Oh my. This is pretty disturbing. I don’t know terribly much about how DNA works where I’ve never formally studied it, but I’m pretty sure this is a result of a random duplication at conception. What happens when DNA is randomly duplicated? Most of the time, not much, because the DNA in question is in “junk” areas where it doesn’t actually create any proteins because of a previous “stop” codon. Sometimes, however, the DNA that gets duplicated does some very uncanny things. Like give animals two faces.
Hat tip to Jeremy Witteveen via Facebook.