Reminder,
Gardevoir and its evolutionary line are "Urban" Pokemon, implying that their natural habitat is among people.
All other Urban pokemon are Pokemon would expect to see in towns (this is a Fire Red/Leaf Green only feature so any new Pokemon aren't on it, but using the current pokemon in the list we can assume similar mons are also part of it);
Pet-like: Meowth line, Snubble line, Eevee line, Smeargle
People Helper: Chansey Line
People Made: Grimer line, Shuppet line, Voltorb line, Porygon line.
People-Like: Abra line, Ralts line, Smoochum line, Tyrogue line
We can assume the People-Like Urban Pokemon are kept as close companions and are the most likely candidates for pokemon people used to marry. Why else would usually wild animals come to find urban areas to be their natural habitat? People must have brought them in.
I made a theory a while back, when XY first revealed M-Gardevoir and the Pokemon Origins anime.
According to Pokemon Origins (and backed up by XY and ORAS), a Pokemon can only achieve Mega Evolution if it and its master share a close bond. Gardevoir's mega takes looks like it's wearing a bridal gown.
Surely you see where I'm going with this.
Gardevoir achieves mega evolution when it shares a close bond with its master. Gardevoir is one of the commonly married Pokemon. It's mega form could be reference to this, a subtle hint to expand upon Gen 4's folklore.
Made you think.
