The Space Jockey,like the creature that has come to be called the 'Alien',is a bio-gentically engineered life-form. Built and programmed for a specific purpose,in this case,to pilot the biomechanical,'living' craft it is apart of.Nothing more and nothing less.
The creature is fused simbiotically into the acceleration couch and drive apperatus it pilots the ship with.Its a singular entity or no, the ship was not populated by Space Jockeys. Firstly it has no neck or backbone.Its back is intergrated into the couch it reclines into.The original inhabitants of the ship or those that engineered the Space Jockey,the ship it pilots and the Alien bio-weapon,can be seen in the painting by HR Giger entitled 'Alien Heiroglyphs'. It depicts two roughly man size creatures,one being attacked by a face hugger. The painting is a general depiction of the Alien life cycle. It was to be seen on the walls of the derelict,but was pulled at the last moment. A shame,as it would have saved much confusion over the years.
There is also a scene,it too pulled at the last moment of the three Nostromo astronauts venturing toward the craft and stopping for a rest halfway. Ash,monitoring their progress from his observation blister,notices,but fails to mention to the crewmembers,the appearance of what looks like the fossilized remains of a roughly six ft creature in the rocks behind where the astronauts sit.
Or one of the many crew members who tried to flee the holocaust unfolding on the derelict,and died in the inhospitable conditions of LV-426 atmosphere.The picture can be seen in the original Topps Bubblegum Alien cards circa 1979.
Designed by HR Giger,anyone who understands the concept of Gigers art should have no trouble with the original concept of the Space Jockey.Obviously benign in nature. It put out an interstellar warning for all ships to stay away. A conscious act of
Secondly,at 18ft in height,had it been able to stand,it would be kicking the Aliens around like footballs as the Aliens tried to kneecap the Space Jockeys with their inner jaws. An Alien(s) would have a heck of a time dragging 18ft creatures into
the hold to morph them into eggs as the original and much destroyed canon dictated.That would also make for one rather large egg. Not to mention the spatial circumferance needed to fill the hold with such a large lifeform. The eggs were clearly seen spaced closely together. Its all common sense though really.
Neither Ash nor Mother/MUTHR,the ships onboard computer could identify the derelict.Either a long extinct species or one from as yet,uncharted space. The concept of introducing somthing as comic book as the Predator with the hard core sci-fi element of the Space Jockey and its benign creators is nothing short of ridiculous to say the least.Fan boy guff and spotty stupidity.
To sum up,the Space Jockey and Alien are both biomechanical constructs. This alone should indicate they are of the same origin.The probability of having two seperate biomechanoid species evolving on diffrent worlds,then by chance bumping into each other is 100 trillion to one if at all. It would be like humans encountering humans living on another world in the far reaches of space. Pretty much a non event.
Like 'Mother' on the Nostromo the Space Jockey is a more highly advanced version of the same idea,albiet of an alien mindset,asthetic and understanding. Its transmission(s) (heard in the restored versions of the film),are truly bizzare and altogether freaky. There are two versions to heard,both as strange as the other.
A pilot,who other than its ability to rotate on a giant turntable,is fixed into position and is engineered to pilot and navigate the depths of space.Its immobility made it a soft target for the facehugger that attacked it.
The Alien on the other hand....
....being a benign species of highly advanced gene farmers,it is summized that the Alien was engineered as a self defence weapon or deterent that,being so perfect in its excecution,so aggressive by design,things went horribly wrong and it decimated its creators and all those trying to flee the homeworld.
Lambert states in the film Alien...'I wonder what happened to the rest of the crew?' Kane soon discovers their fate in the hold of the ship. The crewmembers,are now spore pods/eggs. A self regenerating bio-weapon. Rather ingenious really.