Exercise shrinks your penis and coffee rouses your bowels. It’s not your imagination. It’s science.

The depths of the female brain may be unfathomable, but the superficiality of the male mind is no easier to decipher. Why do we struggle to remember our loved ones’ birthdays yet retain an encyclopaedic knowledge of craft beer and sports stats? Why, after all these years of living in our skin, are we more fascinated with our own bodily functions than preserving the world for future generations? Frankly, we don’t know, but we can certainly explain why you feel like puking when someone else hurls.

1. Why Do I Like My Own Body Odours Better Than Everyone Else’s?
Survival of the fittest entails avoiding other people’s nastiness. Infection-causing bacteria on their bodies can be a source of disease. If you were drawn to instead of being repulsed by the unpleasant odours these bacteria sometimes emit, you’d be more susceptible to illness and death. It’s that simple, says Nina Strohminger, author of The Hedonics of Disgust. (What? That’s not in your bathroom library?) Here’s another way to look at it: if you vomited every time you took a dump, you’d be highly irregular. You’re just not genetically designed to feel revolted when you catch a whiff of yourself. And, per an Evolution and Human Behaviour study, you don’t find your loved ones’ disgusting acts as gross as a stranger’s. That’s because you share the same parents or living space, and they pose less of a disease risk.

2. Why Does Coffee Loosen My Bowels?
Research has shown that a good grind gives about a third of people the urge to go. Within approximately four minutes of ingestion, both regular and decaf coffee stimulate the end of the colon. The timing can vary, but the urge can last 30 minutes or longer. While the exact compounds behind the effect are unknown, coffee consumption increases your body’s levels of two hormones, gastrin and cholecystokinin, that speed up gut motility and stimulate the liver to secrete digestion-revving bile, explains gas troenterologist Kathlynn Caguiat. Plus, drinking your coffee first thing in the morning can trigger what’s called a “gastrocolic reflex.” That’s your body’s tendency to make room when something new comes into the stomach.

3. Why Is Popping a Pimple So Satisfying?
Even though dermatologists warn about the risk of infection and scarring, pimples beg to be popped just like Everest beckons to be climbed. Popping rids the skin of acidic pus and eases pressure, says plastic surgeon Julius Few. And as the pain eases, you get a shot of dopamine, the feelgood brain chemical.

4. Why Do I Get the Urge to Vomit After Seeing Someone Else Doing It?

Call it an evolutionary gag reflex. If thousands of years ago someone in your tribe was vomiting, the reason was probably something besides drinking too much hooch. “They were either sick or had ingested something poisonous,” says Strohminger, “and chances were good you’d eaten some too. So throwing up helped prevent you from getting sick.”

5. Why Am I Obsessed with Younger Women?
Because you’re a male Homo sapiens. Duh. “In terms of evolution, men needed to spread their seed for their genes to survive. And until the past 100 years or so, fathering a slew of kids meant having more helping hands on the farm,” explains Helen Fisher, a biological anthropologist and the author of Anatomy of Love. This is why men of all ages are attracted to women in their physical prime. It may even explain why, according to a 2014 Pew Research Center survey, 20% of us choose a woman at least 10 years younger when we marry a second time.

6. Why Does My Penis Shrink When I Exercise?
When you hit it hard in the gym, all of those muscles swell with 15 to 20 times more blood than they have when they’re at rest, says exercise physiologist Mike Nelson. The blood has to come from somewhere, so parts of the body not directly involved with the effort give up some of their share – including luxury tissue like your penis. The resulting dip in bloodflow in the area is so dramatic that it can make grown men look prepubescent, says urologist Brian Steixner. That won’t change much even if a spandex-clad beauty starts doing squats nearby. Adrenaline, which is released during exercise to increase work capacity, blocks dopamine’s efforts to pump blood back into your penis.

7. Why Must I Turn My Head and Cough When the Doc Grabs My Testicles?
When you cough (turning your head is just being polite), you increase pressure in your abdomen. If you have an inguinal hernia, which affects 27% of men, the pressure forces fat tissue and parts of the intestine to poke though abdominal wall muscles and possibly down into your scrotum, says surgeon Steven Beanes. With a hand firmly on your groin, the doctor can feel anything amiss. Detecting groin hernias early lowers the risk of intestinal tissue death, which could lead to bowel-removal surgeries and even threaten your life.

8. Why Do Old People Smell So Darn Funky?

Certain conditions that tend to be more common among older people, such as kidney and liver disease, can cause toxins to build up in the body or acidity to increase, which can lead to a distinctive, unpleasant smell, according to William Dale, who teaches geriatrics at the University of Chicago. Also, with diabetes, excess sugar in the blood can cause a sweet smell and result in bad-smelling fungal infections of the skin. Your grandpa may not notice these odours because people’s sense of smell tends to dull with age. So if you suddenly detect something funky (and it’s not Wild Cherry on the oldies station), you may want to diplomatically suggest that he schedule a checkup. Incidentally, humans may be able to determine age ranges based on body odour, a 2012 PLOS One study suggests.

9. How Many Kilojoules Do I Lose When I Take a Dump?

Ideally, zero, although you do burn a few through muscle effort. Your small intestine is nicely designed to absorb all the kilojoules from the food you consume, after which every calorie is either burned for energy or stored as fat. It’s a very efficient system in which nothing is wasted, says Dr Caguiat. However, there is a condition called steatorrhea, in which the body struggles to absorb dietary fat, causing greasy, foul-smelling stool. As a result, hundreds of kilojoules (35 kJ per fat gram, to be exact) go down the toilet. Generally, steatorrhea results from pancreatic conditions, a low level of bile salts, or such weight-loss drugs as Alli. Fat malabsorption can lead to diarrhea and, in some cases (yikes!) anal leakage.

10. If Cleaning My Ears with a Cotton Swab Is So Bad, Why Does It Feel So Wonderful?
The skin covering your ears has lots of extremely sensitive nerve endings, and many of them ultimately connect with internal organs. So getting your Q-tip on sends a cascade of pleasure signals through out your body’s various sensory tissues and organ systems, says Amber Luong, an associate professor of otorhinolaryngology (which sounds much better than it looks) at the University of Texas McGovern Medical School. Those ultra sensitive nerve endings are one reason why ear kisses (and having sweet nothings whispered into those ears) is such a big turn-on for men as well as women, adds sex therapist Tammy Nelson.

11. Why Would Anyone Choose To Become a Proctologist?
They come for the massive salary and stay for the huge impact they can have on people’s lives. (Colorectal cancer has up to a 90% survival rate if it’s caught early.) And just so you know: they’re no longer called proctologists; they’re colorectal surgeons now.