In the 1950s, Soviet zoologist Dmitry Belyayev began selectively breeding wild foxes based on how friendly they were. The result is a semi-domesticated red fox, five of which now live in California.
Via Verge Science:
This week, we meet the very cute and very bizarre result of an almost 60-year-long experiment: they’re foxes that have been specially bred for their dog-like friendliness toward people. We do a little behavior research of our own, and discover what scientists continue to learn from the world’s most famous experiment in domestication. The fox experiment continues under the supervision of Lyudmila Trut at the Institute of Cytology and Genetics. Her book “How to Tame a Fox (and Build a Dog)”, co-authored by Lee Alan Dugatkin, details the history and science behind the experiment.
There's a distinction between domesticated animals like these and socialized wild animals. You can raise a chimp from infancy to be socialized around humans, but it still might rip your face off one day because it is not domesticated.
Belyayev simultaneously bred the most aggressive foxes with each other, and generations later will lunge at anyone who approaches their cages. Meanwhile The nice foxes even started to look different: "They even started sporting some of the signature biological features of domesticated dogs, like curly tails and floppy ears."