The gene passed down from one person to another, resulting in a future engineer. Tell-tale signs in such a person include an inexplicable love for creating problems to solve (technical or mechanical) when there's absolutely no need to, the constant need to find solutions for everyday issues that no one else gives a crap about, know-it-all syndrome, and the inability to admit they're wrong. Are usually social inept to some degree.
On a side note, this is also why engineering jobs have hierarchies (like worker, head engineer of division 2, chief engineer of all divisions, etc.) If they didn't have an orderly and number-oriented way to say "the bill stops here" they'ed never get anything done.
Normal person: I'm bored, I'd go on the computer but the internet's so fricking slow today...
Person with engineering gene: I'm bored. I think I'll take apart the computer. Oh, look, the internet's not working. I think I'll spend the whole afternoon solving that problem