Doma, I am afraid you have kind of lost me with this:
"Why did the massively physically weaker and
12hr a day hunter evolve from a massively stronger 24hr a day hunter....?"
which seems to be the cornerstone of your comments in this post.
H. erectus, which is what the consensus believes we are to have evolved from is believed to have been largely between 4'-9" and 6'-1", on average a little smaller than us. Similarly weight estimates are in the range of 88-150#, again, smaller than us.
Both we AND neanderthal are believed to have evolved from that. Neaderthal was certainly a more robust creature, with a huge brain (bigger than ours) and all sorts of eye socket fun, etc.
But, critically, we do not come from them and they did not come from us. We are not in their line,they are not in our line. We have a common ancestor, yes, but we did not get here through them and they did not get where they went through us.
We did not evolve from the massive Neanderthal, we evolved from the more slight Erectus (as did they).
A component of now outdated thinking is that human evolution was along a single line of changes. It is now more accepted that there was significant radiation and that as many as a half a dozen Homo spp. were wandering around at the *same time* all with a common earlier ancestor. One of these variants is the one that made it to today, but they are not all co-linear, they are collection of branches most of which failed.
For decades human evolution was explained in co-linear terms, the notion is now considered bunk.
SO, the question is not "how did we come from that" because we didn't, the question is "why did we survive and they not"
On that:
"Evolutionary biologists have long recognized the role serendipity plays in which species thrive and which wither on the Darwinian vine. Without the asteroid impact 65 million years ago, for instance, mammals would not have spread so soon into almost every ecological niche on Earth (dinosaurs were in the way). Yet when the subject strikes as close to home as why our ancestors survived and Neanderthals did not, scientists have resisted giving chance a starring role, preferring to credit the superiority of ancient H. sapiens. Both are descendants of Homo erectus: some spread across Eurasia beginning 1.8 million years ago and evolved into Neanderthal by 300,000 years ago, and others evolved in Africa, becoming anatomically modern by 200,000 years ago and reaching Europe some 45,000 years ago.
These arrivistes are often portrayed as technologically and culturally more advanced, with their bone and ivory (not just stone) tools and weapons, their jewelry making and cave painting—the last two evidence of symbolic thought. Finlayson has his doubts. Neanderthals may have painted, too (but on perishable surfaces); they were no slouches as toolmakers; and studies of their DNA show they had the same genes for speech that we do. "They survived for nearly 300,000 years," Finlayson says by phone from Gibraltar, where he is director of the Gibraltar Museum. "That modern humans got to Australia before they penetrated Europe suggests that Neanderthals held them off for millennia. That suggests they weren't that backward."
Instead, moderns were very, very lucky—so lucky that Finlayson calls what happened "survival of the weakest." About 30,000 years ago, the vast forests of Eurasia began to retreat, leaving treeless steppes and tundra and forcing forest animals to disperse over vast distances. Because they evolved in the warm climate of Africa before spreading into Europe, modern humans had a body like marathon runners, adapted to track prey over such distances. But Neanderthals were built like wrestlers. That was great for ambush hunting, which they practiced in the once ubiquitous forests, but a handicap on the steppes, where endurance mattered more. This is the luck part: the open, African type of terrain in which modern humans evolved their less-muscled, more-slender body type "subsequently expanded so greatly" in Europe, writes Finlayson. And that was "pure chance."
Because Neanderthals were not adept at tracking herds on the tundra, they had to retreat with the receding woodlands. They made their last stand where pockets of woodland survived, including in a cave in the Rock of Gibraltar. There, Finlayson and colleagues discovered in 2005, Neanderthals held on at least 2,000 years later than anywhere else before going extinct, victims of bad luck more than any evolutionary failings, let alone any inherent superiority of their successors."
http://www.thedailybeast.com/newsweek/2009/10/28/survival-of-the-weakest.html
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