In my previous post, I referenced a couple studies that were done on wild Eevee behavior, and I've gotten a bunch of questions about them (offline, but it's an amusing coincidence to me), so I've decided to expand on it a bit.
The study about evolved Eevees seeking and using evolution stones on their offspring was based on a series of field research projects, documenting the behaviors of wild Eevees and their evolutions in their natural habitats. Before the study was done, the prevailing theory about wild Eevee evolution was that parents would expose their children to evolution stones that were native to their environments - fire stones for Flareons with offspring, for example.
The research was conducted by placing cameras and other passive recording devices in areas where Eevee were known to breed and also live in evolved forms. The research projects were conducted over the course of 5 years, each one of the eight used by the study having a duration of 2 years or more (the longest one was 4 1/2 years).
Thousands of hours of video footage was reviewed, and while it did spark many new research expeditions, it very cleanly concluded that Eevee do not naturally seek out evolution stones and expose their offspring. Not one single instance of an Eevee seeking out an evolution stone was recorded on film. Still images of Eevee nests taken over the course of those years showed not one case of evolution stones being placed in, near, or around the nests. Video of nests recorded the same thing.
The other study that I mentioned, albeit less directly, was about Eevees being semi-migratory and traveling to environments that they felt more comfortable in. This study's field research took much longer, spanning a whole decade. In total, the results of 150 different field research projects were used, many spanning 5 years or more.
Wild Eevees were given tiny tracking devices, usually some kind of ear clip or piercing that would go unnoticed, most commonly during infancy. These trackers were designed to stay with them and fall off naturally after so many years, be it from designed-to-fail piercings, planned fabric decay, whatever the case may be. The biggest risk for the researchers was actually getting the tags on them, which normally involved a team to get or keep the parent evolved Eevee away from the den long enough for another team to tag the infant Eevees and get out.
It's worth noting that these studies actually had human casualties, including death, but not one Eevee or parent was harmed.
The tagged Eevees were monitored over the duration of their studies, and a short time before the trackers were designed to fail and fall off, they were observed from a distance, in whatever habitat they happened to end up in.
Follow-up projects, which numbered about half as many as the tracking projects, involved a team approaching the Eevees that had migrated but had not yet evolved and passively introducing them to an evolution stone that matched closest with the environment they were born in - usually leaving it along a known travel route or near its den but far enough not to prompt it to relocate.
The interactions the unevolved Eevee had with these stones were universally negative. The Eevee, upon noticing them, would either flee outright, or show signs of defensive aggression (bristling fur, growling, occasionally attacking it with a non-contact attack, such as Swift and then immediately fleeing) at the stone while bypassing it, and were wary of the area they discovered the stone for as long as two weeks after it was removed.
Pokéempaths were specifically a part of these teams, and of the 49 field research follow-up projects that introduced evolution stones and recorded reactions, 32 of them included at least one, 19 including three for the purpose of verification. Every single time, the pokéempaths would conclude (unanimously, in the case of multiple-empath teams) that the Eevees were directing their fear or defensive aggression at the stone itself, and that the reactions were not based on a fear of evolving, but on a disdain for that particular evolutionary influence.
Even with all this research done, we still have a lot to learn about the Eevee family, and I'm really excited that I'm going to be adding directly to that pool of knowledge.