THE ORKS, page 50-51, paragraph 9
Although it may seem very strange to humans, these Oddboyz all possess an intuitive understanding of complex technical matters. For example, a Mekboy knows how to create engines and generators even though he has never been taught to do so. If asked where his knowledge comes from he might say that engineering and mechanics were in his blood. If the Imperium's scientists are correct then this would almost literally be true! If appears that bound up within an Ork's genetic structure are artificial DNA strands which carry knowledge. Possibly these DNA strands were implanted into the Ork metabolism by the Brain Boys to enable the Orks to survive without their masters. As an Ork matures any latent knowledge inherent in his genetic structure starts to make itself felt, and he assumes a role in society to which he is best suited.