For most of history, the majority of people were so busy trying to survive, they didn't worry all that much about how happy they were. That's probably still true for most of the 2.8 billion people who live on less than $2 a day.

Being concerned with levels of happiness or working to improve happiness for yourself, for family members or for others in your community is a mostly modern phenomenon of the well-off. Many people will use that logic to argue that it's a silly, superficial concern.

But it's not. After all, what's the point of working to ensure that everyone around you is healthy, cared for and able to work toward their dreams if not to pursue happiness once those basics are taken care of? It's natural to think about emotional or psychological states once your main needs are met, and human beings in the past also examined happiness — once they got to a point where they weren't scraping by. In fact, they helped define what we mean by "happy" today.

What is happiness?

Greek philosophers (and religious thinkers of various stripes) usually define happiness as a holistic idea — living a good life that gives satisfaction beyond just a fleeting feeling of temporary pleasure. The Greek word eudaimonia translates to happiness, but it's understood in its historical context as "human flourishing," and it's a central concept in Aristotelian ethics. Thomas Jefferson certainly had something greater than the pleasantness of the day-to-day when he wrote of Americans' right to the "pursuit of happiness" in the Declaration of Independence.

Today, there's still disagreement on what, precisely happiness is. Some qualify it as joyfulness, while others suggest it's contentment. Still others define it as acceptance by a group or when we are praised by those we respect. Achievement of goals, giving of oneself and unexpected delights are other ways of finding happiness, depending on who you talk to.

The definition of happiness seems cloudy, but that being said, most people know it when they feel it — like love, sadness and jealousy, all of which are emotional states that can give rise to a number of seemingly shifting definitions.

So who is really happy?

In recent years, psychologists and social science researchers have asked people about how happy they are via large-group surveys to figure out where the secret to happiness lies. Lists of the happiest cities and countries abound. Down on the more granular level, it's generally found that older people are happier than younger. A 32-year study with more than 28,000 participants by the University of Chicago found that more than one-third of people at age 88 considered themselves "very happy" whereas less than 25 percent of 18- to 20-year-olds felt the same way.

Ilse Siegler, an 84-year-old retired nurse manager in Chicago told ABC News: "Contentment as far as I'm concerned comes with old age ... because you accept things the way they are," she said. "You know that nothing is perfect." Studies generally agree that happiness reaches a nadir at age 50 and then increases from there pretty much until you die.

Yes, people with more money are happier, but only to a certain point. (After your income reaches $65,000 to $120,000, depending on where you live, your happiness levels won't improve much with more cash.) Young women are happier than young men, but by middle age, men are happier than women, overall. Religious people are happier than atheists, but as Sandra Upson writes in a Scientific American column, that depends on the culture: “Religious people may be happier than their godless counterparts, but only if the society they belong to values religion highly, which not all societies do.”

Research has found that at least some of how happy we are is out of our control. In her book "The How of Happiness," researcher and UCLA psychology professor Sonja Lvubomirsky reports that research has found 50 percent of your happiness level is genetic (based on twin studies): 40 percent is determined by yourself and about 10 percent is the result of your surroundings. So a chunk of your happiness is controllable by you, but not all of it, which squares with what research has found: You can't control age or sex, but income levels and some health specifics can be controlled.

To be happy, stop focusing on happiness

But all this attention to happiness has plenty of skeptics and critiques. How to achieve happiness and who has more of it is the wrong question to ask and the wrong feeling to focus on, says Mark Manson, author of the book, "The Subtle Art of Not Giving a Fu**." He told Mother Jones magazine, "In general, people have spent way too much time trying to feel good all the time. Instead they should focus on deciphering what's important and what's not. Because problems are inevitable, pain is inevitable, and the only really reliable way to persevere or deal with those problems and pain is to find a worthy cause or a worthy reason for dealing with it."

Succeeding through difficulty is one way to find happiness over the long-term, even if in the moment you don't feel happy doing the work to get there. For example, writing a book, completing college or graduate school, or building a house are all things that require a lot of frustration, work and effort to achieve, but most people feel are "worth it" and eventually contribute to overall happiness.

Manson goes on to explain: "The quality of your life is determined by how good your problems are, not how awesome you feel all the time. The whole point of [my] book is that self improvement isn't about getting rid of pain. It's about not giving a fu** about pain. That's what growth is. It's getting to the point where the pain you're sustaining is a worthwhile thing to endure."

But maybe even Manson is overthinking things. In Gretchen Rubin's book, "The Happiness Project," she spent a year pursuing happiness in her own life; her memoir about what she figured out spent years on the New York Times bestseller list. She advises to start with the basics, something many people forget: She writes: "When I began my Happiness Project, I realized pretty quickly that, rather than jumping in with lengthy daily meditation or answering deep questions of self-identity, I should start with the basics, like going to sleep at a decent hour and not letting myself get too hungry. Science backs this up; these two factors have a big impact on happiness."

Sometimes simple pleasures — and solutions — can be the key to happiness.

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.