution of sexual reproduction in eukaryotic organisms.



Sexual reproduction doesn't require sexual organs identical to those found in humans (or other multicellular organisms in the animal kingdom). Just like the eye, the very earliest mutations of it are extremely primitive and not complex at all.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
You completely misread my question haha I am completely aware of all of that. The question I asked is where do new protein folds come from.

The quote you are responding to answers this question and details how new protein folds are formed.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
Proteins don't just fold into any shape. A relatively simple chain of amino acids folds into one specific shape out of the 10 to the 390th power possible shapes, and according to the estimate cited in the paper the maximum number of physical events in the universe is 10 to the the 150th power. Do you see the problem here?

I'm afraid I am not educated on the specifics enough to answer this question. Perhaps someone else here can

originally posted by: ServantOfTheLamb
a reply to: Ghost147
From EVOLUTIONARY BIOSCIENCE AS REGULATORY SYSTEMS BIOLOGY by Eric H. Davidson:
[Cut to save space for the rest of the post]

Thanks for the information, I agree that it is very interesting. It doesn't necessarily discredit Evolution, however, it simply suggests there's a mechanism that drives embryonic development of the body plan which the current model does not currently account for. Eric H. Davidson isn't showing that evolution does not exist, but simply that some of the ways we original describe how it functions aren't totally accurate.

I'll have to read more into discovery, again thanks for the information

originally posted by: BOTAL
a reply to: ServantOfTheLamb
Yes things evolve and adapt.
Indisputably.

But there must be some greater entity that started some basic lifeforms up.

It is definitely a possibility, and is actually one theory within Abiogenesis, but that does not necessarily mean that it's the only possible solution. Many other hypotheses within the topic of Abiogenesis have evidence to support the onset of life through natural means.

Of course, because it was so long ago, we only have evidence to suggest natural causes, and no way (at this moment in time) to form a theory that is beyond any reasonable doubt.

originally posted by: BOTAL
a reply to: ServantOfTheLamb
THE PROBLEM IS:
The series of changes in a row that build up to something that gives a reproductive advantage. When the first steps dont help until more are added
The first steps wouldn't stick so the chain of changes wouldnt be built.

This conundrum has been addressed in several posts on page 6.

originally posted by: BOTAL
a reply to: ServantOfTheLamb
THE OTHER PROBLEM IS:
Anything you would consider a chicken or egg situation.
Flowers are bright to attract bees.
Bees learn to like bright because it signifies a pollen rich flower.
Both traits evolved at once??????????
Because whichever came first wouldnt "stick" without the other.

This issue has also been addressed before in this topic, I believe it was on page 4 in response to Raggedyman's comment.

a reply to: Ghost147
You have addressed it enough to satisfy your own capacity of belief and acceptance

Sadly you havnt the capacity to understand that you haven't satisfied others enquirers


Bit like the religious that accept and defend their position, though not adequately for you

I am out

No answers forthcoming around this desert of knowledge

originally posted by: Raggedyman
a reply to: Ghost147
Sadly you havnt the capacity to understand that you haven't satisfied others enquirers

I can't explain an answer to your question if your question's foundation is based off of an inaccurate portrayal of the very theory you're asking about.

I, and others, can, and have, show you how your question is based on a false premise, however.

originally posted by: Raggedyman
a reply to: Ghost147
Bit like the religious that accept and defend their position, though not adequately for you

The fact that you don't even realize that your question is based off of attributes that do not exist in the theory you're attempting to question the validity of is mind-boggling. How many times do we have to show you that your question doesn't even pertain to evolution, it pertains to a misconception about evolution.

You have yet to actually ask anything about evolution at all because of the false premise in your question.

It's like if I asked you "Tell me why and how the son of god, Satan, came to Earth to save humanity and teach them to love god", and you respond with "It wasn't Satan, it was Jesus" and then I just say "You and your followers don't even understand the question I'm asking! Perhaps if I leave you to ponder it for a while, eventually you will grow some intellect and answer why satan came to earth to save humanity"

Do you see now what a false premise is?

a reply to: Ghost147

I'm not making that assumption at all. To make that assumption would assume that these very complex mutations and organs occurred spontaneously. No where in evolution does this occur. Everything is an extremely gradual process that spans a population of a species over successive generations.

Lets not misrepresent me. Maybe you did it to save space, but if you continue reading you will see that I said that would take a very long time. That is not an assumption I made there. The fact that it has to happen slowly doesn't help your case friend.

Just like we can see a transitional depiction with step by step evolution of the eye in living, modern organisms, we can also see the same transitional depiction with a step by step evolution of Sexual Reproduction from Asexual reproduction in living, modern organisms.

Here is the a biological tree that shows a proposed phylogenetic evolution of sexual reproduction in eukaryotic organisms.

I don't think we can see either of those things. I could go recreate that chart in two seconds. You aren't giving legitimate studies. You are giving renditions of what some Scientist claim happened without showing what information those renditions are based on they are worthless. I think you are assuming they have more information than they actually have.

Sexual reproduction doesn't require sexual organs identical to those found in humans (or other multicellular organisms in the animal kingdom). Just like the eye, the very earliest mutations of it are extremely primitive and not complex at all.

I never said they needed sexual organs identical to humans. Not just like the eye. I don't think you understand what is needed in order for a cell to become light sensitive. Many many things are needed. The fact that evolution doesn't happen rapidly is not good for you here. Natural selection does not work on a genetic level. It only works on what is expressed in the phenotype. So the process of getting a light sensitive cell is not as easy as you like to pretend it is. Again give me good sources and I won't have so much to say. Drawings of a five year old just don't cut it .

The quote you are responding to answers this question and details how new protein folds are formed.

You are still not understanding the question. Proteins are folded into three dimensional structures. This occurs after protein biosynthesis so protein biosynthesis cannot be the cause of new folds. From Wiki, "The events following biosynthesis include post-translational modification and PROTEIN FOLDING. " They are different processes.

I'm afraid I am not educated on the specifics enough to answer this question. Perhaps someone else here can

Rather have honesty over bull#

originally posted by: Astyanax
a reply to: Ghost147

Do art and religion have evolutionary benefits? And if not, what is your explanation for their universal or near-universal prevalence among human communities?

Eilasvaleleyn answered this quite well, actually. It's not that Art and religion are products of evolution, it's that a product of evolution.

Evolving God: A Provocative View on the Origins of Religion argues that the traits found in non-human species, such as chimpanzees and bonobos, traits that include high intelligence, a capacity for symbolic communication, a sense of social norms, realization of "self" and a concept of continuity, could be traits that could lead to both art and religion as a sort of byproduct from them.

There are theories that suggest Brain size, Tool use, Morality, and Communal living could also be factors that could contribute to these concepts/actions.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
Lets not misrepresent me. Maybe you did it to save space, but if you continue reading you will see that I said that would take a very long time. That is not an assumption I made there. The fact that it has to happen slowly doesn't help your case friend.

Ah yes, I didn't see that part. My mistake.

However, a 'slow' development does actually explain this. As explained further down in my post, Sexual Reproduction isn't simply based off of what we see in human anatomy. There are extremely primitive examples of sexual reproduction without the same organs, and a transition from Asexual to Sexual.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
I don't think we can see either of those things. I could go recreate that chart in two seconds. You aren't giving legitimate studies. You are giving renditions of what some Scientist claim happened without showing what information those renditions are based on they are worthless. I think you are assuming they have more information than they actually have.

You're absolutely correct. The hypotheses that revolve around Sexual Reproduction are highly speculative. No one is denying that. We simply do not have a direct way to study how it actually did arise. However, that does not mean we do not have evidence that suggests how it could have arose. And that is what the graph suggests.

Science does not claim to have absolute infallible answers to anything. It is simply a tool in which we use to describe how our observations of nature function using the information we have, and to the best of our abilities. There are no Absolutes in Science.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
I never said they needed sexual organs identical to humans. Not just like the eye. I don't think you understand what is needed in order for a cell to become light sensitive. Many many things are needed. The fact that evolution doesn't happen rapidly is not good for you here. Natural selection does not work on a genetic level. It only works on what is expressed in the phenotype. So the process of getting a light sensitive cell is not as easy as you like to pretend it is. Again give me good sources and I won't have so much to say.

The article you mentioned earlier challenges our current understanding of evolution, it does not debunk the phenomenon all together. Large changes do occur, and we have directly observed that, is this what you are denying? I'm not totally sure of your position.

Are you saying that Evolution does not occur at all, or do you mean to simply claim that our understanding of how it functions is inaccurate?

originally posted by: ServantOfTheLamb
a reply to: Ghost147
Drawings of a five year old just don't cut it .

These drawings are based on actual things and are drawn in a way so we can easily determine what is actually being expressed and depicted in what we have observed outside of those drawings. You seem like a very intelligent individual, so I don't know why you seem to resort to ridiculous comments like that.

originally posted by: ServantOfTheLamb
a reply to: Ghost147
You are still not understanding the question. Proteins are folded into three dimensional structures. This occurs after protein biosynthesis so protein biosynthesis cannot be the cause of new folds. From Wiki, "The events following biosynthesis include post-translational modification and PROTEIN FOLDING. " They are different processes.

Ah I see what you are asking now, when you said "What is the origin of a new protein fold", you meant how are new biomolecules created. As in a brand new structure. Is that correct?

originally posted by: ServantOfTheLamb
a reply to: Ghost147
Rather have honesty over bull#

I rather have civility over a presumptuous and pompous attitude.

Apparently that cannot be achieved by your side of the argument, as has been shown by a number of people in this thread that agree with you. What is the purpose of puffing up your chest in a debate and shouting "I am a winner, all you have said are lies".

Not only that, but why does everything have to be considered a lie? It's as if no one can simply be incorrect about something, it has to be 'bull#', 'lies', so on and so forth.

How about you act as a civil intellectual and we can continue without having to resort to harassment of the opposing position?

From my (limited) understanding, sex is likely to have originated from an early variant of phagocytosis (cells ingesting foreign objects/cells) resulting in cell-cell fusion and creation of hybrids. From then it would be a matter of natural selection, as introducing foreign genome is not always favorable I would think.

This would also answer the question of who was there first, mommy or daddy. Neither. Gender and reproductive organs is something that came much later.

a reply to: ServantOfTheLamb

Just an FYI. Sexual organs evolved around the ability to reproduce sexually, not the other way around. The idea that both sexes would have had to evolve all features simultaneously while not using sexual reproduction is a bit silly. In evolution that is not possible. Sexes predate most complex organisms, so it is obvious that it started with simple asexual organisms that developed the ability to reproduce BOTH ways.

a reply to: moebius

Yes, that is indeed one of the possible origins. There are actually a number different hypotheses we can form based off of the observations make in modern organisms

originally posted by: Raggedyman

originally posted by: BOTAL
a reply to: ServantOfTheLamb


Flowers are bright to attract bees.
Bees learn to like bright because it signifies a pollen rich flower.
Both traits evolved at once??????????
Because whichever came first wouldnt "stick" without the other.

How is it you can see my question yet others can't

Your inability to understand the information in front of you isn't tantamount to others not getting the question. I think that it's more likely that you don't actually understand what you're really asking.

A bee wouldn't survive without the color of the flower,

The color makes it easier to locate pollinating flowers but neither the pollen not the bees were initially dependent on the color of flowering plants. Flowering plants had an explosive period of growth that began at the same time as that of mammals 65 MA. Natural selection over that long period of time helped to select for bees that are
More reliant on color, sure. But that variety of clot didn't exist 100 MA when the first bees begin to appear in the fossil record.

the flower without the bee.

Then how exactly did flowering plants survive for a minimum of 40MA before bees split off from wasps?

The two must have evolved together, that's beyond chance

Why MUST they have evolved simultaneously? Because you're incredulous? Because you won't look it up on your own and
It makes you feel superior to play "gotcha" on a topic that my 8 year old is more knowledgable on? Well done! I don't have any evidence for the preceding sentences but they Must be true because...

It's like sexual organs, for some unknown and inexplainable reason nature decided that two parents are better than one so nature would provide codes, organs to develop in a singular moment by pure coincidence and random chance as if it was designed and Shazam male and female and offspring

Your refusal to either understand or accept that the origins of sexual reproduction predate gender differentiation is astounding. Have you never read anything on the topic that you are so up in arms about? You're on the Internet,
Why are you relying on other peoples answers on a message board instead of engaging in due diligence? Oh sweet irony...

Just a little to convenient for random chance to me

One without the other wouldn't stick logically

There doesn't seem to be much convenient about a process that has occurred for 100 MA with bees assisting and over 350 MA with pollinating plants doing just fine.

originally posted by: Ghost147

originally posted by: TheSorrow
a reply to: Ghost147

how is the genetic information that's added over time organized to eventually create a new species? I never grasped how nature is able to reorganize the info into something useful.

It's not so much that anything is organizing mutations as it is that if a mutation allows an organism a higher chance of surviving and reproducing, it gets passed down to it's offspring. The mechanism that allows for this is Natural selection.

I'll give my example of the moths from earlier, as it is a great example of natural selection.

Lets say we have a moth. It has a blotchy, spotted black color on it's white wings. It's environment is a forest, and within that forest are trees that have white and black bark. The moths rest on the trees, and their coloration prevents predators from spotting them easily.

The black spots vary in number from moth to moth, and some are so covered with these black spots that they tend to visually stick out when they are resting on the white trees. So, the population of the moths with more spots begins to dwindle.

That is Natural selection. And this incident im writing about has actually happened. Soon later, a factory was build next to the forest, and the pollution that the factory gave off covered the white trees with black soot.

Suddenly, the predators were then eating all the whiter moths, and the moths with more black on them began to raise in population.

So Natural selection weeds out disadvantageous mutations through environmental factors (in the moths case, the factor was predation). The more beneficial mutation prevails and has a chance of developing even further overtime, if that development would be an advantage in that environment.

This would be an example of Micro Evolution though, and you're wondering how we can progress far enough into another species (Macro evolution). Well, it's the same process, just accumulated over time. Here's another simplified form of looking at the similarities and differences between the two (microevolution and macroevolution)

If we were to take one species, and separate the population, placing the -now- two populations in different environments, mutations would occur to each of the populations over the generations that would allow those organisms to adapt to the different environments around them. This would be an example of Microevolution. Given enough time through successive generations, both of the populations (even though they were the same species to begin with) would accumulate different mutations and eventually their genes would drift so far from each other that the two populations would not be able to breed anymore. That’s one indicator that they’ve become a new species.

Let’s say we pretend a second in time, is equivalent to a mutation. As time goes on, more seconds are added. Just like in our first example when the two populations accumulated mutations. Eventually we gather so many seconds that we can define new term in time, 1 minute. Using our example from before, there were so many accumulated mutations that we could define an entirely new species. Just like a bunch of seconds can create a minute, a bunch of mutations can create a new species.

If we continue this process, more seconds are added and new minutes occur, eventually we have so many seconds that we can make a new definition, an hour. We could view the same thing in taxonomy, where an hour would be similar to a genus. We could go further to say that a day is a family, a week is an order, so on and so on.

They all came to be from the same process of accumulation, just viewed at a larger time scale.

This is a great response to why, but not how. I appreciate you taking the time. But there has to be a means for nature to take the info that is passed down and organize into something useful.

originally posted by: TheSorrow

originally posted by: Ghost147

originally posted by: TheSorrow
a reply to: Ghost147

how is the genetic information that's added over time organized to eventually create a new species? I never grasped how nature is able to reorganize the info into something useful.

It's not so much that anything is organizing mutations as it is that if a mutation allows an organism a higher chance of surviving and reproducing, it gets passed down to it's offspring. The mechanism that allows for this is Natural selection.

I'll give my example of the moths from earlier, as it is a great example of natural selection.

Lets say we have a moth. It has a blotchy, spotted black color on it's white wings. It's environment is a forest, and within that forest are trees that have white and black bark. The moths rest on the trees, and their coloration prevents predators from spotting them easily.

The black spots vary in number from moth to moth, and some are so covered with these black spots that they tend to visually stick out when they are resting on the white trees. So, the population of the moths with more spots begins to dwindle.

That is Natural selection. And this incident im writing about has actually happened. Soon later, a factory was build next to the forest, and the pollution that the factory gave off covered the white trees with black soot.

Suddenly, the predators were then eating all the whiter moths, and the moths with more black on them began to raise in population.

So Natural selection weeds out disadvantageous mutations through environmental factors (in the moths case, the factor was predation). The more beneficial mutation prevails and has a chance of developing even further overtime, if that development would be an advantage in that environment.

This would be an example of Micro Evolution though, and you're wondering how we can progress far enough into another species (Macro evolution). Well, it's the same process, just accumulated over time. Here's another simplified form of looking at the similarities and differences between the two (microevolution and macroevolution)

If we were to take one species, and separate the population, placing the -now- two populations in different environments, mutations would occur to each of the populations over the generations that would allow those organisms to adapt to the different environments around them. This would be an example of Microevolution. Given enough time through successive generations, both of the populations (even though they were the same species to begin with) would accumulate different mutations and eventually their genes would drift so far from each other that the two populations would not be able to breed anymore. That’s one indicator that they’ve become a new species.

Let’s say we pretend a second in time, is equivalent to a mutation. As time goes on, more seconds are added. Just like in our first example when the two populations accumulated mutations. Eventually we gather so many seconds that we can define new term in time, 1 minute. Using our example from before, there were so many accumulated mutations that we could define an entirely new species. Just like a bunch of seconds can create a minute, a bunch of mutations can create a new species.

If we continue this process, more seconds are added and new minutes occur, eventually we have so many seconds that we can make a new definition, an hour. We could view the same thing in taxonomy, where an hour would be similar to a genus. We could go further to say that a day is a family, a week is an order, so on and so on.

They all came to be from the same process of accumulation, just viewed at a larger time scale.

This is a great response to why, but not how. I appreciate you taking the time. But there has to be a means for nature to take the info that is passed down and organize into something useful.

Isn't this adaptation anyways? Not evolution?

I know some would suggest that adaptation is evolution. But then how would you jump from one species to the next? The information must be organized somehow... Right?

Can humans from every corner of the earth reproduce with each other? Why?

It seems that over millions of years, even small variations in temperatures, altitude, availability of different foods, etc, would cause us to be quite different, even creating different species?

I guess I don't understand how we can have 7 billion people that are more or less the same, aka able to procreate.

Does evolution know what's going on, on the other side of the world?

Is evolution more predictable than we seem to assert?

originally posted by: Ghost147

originally posted by: ServantOfTheLamb
a reply to: Ghost147
Rather have honesty over bull#

I rather have civility over a presumptuous and pompous attitude.

Apparently that cannot be achieved by your side of the argument, as has been shown by a number of people in this thread that agree with you. What is the purpose of puffing up your chest in a debate and shouting "I am a winner, all you have said are lies".

Not only that, but why does everything have to be considered a lie? It's as if no one can simply be incorrect about something, it has to be 'bull#', 'lies', so on and so forth.

How about you act as a civil intellectual and we can continue without having to resort to harassment of the opposing position?

I'm starting to think that particular individual is a troll. There is a common theme of accusations of not reading its posts correctly, refuting clear explanations by saying the question was not addressed and just repeating the same inaccuracies, resorting to an antagonistic/defensive position..

"How did X happen?"

"X happened because a, b, and c."

"I'm not talking about a, b, and c! I want to know how X happened."

a reply to: peter vlar

Then how exactly did flowering plants survive for a minimum of 40MA before bees split off from wasps?

God.

Why MUST they have evolved simultaneously?

God.

For all questions - God is the answer.

a reply to: deadlyhope

A big part of the reason that every living person is still closely related enough that we can still mate is a genetic bottleneck event that occurred 70KA. This even nearly eliminated all of humanity and reduced worldwide populations of Homo sapiens Sapiens to less than 1000 breeding pair and perhaps as few as 100. Populations of Neanderthal and H. Altaiensis already had dwindling populations and as a result many populations of our cousins suffered from inbreeding related deleterious mutations.this bottleneck event was the beginning of the end for a them. Now keep in mind that the last common ancestor of Us, Neanderthal and Denisovan was H. Heidelbergensis and the gap seperate get all of us from HH is roughly 600 KA. In the grand scheme of things, that's not very long in geological time and we were still able to hybridize with each other. The different temperature, environment, food etc. which you allude to is a pretty recent phenomena occurring in the last 60-80 KA that HSS has left East Africa to explore the rest of the globe.