Cheese is a pretty weird thing when you think about it.  Someone had to come up with the idea of taking a bunch of milk, adding bacteria, letting it basically go bad, and waiting to eat it until mold had grown on it. 

And, if that grosses you out, just wait.  It turns out that the fungi in cheeses like blue cheese aren’t just sitting there, waiting for you to eat them.  They’re getting it on.  Here’s Nitty Gritty Science on what’s going on:

Until pretty recently, a big chunk of fungal species were thought to reproduce without sex–until people really started to look.  It turns out, there’s a lot more sex going on in the fungal world (on the down-low) than people thought.  And that includes fungi that are used to make delicious blue cheese.  Jeanne Ropars and colleagues in France, the home of Roquefort cheese, looked at the genomes of the mold species used in this particular cheese to see what kind of funny business was going on in their snack of choice.  They found much more diversity than could be explained by asexual reproduction.  And even more telling, the genes used by fungi to find mating partners have been kept intact and functional by evolution, meaning there’s probably some sex going on. 

It turns out that this is actually a good thing for cheese makers, since producing new forms of cheese really means producing new forms of mold.  When the mold is reproducing asexually, new forms come from random mutations within one strain that’s simply duplicating itself.  But when different mold strains are getting it on, they create way more new strains and way more new cheeses. 

The paper behind all this (titled “Sex in Cheese: Evidense for Sexuality in the Fungus Penicillium requeforti”) says:

In this species of high industrial importance, the induction of a sexual cycle would open the possibility of generating new genotypes that would be extremely useful to diversify cheese products. 

Essentially, the researchers discovered that a fungus has all the genes and mechanical bits that it would need for sex.  And not only is it capable of sex, there is evidence that it’s actually doing the deed.  Here’s Nitty Gritty Science again:

Next, there were plenty of clues left by evolution that sex is either happening right now in your cheese, or that it had been happening until fairly recently.  The aforementioned sexy-time genes were evolving by purifying selection.  This is a kind of evolution that keeps things from changing (I know, sounds like the opposite of evolution).  Genes that are really important for life (or sex, and really is there a difference?)  shouldn’t change.  But mutations will happen, so evolution has to get in there and remove anyone carrying those mutations from the population.  Basically, get mutations in really important genes, those genes no longer work, and you die.  If there was no need for sexy-time genes anymore, then there would be no problem with mutations building up.  There were also footprints of sex in the genome.  When sex occurs, DNA gets reshuffled.  The researchers found evidence of this kind of reshuffling in some of the chunks of DNA they looked at, meaning that sex had to occur at some point in the recent past. 

Of course, no one has actually seen cheese mold having sex.  But genetics doesn’t tend to lie.  Perhaps this is a paternity case for the Maury Show. 

More from Smithsonian.com:

Marvelous Macaroni and Cheese

Making Homemade Yogurt and Cheese