2. Does human instinct always predominate?

Firstly, newborn humans cannot survive without being taken care of, so there may be a fault in your starting premise.

Ok, given that they are not newborn but at an age that they can fend for themselves, it's still not certain by any means that they would be able to find food and water or build a shelter. If they did manage to do any of these, it would be by sheer luck. The highest chances are that they would be malnourished and die from either malnourishment or diseases due to underdeveloped immune systems.

If they did manage to survive until puberty and are somehow healthy, then lack of parental love and supervision, and lack of contact wiht other humans or a society would likely make then more violent than normal humans towards each other, which would manifest as actual physical violence from the boy towards the girl and withholding of resources from the girl towards the boy (each fighting with what natural weapons they have). Again, this is assuming that there is no moderating material in their genetics. If they are high-IQ individuals, then they could even be compassionate towards each other... because compassion is a function of IQ.

If they reach puberty, their basic instincts would definitely take over and sex would happen ultimately, firstly as a simple exploration of the differences of each other's post-pubescent bodies, and then actual sex as they get to know their own and the other's bodies. Arousal would happen during the simple exploratory phase, which would be instantly visible in the boy. This would intrigue both and further exploration would ensue. When periods start for the girl, this would further heighten the intrigue for both, and lead to more exploration. All this would ultimately lead to sex, as this is a natural instinct that does not need to be taught.

If sex happens and they are healthy, then they would procreate. And if the girl delivered a baby successfully and survived, then that's where love would begin... as another natural and basic instinct of loving your offspring would take over. This is the beginning of love and through the love for their offspring, the two individuals would start developing love for each other.

However, the entire scenario is highly unlikely, because if two humans that are so young are thus deserted, they would not survive.

This sounds like a classic discussion question from the late 19th century; men in their clubs reading the news, smoking cigars / pipes, drinking, dining/having tea, and discussing matters of both real and speculative natures...

Assuming that your givens result in them getting to puberty, I think the sex drive and curiosity could easily create a situation where they would discover copulation, and eventually get the girl pregnant.

I would classify that as a broad instinct across most any species, not confined only to humans.

[Whether or not the birth is successful is a different matter.]

[sep]

An important aspect of note in the "Nature v. nurture" discussions is that the rôle of the individual's own determination / drive is typically ignored, in spite of being a really important third element (moldable by both Nature and nurture), a non-trivial oversight.

Look at what happens in nature around us...

You have two lions bred in captivity and kept in zoos. They are put together and... Lion cubs.

There must be some basic procreative force. We humans with our "intelligence" have so screwed ourselves up over it and love and society etc we've forgotten it.

But in your hypothetical example I feel that yes that they would mate.

They would, I think, at an early age become partners/friends/companions and as time went on, their natural instincts would prevail. I don't think they would necessarily fall in love (the classic love), but I do think they would bond and raise children free from any taboos society puts on us.

So Brother and Sister or completely unrelated? The answer may well determine expected outcomes.

It's an entirely implausible scenario but yeah. Their behavior would be entirely instinctual. Just like every animal. Because humans are animals.

See various societies like the Click Language of the San Bushmen People:

[media=https://m.youtube.com/watch?v=c246fZ-7z1w]

See on YouTube if this is private:

m.youtube.com/watch?v=c246fZ-7z1w

Or the Zo' é tribe of Brazil

[media=https://m.youtube.com/watch?v=zYutcG14C7c]

https://pib.socioambiental.org/en/Povo:Zo'%c3%a9

In addition to the Link I gave on blue lagoon.

Sociologist take it from the neanderthal point of view.

Neither of the above never had neanderthal DNA! We do!

And here is some DNA evidence about some of the people in South America. Australia of all places...

https://www.science.org/content/article/ancient-dna-confirms-native-americans-deep-roots-north-and-south-america

Pretty much the same thing has happened in the animal world so yes they would without any education couple.

Check literature on The Westermarck effect, also known as reverse sexual imprinting. It is a psychological hypothesis that states that people tend not to be attracted to peers with whom they lived like siblings before the age of six. This hypothesis was first proposed by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one explanation for the incest taboo.

They will probably see animals mate. That's enough to give them a clue.

Apparently. Some people responding cannot deal with the hypothetical.
Interesting. They would probably develope some form of communication. I believe there would be some attraction.
Definitely lots of experimenting and exploring

Stephie, that is a truly fascinating conundrum (for lack of a better word) you posted circa 6 weeks ago. 👏 Quite detailed as well. My quick thought is also that instinct would be predominant. Hopefully, you will publish more like this in the future.

Being “civilized” came from people discovering less need for instinct within developed societies. So I imagine those kids would be very instinctual initially, but if they developed far enough, they would have less need of those instincts.

They will develop their own language and will be able to communicate with only each other. Men and women have procreated hundreds of centuries before sex education and visual aids, they will probably be OK

Probably, innate behaviour. Have you ever seen the movie "Blue Lagoon", Stephie?

I'm guessing they would figure things out and, like most humans, seek each other's company.

I'm pretty sure that nature would take its course....

Ur right stephie they would be able to

I think instinct would dominate there, yeah.
I wonder if they'd be able to speak to each other though, since they didn't acquire a first language as children.

You know, it's interesting that you ask this. I thought I read somewhere about a Nazi experiment, the records of which I cannot currently locate. Allegedly, according to my memory of what I thought I read, they took a group of children from their parents at the earliest possible age they could without them dying of loneliness, then raised them in a room with nothing but each other for company. All their needs were met. There were enough beds for all of them, there was always enough food provided, albeit without any human contact other than each other. They did not want for anything, and so you would think they would be content and happy. But according to what I read, they became violent. The experiment ended when one of the children killed another.

As a behavioral specialist I can say that NO, basic instinct would NOT predominate and NO, they could NOT find love for each other and finally, yes, they would intuitively know how to procreate as two human beings but NO, they would NOT feel naturally inclined to procreate with each other. Keep in mind that humans have intuition, not instinct. Only animals have instinct, but animals do not have intuition.

The reason the answers above are "NO" is because of the boy/girl biological connection with each other as biological siblings. The biological connection we have with siblings and bio-parents is Nature's way of diverting us away from acts of incest.

That is why girls hate their biological brothers and why girls suddenly begin to hate their biological father as the girl approaches puberty.

IF on the other hand the brother and sister were adopted within the family or at least one of them was adopted, then all of my "NO" answers above would immediately turn to "YES".

If a girl was adopted into a family and her Dad was not her biological father, she would NOT feel naturally repelled at the sight of her adoptive Dad as she approached the age of puberty and therefore, would not feel naturally repelled from any sexual advances he might make toward her.

This occurs because of the absence of that natural, biological connection between the two of them which otherwise would be Nature's deterrent for incest to occur between father and his otherwise biological daughter.

A biological father to a daughter feels a natural sexual repulsion involving his biological daughter, but would NOT feel a natural sexual repulsion to a non-biological girl who was the same age as his biological daughter.