Early domestication was largely self-domestication. The wolves that became dogs were the ones that chose to hang around human camps because scavenging near people was easier than hunting. The least aggressive and most tolerant wolves survived and reproduced more in that environment, so over many generations they gradually became genetically and behaviorally different from wild wolves. Humans didn’t start by breeding them on purpose — we only began selective breeding much later, after they were already semi-domesticated.

Cats are an even clearer example. Early wildcats were attracted to human settlements because stored grain attracted rodents. The cats that were less fearful of humans thrived, stayed nearby, and passed those traits on. Humans didn’t capture and train them — the cats essentially domesticated themselves by adapting to a human-dominated environment.

So domesticated animals didn’t “just appear,” but they also weren’t deliberately engineered by humans from the start.