Haven't chickens for example been genetically altered through breeding to grow bigger and faster so they are ready for slaughter at 8 weeks? Maybe a question of semantics but I would class that as an artificial enhancement.
That'd be down to selective breeding for birds that pack on the weight more quickly. That, and raising the birds in sheds. Your average supermarket chicken or duck is typically somewhere around 8 weeks old (I know that as there's a duck farm nearby, and it's easy enough to keep track of when they clear the sheds). Likewise a cheap turkey is about 3 months old.
This is exactly why I prefer to buy free range poultry if I can. The birds are more expensive because they are slower growing and at least twice the age of the above (ergo longer time on the farm), have room to roam (much smaller density) and therefore are less stressed. But you really do notice the difference in flavour and texture.
That said, farmers have always looked to maximise the size and productivity of their livestock by breeding for specific traits. You only need to look at the agricultural / livestock paintings of the 18th and 19th century to see that this is nothing new. But this has vastly accelerated since the second world war - where intensive farming methods were employed to help ramp up food production for a very hungry nation. The UK was broke post-war, and the country was committed to helping to feed a devastated Europe as well as themselves.
