Okay, So in say 1800ishAD Humanity achieves Biodome(no not the Pauley Shore one) status, Then doesn't show any real advancement in Evolution in 200 Years, and Decides to wipe the planet,
but not enough to cause permanent harm, so future generations of lavoid could have a grounds to Harvest different DNA strands, which makes sense if assuming only earth like planets could support life(anyone know how many known ones of those there are?) and if a Lavoids Lifespan is 65Mil + Travel Time There might be a Lavoid on every Planet.
I think that Lavos just generally reviewed the evolution of mankind through the ages and found out that there were undesirable genes popping up.
A lot would have happened between 1000AD( plus all those other years in CC) and 1999AD.... not only tecnologically, but also, say, in the creation of nuclear arms or power plants.... what if a nuke went off, or a power plant like chernobyl blew up?
IRL children who live around Chernobyl are born with twice as many genetic defects as children elsewere... so my bid is an undesirable mutation caused by a nuclear force, or general genetic breakdown as can be seen in our modern society today (some allergies, the lack of being able to properly survive without aquedate hygiene etc.)
Keep in mind that the 1999AD in CT is at leat 50-100 years more advanced than IRL today, so it could be PARTIALLY because of the lifestyle in the domes
That combined with tech and stuff like that could have triggered the 1999AD catastrophe where Lavos pops out and says hi...