there are many theories in this regard, some say space jockies or some alien race created them, or it could be natural evoltuion. but lets look at the facts that we do know for sure, then lets dive into theories.
1. yes there were xenomorph eggs on the derelict station
2. yes there was a chest-bursted "space-jockey" on the derelict also
3. xenomorph have the extreme ability to evolve to said situation (i mean look at alien by the end of one day it had aposible thumbs!)
4. according to alien books there was a supposed homeworld (ended up being blown up in ALIENS: EARTH HIVE)
5. said homeworld was completly contradicted when in ALIENS: FEMALE WAR the "mother" queen was somewhere completly different on a more xenomorphiszed world
6: supposedly the "space-jockies" and yautja were at war.
7: according to ALIENS: EARTH HIVE at least one "space jockey" has an extreme hate to xenomorphs and maybe all life
8: xenomorphs seem bio-engineered but it has never been proven.
9: there has been more than one "space jocky" ship containing xenomorph eggs.
10. the "space jockey" was emiting a warning from the derelict ship
now maybe we should get on to the theories
1. it is beilved that the space jockies did create xenomorphs as a bio-weapon, which makes sense since humans are always trying to find use do the exact same thing. but the question was who was the bio weapon to be used on. many beilve it was the to be used against the yautja, since the yautja and the space jockies were supposedly at war.
argument against:the whole war scerio has never been proven, or the bio enginering,
2. basically the same as above except for the use. another likly possibilty is that the xenomorphs were created to end all life, to cleanse the galaxy if you will. i mean look at what ever planet the xenomorphs have tainted, all life there ceases to exsist. but it ended up back firing on many ships as containment wasbroken and the "space jocky" piolet became infected. while this may not be all space jockies it could just be a extremest faction much like terrorists
argument against: as said beforre the bio engineering has never been proven. also why would the "extremist space jocky or any space jockey" trying to kill all life emit a warning? also accourding to said books aliens have not completly taken over all planets. look at ALIENS: EARTH HIVE there was a complete ecosystem where the xenomorphs did not dominate on said "home planet"
3. either of the above except that the "space jockies" found and captured the aliens to use as their weapon
argument against: while the only planet seemingly vialble to be the aliens homeworld (in ALIENS: EARTH HIVE it was missing the "queen of queens" while said other planet that had this mighty queen seemed to have been more infected for what seemed to be a much longer time"
4. EVOlUTION. this theory has valid points, mainly that these creators do evolve extremly fast especially since they are parsites taking what they need from said host to live, which one most remember is very base the alien form generally stays the same just slightly altered to fit their situation. also one should also reilize it has been proven by our earth scientists today if we are ever to find alien life it will be some form of insect. i mean look at our planet and see how many different types of insects there are. so guess what xenomorphs are parsitic insects. also as for the concern of the acid blood. there is biology to it. one must know that the blood is not "pure acid" it is just a extremly high acidic content to it, which works as a defense mechanism, we are selves could have highly concentraited acidic blood but our bodyies cant support it we dont have enough of a alcali substance in us to counteract it, while xenomorphs do. (thats why they look wet)
argument against: evolution takes millions of years to adavance while to the xenomorph it takes a matter of hours, there go they have the touch of creation
5: the last theory i can think of at the moment is that the "space jockies" were merely a form of transport for the xenomorph eggs. that they would plant xenomorph eggs on said plaent for the yautja to hunt.
argument against: if indeed the yautja and the "space jockies" were at war why would they help each other unless the came to a truce, the space jockies lost in which they were forced into a treaty of versailles situation
take you pick invent your own, just please dont just say bring information to back it up
"He who fights monsters should see to it that in the process, he does not become a monster." ~Nietzche