It's not that simple, of course. Human nature cannot be neatly parsed and paired like Noah's ark-bound animals: "seven deadly sins" matched against "seven holy virtues."
Indeed, nothing could be more confounding than the nature of human nature. Why do people behave as they do? Is it genes? Is it the environment? Can we ever know?
Well, yes and no. Any answer seems invariably to start with the old nature-versus-nurture dispute. No one seriously believes any more that human behavior is the sole product of either.
Maybe it's not even meaningful to discuss nature and nurture as separate forces, said Richard Robins, a professor of psychology at the University of California Davis.
"We now know that an individual's genetic makeup has a profound effect on the environment, and that conversely, the environment has a profound effect on the way genes are expressed," Roberts said.
"The way a child is parented - the parenting environment - is influenced by the child's temperament, which is strongly influenced by genetic factors. Children who are difficult by nature receive poorer parenting than those who are easy by nature. Conversely, the type of parenting a child receives influences the way genes related to temperament and other aspects of behavior are expressed and regulated."
Almost routinely these days, there are reports citing new evidence linking biology to distinct behaviors.
Take gluttony, one of Prudentius' seven deadly sins. Researchers now estimate obesity may be 50 percent to 70 percent heritable. Variations in genes and their functionality appear to predispose some people to becoming overweight more easily. Genes can directly cause obesity in certain disorders like Bardet-Biedl syndrome and Prader-Willi syndrome.
Or wrath, another of the deadly sins. Earlier this year, University of Pittsburgh researchers reported that behaviors like anger, hostility and aggression appear rooted in variations in a serotonin receptor gene. Serotonin is a brain chemical that regulates mood, appetite and sensory perception.
Or sloth. Scientists at the National Institute of Mental Health have found that when they suppress a gene involved in reward-learning, test monkeys become workaholics, laboring tirelessly without payoff.
"This was conspicuously out of character for these animals," said Dr. Barry Richmond, a researcher in the NIMH Laboratory of Neuropsychology. "Like people, they tend to procrastinate when they know they will have to do more work before getting a reward."
Still, no one has yet found a singular gene for obesity, anger or sloth; and no one expects to. The human genome consists of just 30,000 genes, not the 100,000 or more of early estimates. That's far too few to account for every form of human behavior, say scientists like Stanford University biologist Paul Ehrlich. Heck, it's just twice the number of genes in a fruit fly.
So obviously genes work in tandem, scientists say. They provide not the final blueprint of life, but a really good outline that is subject to constant revision. Throughout life, genes switch on and off, frequently in response to their environment.
For example, researchers have watched genes in nematodes literally light up when the worm experiences something new. In humans, fear, worry and anger spur the production of stress hormones that affect the way genes code for proteins: a biological process altered by behavior.
Ehrlich has asserted that there's no such thing as "human nature" per se. The interplay between a person's genes and the environment is simply too complicated and variable. Every individual is unique.
Nonetheless, some human behaviors are universal. A smile means the same thing in all cultures. If science can somehow dissect these basic behaviors, sorting out what's genetic from what's environmental, then perhaps we will better understand ourselves and our natures.
ALTRUISTIC IMPULSES
Altruism, one of the seven holy virtues, has long been a subject of study. In the early 20th century, philosophers and scientists offered up a handful of theories to explain why people make sacrifices - sometimes of their lives - for strangers or abstract ideals.
The dominant theory explained that newborns were basically "blank slates" upon which parents and peers, culture and the environment wrote the rules of living. We were moral animals because that's how we were taught.
Or maybe it was innate, said another theory. Humans were "noble savages" who lacked evil intent. In this case, it was society that corrupted.
A third theory suggested people possessed "a ghost in the machine," an entity separate and different from the body. This invisible, non-biological something - the mind or soul, perhaps - guided our conduct.
By and large, these ideas have been undermined by hard science. We are not noble savages. Our history is too fraught with conflict and violence. If there is a "ghost in the machine," it is unprovable. When brain function ceases, so does the person.
In his 2002 book "The Blank Slate: The Modern Denial of Human Nature" (Penguin, $16), Harvard University cognitive scientist Steven Pinker says it's clear humans arrive in the world with at least some innate abilities and social behaviors.
Newborns, for example, possess intuitive understandings of how the world works and are primed to learn language. We all put family first, but display a distinct propensity to share.
In a clever experiment investigating the connection between genes and altruism, researchers at Hebrew University offered online participants the sum of $12, giving them the option of keeping all of the money or sharing it with a stranger. Then the scientists looked at the participants' genomes.
They found that a gene called AVPR1, which codes for a hormone linked to social bonding, varied between those who gave away some of their money and those who did not. In participants who displayed greater generosity, a section of AVPR1 called the promoter was longer. The promoter is the part of the gene that allows cellular machinery to read the gene and carry out its instructions. A longer promoter can result in greater gene activity.
Altruism may be deeply rooted in very ancient genes. A version of the AVPR1 gene is also found in voles, mouselike rodents known for their social bonds. Even more fundamentally, evolutionary biologists David Queller and Joan Strassmann at Rice University have found that the presence or absence of a single gene influences whether individual slime mold amoebae sacrifice their lives to promote survival of others.
"Our work indicates that slime molds have evolved to favor their relatives, which is predicted by kin selection theory," said Queller. "The exact behavior cannot be extrapolated, because the way that slime molds favor relatives is different from what humans do, but it would not be surprising if kin selection has also produced humans that tend to favor their relatives."
Kin selection is the evolutionary theory that posits that individual organisms are more likely to help blood relatives because doing so increases the odds their shared genes will be transmitted to future generations. It's part of the reason parents instinctively protect their offspring (even at risk to themselves).
As human populations have expanded, social scientists say that kin selection - and resulting behaviors like altruism - expand from immediate family to clan to tribe to codified social custom and tradition.
GOOD FOR YOU - AND US
Like altruism, pride (one of the deadly sins) has long stymied scientific understanding. Some scientists, though, are making inroads.
Robins at UC Davis, with colleague Jessica Tracy, an assistant psychology professor at the University of British Columbia, have found that pride pretty much looks the same everywhere in the world, recognized by children as young as 4 and in all cultures, from Houston to isolated, preliterate tribes in Burkina Faso in West Africa.
If pride is a universal human trait, it must serve some sort of common purpose, Robins and Tracy speculated. To explore this idea, they asked diverse peoples for words associated with pride. The answers tended to describe two basic kinds of pride: "authentic" and "hubristic."
"Authentic pride is experienced when people succeed at something they've put a lot of effort into, and it's accompanied by feelings of confidence, accomplishment and productivity," said Tracy. "People who feel this kind of pride tend to be agreeable, extroverted and conscientious, with high self-esteem.
"In contrast, hubristic pride is more likely to occur when people attribute their success to something stable about themselves - like their ability - rather than their effort. It's accompanied by feelings of egotism and arrogance, and people who experience it tend to be disagreeable, aggressive, hostile, narcissistic and prone to shame."
Robins and Tracy hypothesize that pride evolved in early humans as a way to encourage good behavior and promote social well-being.
"The positive feelings of pride motivate people to engage in behaviors that are socially valued (i.e., good for the group), just as the feeling of joy motivates people to continue doing whatever it is that is making them happy, or the feeling of fear motivates them to avoid or move away from whatever it is that is making them afraid," said Robins.
Expressions of pride communicate to others that an individual has done something socially valued. Cues like a puffed-out chest or strutting about say, "Look at me, I did something great and you should all give me more status and resources because I just helped out the group."
Hubristic pride may simply be the cheater's version, allowing individuals to garner social esteem and reward without actually doing the work.
CULTURAL EVOLUTION
When the Human Genome Project was concluded in 2003, some scientists and observers voiced renewed fears of a rise in "biological determinism," the persistent idea that humans can purposefully redesign themselves to be smarter, stronger or better-looking through gene manipulation.
That hasn't happened, and, according to Larry Arnhart, a professor of political science at Northern Illinois University, it never will. Writing in his book "Darwinian Natural Right" (State University of New York, $19.99), Arnhart says human nature is just too multifaceted, consisting of at least 20 desires shared by every human society throughout history.
Among them: sexual identity, familial bonding, social ranking, beauty, wealth, aesthetic pleasure, religious understanding and intellectual understanding."
Biotechnology isn't up to the task of permanently altering human nature. It doesn't address, for example, the other part of the equation: the environment.
"Genes, including the genes that make culture possible and that bias our decisions about what culture to adopt, are supremely important," said Peter J. Richerson, a professor of environmental science and policy and co-author of "Not By Genes Alone" (University of Chicago Press, $20).
"But that said, cultural variation far outstrips genetic variation and probably has for the last 100,000 years or more."
Prudentius was wrong to suggest human nature was solely an internal struggle. The fight is all around us, too.
Just look at modern Americans' widening waistlines, which could be viewed as ever-expanding evidence of our gluttony. Early humans were hunters and gatherers. Their bodies (and ours) evolved to cope with inevitable periods of famine by packing on fat when times were good. The invention of agriculture and the steady abundance of nutrient-rich foods have altered the equation. Our genes haven't changed as much as our jeans.
Any improvement in the situation will likely require a fundamental change in our behavior - and maybe a few mutating genes.
