When it comes to deciding what tastes good, all human beings and most animals have four things in common: They like sweets, crave salt, go for the fat, and avoid the bitter (at least at first). These choices are rooted deep in biology and evolution.

In fact, you can say that whenever you reach for something that you consider good to eat, the entire human race — especially your own individual ancestors — reaches with you. Here’s something to chew on: The foods that taste good — sweet foods, salty foods, fatty foods — are essential for a healthy body.

• Sweet foods are a source of quick energy because their sugars can be converted quickly to glucose, the molecule that your body burns for energy. Better yet, sweet foods make you feel good. Eating them tells your brain to release natural painkillers called endorphins.

Sweet foods may also stimulate an increase in blood levels of adrenaline, a hormone secreted by the adrenal glands. Adrenaline sometimes is labeled the fight-or-flight hormone because it’s secreted more heavily when you feel threatened and must decide whether to stand your ground — fight — or hurry away — flight.

• Salt is vital to life. Salt enables your body to maintain its fluid balance and to regulate chemicals called electrolytes that give your nerve cells the power needed to fire electrical charges that energize your muscles, power up your organs, and transmit messages from your brain.

• Fatty foods are even richer in calories (energy) than sugars. So the fact that you want them most when you’re very hungry comes as no surprise.

• Which fatty food you want may depend on your sex. Several studies suggest that women like their fats with sugar — Hey, where’s the chocolate? Men, on the other hand, seem to prefer their fat with salt — Bring on the fries!

Marvin Harris was an anthropologist with a special interest in the history of food. In a perfectly delightful book called Good to Eat: Riddles of Food and Culture (Simon & Schuster, 1986), Harris posed this interesting situation:

Suppose you live in a forest where someone has pinned $20 and $1 bills to the upper branches of the trees. Which will you reach for? The $20 bills, of course. But wait. Suppose that only a couple of $20 bills are pinned to branches among millions and millions of $1 bills.

Does that change the picture? You betcha. Searching for food is hard work. You don’t want to spend so much time and energy searching for food that you end up using more calories than the food that you find can provide.

Substitute “chickens” for $20 bills and “large insects” for $1 bills, and you can see why people who live in places where insects far outnumber the chickens spend their time and energy on picking off the plentiful high-protein bugs rather than chasing after the occasional chicken — although they wouldn’t turn it down if it fell into the pot.

So, you may say that Harris’s first rule of food choice is that people tend to eat and enjoy what is easily available, which explains the differences in cuisines in different parts of the world. Here’s a second rule: For a food to be appealing (good to eat), it must be both nutritious and relatively easy or economical to produce.

A food that meets one test but not the other is likely to be off the list. For example:

• The human stomach cannot extract nutrients from grass. So even though grass grows here, there, and everywhere, under ordinary circumstances, grass never ends up in your salad.

• Cows are harder to raise than plants, especially under the hot South Asian sun; pigs eat what people do, so they compete for your food supply. In other words, although they’re highly nutritious, sometimes neither the cow nor the pig is economical to produce.

This anthropological explanation is a reasonable argument for why some cultures have prohibited the use of pigs and cows as food.

Virtually everyone instinctively dislikes bitter foods, at least at first tasting. This dislike is a protective mechanism. Bitter foods are often poisonous, so disliking stuff that tastes bitter is a primitive but effective way to eliminate potentially toxic food.

According to Linda Bartoshuk, Ph.D., professor of surgery (otolaryngology) at the Yale University School of Medicine, about two-thirds of all human eings carry a gene that makes them especially sensitive to bitter flavors. This gene may have given their ancestors a leg up in surviving their evolutionary food trials.

People with this gene can taste very small concentrations of a chemical called phenylthiocarbamide (PTC). Because PTC is potentially toxic, Dr. Bartoshuk tests for the trait by having people taste a piece of paper impregnated with 6-n-propylthiouracil, a thyroid medication whose flavor and chemical structure are similar to PTC.

People who say the paper tastes bitter are called PTC tasters. People who taste only paper are called PTC nontasters. If you’re a PTC taster, you’re likely to find the taste of saccharin, caffeine, the salt substitute potassium chloride, and the food preservatives sodium benzoate and potassium benzoate really nasty.

The same is true for the flavor chemicals common to cruciferous vegetables — members of the mustard family, including broccoli, Brussels sprouts, cabbage, cauliflower, and radishes. No such ambivalence exists among people who’ve gotten truly sick — I’m talking nausea and vomiting here — after eating a specific food.

When that happens, you’ll probably come to like its flavor less. Sometimes, says psychologist Alexandra W. Logue, author of The Psychology of Eating and Drinking, your revulsion may be so strong that you’ll never try the food again — even when you know that what actually made you sick was something else entirely, like riding a roller coaster just before eating, or having the flu, or taking a drug whose side effects upset your stomach.

If you’re allergic to a food or have a metabolic problem that makes digesting it hard for you, you may eat the food less frequently, but you’ll enjoy it as much as everyone else does. For example, people who cannot digest lactose, the sugar in milk, may end up gassy every time they eat ice cream, but they still like the way the ice cream tastes.

Does it matter whether you like your food? Yes, of course, it does. The simple act of putting food into your mouth needs to stimulate the flow of saliva and the secretion of enzymes that you need to digest the food. Some studies suggest that if you really like your food, your pancreas may release as much as 30 times its normal amount of digestive enzymes.

However, if you truly loathe what you’re eating, your body may refuse to take it in. No saliva flows; your mouth becomes so dry that you may not even be able to swallow the food. If you do manage to choke it down, your stomach muscles and your digestive tract may convulse in an effort to be rid of the awful stuff.