Just an assorted collection of some of the ideas I have been reflecting on in the past year or so :
1. The deep, powerful revulsion of the Neanderthal has overtones of profoundly ingrained biological reflexes designed to preserve life, like the fear we see upon suddenly discovering a snake, a spider or a festering wound. I am convinced that the immensely strong immune systems of the Neanderthals enabled them to harbor any number of deadly, virulent and lethal strains of staph that rendered any contact with them in the form of a bite or scratch to be a death sentence. These micro-organisms were harmless to them amongst themselves but would rage through strangers like wildfire, killing them as quickly as flesh-eating bacteria do today. When part of this immune system was transferred to Europeans, it made them into living bioweapons that eliminated whole races of men by simply arriving at their shores. The strong fear and loathing of the Neanderthal persists to this day - the sight of the round eye and retreating periorbital socket triggers ancient instincts in certain breeds of men to retreat. In the schoolyard this subliminal feeling of fear is coped with by bullying children who resemble or remind others of Neanderthals. This wise strategy of a wide berth led to the victorious practice of attacking them from a distance with projectile weapons and never allowing them to approach for close quarters combat.
2. The combined hybrid of Neanderthal and Sapiens led to a creature which survives best on a low carbohydrate protein diet in most cases, but the intestinal tract has retained the practice of requiring roughage to stimulate it to elimination. This has left the digestive design of mankind a very weird affair with great difficulty in getting both proper nutrition and proper stimulation of the bowels and critical inner lining of the intestines necessary to absorb nutrients.
3. The inheritance of the paranoid, worrying anxiety about the future has been one of the strongest and most successful of the traits transferred from Neanderthals to Europeans. It leads to perpetual states of overkill where Europeans feel the need to prepare many strategies and accommodate many possible courses of action and were formerly highly unlikely to ever be caught too far afield by the unexpected. This trait of constantly projecting scenarios into the future and trying to prepare for anything both at the individual and the group level has formerly made them nigh indestructible similar to their Neanderthal ancestors. With the loss of these traits and social engineering designed to suppress these instincts in the modern era, the European has essentially surrendered the genetic trump card in his makeup. If he simply waits for the future to arrive and hopes everything will be okay he is throwing in the towel to return to his animal roots, losing nearly all the advantages conferred upon him in the past by this kind of waking dreaming.
4. The locomotive systems of the two species has favored the original design of Homo Sapiens, sacrificing power for endurance for long distance trekking. The Neanderthals powerful waistless frame was intended for a homebody who rarely ventured more than a couple hundred kilometers on foot in any direction. The transfer of some of the muscle mass and shape from Neanderthal to Homo Sapiens has likely reduced their capacity for long distance endurance slightly while increasing their upper and lower body strength significantly over other races. The Kenyan super distance athletes are probably fairly representative of the bodies of Sapiens before the hybridization. Kenyans are notoriously weak people who can otherwise run or walk any other race into the ground and they have substantial advantage in energy management. It is blindingly obvious that the Neanderthal's dietary requirements meant he would have to carry huge amounts of meat with him if he intended to go very far from home, sort of like an oil tanker that would require the gas tank hooked up to it's own reservoir to keep the engine running for very long. This critical aspect would have contributed significantly to the Sapiens ability to wander for years over huge distances surviving on carbohydrates derived from plants he harvested along the way.
5. The Melonheads likely were wiry and quite strong compared with their slaves for this reason, possibly used to being transported by slaves atop carriages with little need on their part to walk long distances. They would have been less strong than Neanderthals but would have preferred their slaves to have little upper body strength that would threaten them. It is also likely from both the fossil evidence and the mythical lore that they towered in height over both of the other two species of man. I envision them as averaging around seven foot (a frequent height found for melonhead skeletons) with some of them running nine feet or higher. They almost certainly contributed to the legends of giant rulers and colossus tyrants who are found throughout oral and written traditions. I also believe it was common for them to display red hair, double rows of teeth and extremely piercing eyes. They probably contributed to the perception of their great size by wearing hats and crowns designed to emphasize their lofty perspective. I see their locomotion as emphasizing their status and not being constrained by efficiency, a sort of ponderous, leisurely gait where they appeared to be virtually sliding wherever they went, without any need to practice any kind of economy other than elegance and regal independence. Highly unlikely that anyone with Neanderthal or Melonhead ancestry would ever win any medals in the marathon at the Olympiad.
Hope you find these ideas interesting. I may put some more of them up here in time just to hear what others think on this subject.