How did Altarians come into existance

No, they weren't. The Dread Lords later manipulated some of the Altarians, but they didn't create them. The Altarians came into existence due to the presence of the Dark Mithrilar on Altaria.

If you really want to know more about them, just start a game as the Altarians in GalCiv 2: TotA, and read the descriptions of their techs. Especially A History of Benevolence tells you a lot about them.

I mentioned this many times. Others have as well. I'm a bit worried that people are not bothering to read these things. (Sigh) It goes something like this (I'm working from memory by the way):

Long ago, the Dark Mithrilar arrived in the galaxy. That person was a human (not a normal human) and arrived through unexpected means. According to what I've read, he is a human from another dimension where the humans there are advanced enough in technology that they are able to bestow additional amounts of dark energy on to people. If you haven't caught on yet, in the fiction that Brad writes, Dark Energy = soul & magical powers. His arrival (possibly through time travel) had such an effect on the local dark energy of the new universe that it caused humanity to be the template that all intelligent species would become like. That is why so many creatures in the GalCiv series are humaniod (and why it would be bizarre if intelligent life would take any different form).

Anyways, 2 of the first species that came to be (I forget some details) were collectively called (at the time) the Arnor. They essentially had first dips on the dark energy and were immensely powerful for it (a single one of them could do more than a million humans). The species that retained the name of Arnor were human like, but couldn't perceive time. They could in theory sit down and watch the land change, glaciers form and melt, without the concern for the passage of time or the sense of boredom. The faction that would become known as the Dread Lords however could sense such things. In fact, they were the first to realize that the time the universe would last was finite, and decided that it was a moral imperative to make optimal use of this time. Since they were the most potent of species (along with the Arnor), they made a form of utilitarian calculus decision and decided that they should destroy the lesser species since they couldn't possibly use the space and dark energy they had as well as themselves (sharing was not an optimal use of this time). The Arnor objected and eventually the precursors wars started.

At some point during the war, the Dark Mithrilar landed on the planet that would become Altaria. He had a such potent effect on the local dark energy that some of the local life began spontaneously taking on human like qualities until they were essentially human (but with more dark energy). He had told them that their brothers, the humans, would eventually come to be through natural means (he being a dimension hopper, probably knew that he was in the neighborhood of dimensions where humans do evolve).

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So yeah, that is the quick version. I'm working from memory, and Brad might be retconing things, so I'm unsure the accuracy on some things. I don't have links off hand for the things I've mentioned (and some of the information might actually be in the games instead of the net).

I'll go looking, but I'm sure other people already have the links sorted for people whenever these frequently asked questions come up. In fact, in the time I wrote this reply, someone might have already posted some of those links.

Edit: Some spell checking and comments. Yes, go play GalCiv 2: Twilight and play as the Altarians. Reading the tech descriptions of their techs should give you many insights.

Go read the stuff in the GalCiv 3 databanks. It should be more accurate than anything I have to say on this topic. It would be near the top of the GalCiv 3 page.

Here if you can't find it:
https://www.galciv3.com/databanks

The timeline has a good chunk of the information I already posted about:
https://www.galciv3.com/databanks/timeline

It was the Databanks and the timeline that brought up the question. You answered one part of the equation that no one seemed to explain. Humans evolved on earth and time traveled. Also came from another dimension. These dimensions that everyone come from are like sliders. Through a process of war some ended up on Altar or Altaria. This was more of an accident that the Altarians picked up the Dread lords Dna, but of a matter of fact this caused everyone to be humanoid because of inter dimensional time travelors. I remember from a mega event that someone gets a crystal that enhances them. The Arnor was vreated by this crystal.

*Scratches head

Umm... I believe it is just the one human, not a civilization of humans who came to the Galactic Civilizations dimension. From the stuff I've read, there was never any hint that there was anyone else who came with him. For all we know, his civilization might be extinct, or he has traveled so far from it (through the dimensions) that he probably wouldn't be able to return even if he wanted to (nor would anyone be able to find him).

I'm not sure what you mean by sliders. In the stories that Brad writes, he includes stuff like when multiple outcomes exist for a possibility, the dimension in question splits so that each possibility gets to play out. Of course these new dimensions will also split when multiple outcomes presents itself, so the total number of dimensions grows very fast.

If I recall correctly, this dimension traveling time traveler got rather nihilistic after a while because for each event he could choose to do good, there would be another one where he didn't. Likewise, for each event he chooses to do good, there would be an outcome where he would succeed, but another where he would fail. Plus there is a great many dimensions that needs saving, but he couldn't possibly choose to save them all. He could choose to save only one at the time (more new dimension for each pick), or choose to do nothing. The stress got to him and much of the rest of the story I refer to follows how he got out of the nihilist mess.

Ok I guess you don't realize that you are describing the story concept on the show sliders if he couldn't go home. The show works off paralel world concept. You are describing the paralel world concept that I've seen everyone use recently except Dungeons and dragons. They are obviously not using dimensions they use in mathematics and D and d. Yes if  they were stranded in another world after their first slide  they would have it except there also was some time traveling involved. If you don't see it that way than I can't help you. I didn't realize that I said more than one. I do realize that this is not the Arnnor, but the Milithar. Thanks for clarifying now I can stop thinking of this, and now move on to something else, but I would be happy to keep discussing this. you could start by telling what the whole show concept was about. Though I'm pretty sure it was about paralel worlds just like the ones you describe, The term dimension used in the game is more like the way everyone talks about paralel worlds except D and d.

It is just one former human, the mithrilar Draginol. And the Altarians do not have human DNA, they simply resemble humans quite closely.

Sliders was an old TV series in which the characters were sliding through various alternate universes. 

The crystal was the Telenanth, which was used to create the Arnor (the more powerful Dread Lords and the weaker but more numerous Arnor). 

The Telenanth was shattered in a struggle among the five Mithrilar, that left only Mascrinthus and Draginol. I think this same struggle is what allegedly changed physics to enable life to evolve. Fragments of the Telenanth were taken to Altar to harness the dark energy seeping from Draginol. These are shards in Elemental/Fallen Enchantress/Legendary Heroes. Other shards of the Telenanth are part of the transcendence victory condition in GalCiv 2.

Yeo more than happily satisfied now about my question.