The first fratricide hinted at in Genesis:
Vestige of the tragic younger brother cro-magnon who kills older-brother Neanderthal
In the beginning, God designs the universe to eventually produce a human (with various other not-quite-human species emerging on the way). Think of the first genetic mutation human, alone, who has no parents since they are genetically very different than him. Maybe they cast him out, and he sees no others like him, and then he's trying to find a mate, but there isn't any. He mates with the others but considers them to be like "chayat hasadeh"! and then finally God finds him one that is genetically like him ("etzem me'atzami", etc). Maybe it is one of his children from his matings with the earlier species he was born from (as stated in Genesis, God brought to him all the creatures to find him a mate), This mate is a female who is genetically human as he is [Note: even in the Eden story, it is clear that Adam/Eve's children mated with each other, so this is not an issue when there is literally no-one else, (as perhaps Lot's daughters thought after the destruction of S'dom)
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Humans were more intelligent than their close cousins the Neanderthals and perhaps other near-human species, had a larger brain(/body ratio) than they did, walked more erect than some, certainly than their evolutionary ancestors, and eventually discovered agriculture. All this is reflected in the accounts which God dictated word by word to Moses:
1. Think of the Eden story as being written by a prophet after some changes had occurred to human society: "le'ovdo uleshomro" means they had (discovered agriculture and some) became farmers (and of course kayin/hevel represent the hunter-gather/farmer split).
2. Upright walking was already old, but it remained in some sort of memory, and the issue of upright vs non-upright is mirrored in the transition-in-reverse as a punishment for the snake.
3. Eating from the Tree of Knowledge means becoming more intelligent than their forebears.
4. There was a new situation for women re childbirth: children now had a larger brain, and the birth was from a body geared for upright walking and therefore smaller pelvis, and a diet based on carbohyrates rather than animal proteins and therefore with new energy constraints - with all three leading to more dangerous and painful childbirth.
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Humans were able to speak, and indeed the power of speech is considered the mark of humanity, and some commentators consider that to be the meaning of "in the image of God". But could Neanderthal (or other prior species) speak? Did they converse with humans?
Who does the snake represent? The snake is a being who could walk on two legs but then devolved into a non-walker. Or was denigrated by humans as one?
Can the snake symbolize an earlier and jealous species, why is the snake pushing us to eat of the tree - won't this make us smarter and therefore more dangerous to them become smart? Maybe it was a way to get God to kill us off? And the snake is pictured as very sly, and probably had eaten from the tree....so maybe Neanderthal was there before we came on the scene, and was jealous that we went beyond him, as is the case in Genesis with all older/younger pairs, but in this case we the younger usurper killed our older brother.
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Kayin who works with animals though not a hunter, kills the farmer brother...maybe the rest of Genesis-history we need to work that off by having it happen in reverse, the wars of the older-younger? (And of course Esav is a hunter..)
Maybe there was competition/war between older species like Neanderthal etc, and even non-fully-erect species, and they hated the smart erect farmers, and cursed them, and all this is remembered in various ways, by our taunt that considered them not erect but crawling, and the reverse taunt that for farmers the earth will give forth "kotz vedardar", which never was a problem for hunters, only for farmers.
And maybe snakes and scorpions etc which bit ("hu yeshufcha rosh...") was a problem for all, but the new-fangled smart types started to wear shoes and the curse of the others was that it wouldn't help: "Oh yeah, you uprights consider us hunched people as belly-crawlers, ok, so we'll bite you..."
All this is somewhat fanciful and not yet thought-out.
We know that even the greatest prophets after the time of Moses could not perceive clearly that which God presented to them in a prophecy, and from "makel shak'ed ani ro'eh...tov ra'isa" we can glean that what they did perceive could have been some sort of allegory. And if the story was composed based on Traditions available to human society thousands of years after the prior species was eliminated, and very long after humanity emerged, it cannot be expected to be historically accurate, nor was it meant to be - it is a very deep and precious record, which was seen by God as sufficiently deep and holy as to be included in what was divinely revealed to Moses in word-to-word transmission from God.
It may be that more thought, and more research in genetics and paleontology etc, will help us more closely identify actual historical aspects reflected in the Biblical accounts.
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Question for researchers: Would a Neanderthal child born to a human-Neanderthal couple where the mother was human, lead to death of the mother in childbirth because of the skull size? Or maybe the reverse is true if energy is a consideration since maybe human brains consume more energy even in the womb?
Maybe if the father is human then the larger pelvis of the Neanderthal mother and her greater feeding capacity could enable her to give birth to a human brain and the pelvis would easily accommodate the head-size.
But if the mother dies would the child die if he was stuck inside or would they cut her open to get the child? maybe humans would do that but not neanderthals (maybe they were not smart enough, or not ruthless enough?)
See: http://www.bbc.com/earth/story/20161221-the-real-reasons-why-childbirth-is-so-painful-and-dangerous
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