Some fighters just seem born with it. That so called "killer instinct" that appears to us as the ghost in the machine. A supernatural sense that allows a fighter to make every strike count, each punch a five knuckle magnet to their opponent's skull. Anderson Silva has it. Chris Weidman seemed to have it against Mark Munoz. Like the great white before them, do fighters quite literally ‘smell blood in the water'?

Even within the world of science, there is no less understood sense than the sense of smell. Part of that is by design. Much of who we are comes from the viruses we inherited, creating the so called "junk DNA" that rules our genetic makeup. The eight hundred olfactory genes that give way to our sense of smell make up about 3% of our genome. That's a large percentage for something we don't know much about.

So what purpose does the sense of smell serve?

Historically, it was quite vital. In evolutionary terms, a sense of smell was important for locating food, settling on a mate, and identifying predators. But as we evolved to stand upright, more genes became dedicated to processing vision, and smell took a ‘backseat'. But that's not to say it was any less important.

In some ways, this is already obvious. Bad breath is more than an indication of eating one too many Taco Locos, for example. The link to bad health can get a lot weirder, however. An impaired sense of smell has long been associated with Alzheimer's, and Parkinson's, but in fact, even more specific illnesses can be connected with corresponding odors; like the nail polish remover of ketoacidosis, the smell of lighter fluid that accompanies preeclampsia, the ether that indicates schizophrenia, or the smell of cheese that points in the direction of a urinary tract infection.

Perhaps even stranger are the experiments that suggest smell can influence mate selection. This was the thesis Swiss scientist Claus Wedekind tried to validate with the famous "sweaty t-shirt" test where women would identify which shirt (shirts worn by men for two nights without deodorant, or cologne) they found to be pleasant or sexy based on scent. The groups were chosen according to their MHC genes, and women in this experiment unconsciously preferred men with more distinct MHC genes.

To clarify, MCH genes control how our immune system defends itself against disease. As Sheril Kirschenbaum notes in the Science of Kissing, "MHC diversity is also very important for producing offspring with flexible and versatile immune systems. Children benefit most when they have distinct MCH genetic material from their parents. This makes detecting MCH variation in a partner very important for the health and survival of the net generation."

Not oddly enough, when a study in 2006 at the University of Mexico was done to look at couples who had similar MHC genes...well...let's just say that the men were more likely to find a boiling pet rabbit in their stew.

This isn't the most bizarre experiment to elucidate the subconscious value of smell. For fighters, perhaps they'll find it interesting to note that there is evidence to suggest we can detect fear from another's sweat.

Rather than describe the experiment, you need to read it for yourself.

Our sense of smell may even help us to pick up on the emotional state of those around us. This idea has been highly controversial, but work by Mujica-Parodi suggests we can sense another's fear from their sweat. At the time, she was working on a way to assess a person's vulnerability to stress, and needed a reliable way to scare her subjects, without socially loaded words or pictures that might mean different things to different people. That's hard to do, says Mujica-Parodi: "You can't mug somebody in a scanner." The answer came from nature. Rats are known to be able to smell each other's fear, leading them to "freak out" if placed in an empty cage in which another rat has just seen a predator. Mujica-Parodi figured humans might do the same thing. To test the idea, her team took sweat samples from people doing a skydive for the first time. When they presented the samples to unrelated subjects in an fMRI scanner, they saw activation of the amygdala - the brain area that normally lights up in studies of emotion. This did not happen when sweat samples came from the same skydivers pounding a treadmill. Mujica-Parodi's team next tested whether the smell of fear sweat affected people's responses to various facial expressions - angry, ambiguous or neutral. Normally, we would pay more attention to angry faces, because they pose a threat, but after smelling the fear sweat, the participants gave all three types the same attention (Social Cognitive and Affective Neuroscience, in press, DOI: 10.1093/scan/nsq097). "It forced the brain to pay attention to things that otherwise it wouldn't consider worth its time," Mujica-Parodi says.

Many movie villains have often made this their mantra: "I can smell your fear". Perhaps Dr. Lecter was being more literal than we assumed.

Just as interestingly, Catherine de Lange's article goes on to document how some scientists suggest our sense of smell can be honed, molded, and somehow improved.

I can't imagine what value a fighter might get out of training this supersense. But who knows...maybe there's value in sniffing an air polluted by an opponent's emotional state, and being able to react accordingly.

Maybe Tyron Woodley would have been more aggressive. Well, in a parallel universe where Nate Marquardt simply isn't the better fighter, maybe. But I suppose any little bit helps when you're fighting to prevent your limbs from being broken.