Truce crumbles

• CNN crew sees protesters fall, some carried out on stretchers


• European diplomats are to land in Kiev to push for peace


• Ukraine's president declared a truce and the start of negotiations the night before

Are you in Ukraine? Send us your photos and experiences but please stay safe.

Kiev, Ukraine (CNN) -- A shaky truce crumbled in Kiev on Thursday morning, when gunfire erupted at Maidan, or Independence Square, which has been ground zero for anti-government protesters.

It is unclear what prompted the gunfire. But CNN crews at the scene reported that as security forces were moving away from the area, a group of protesters pursued them.

When the bullets flew, several demonstrators fell to the ground. At least three people were carried away in stretchers. It was unclear whether they were dead or wounded.

Shortly afterward, security forces appeared to withdraw, leaving the tent city once again in the hands of protesters.

Thursday's violent developments came just hours after embattled President Viktor Yanukovych announced a truce -- and opposition leaders had agreed to abide by.

Later Thursday, European foreign ministers will hold an emergency meeting in Brussels, while three of them will go to Ukraine to do diplomatic triage.

Opposition leader Vitali Klitschko, a former world-class boxer, is expected to sit down once again Thursday with Yanukovych. Their meeting Wednesday led to the truce.

No one wanted to see a repeat of Tuesday's lethal violence and chaotic clashes that left 28 dead, police and protesters alike. It was the deadliest day of protests, which began in November when Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.

Dissatisfaction with the decision morphed into resentment of Yanukovych's closeness to Russia and an attack on his base of power. The protesters demand changes to the constitution that would hand some of it to the parliament.

The unrest has intensified after an anti-protest law went into effect. Throngs of demonstrators took to the streets to decry the law.

iReport: Protester describing bloodied people being rushed to medics

CNN's Nick Paton Walsh and Phil Black reported from Kiev, while CNN's Ben Brumfield reported and wrote from Atlanta.

See what comes out of exploding star

NASA's NuSTAR telescope array generated the first map of radioactivity in the remnants of an exploding star, or supernova. Blue in this image of Cassiopeia A represents radioactive material. Click through to see other wonders of the universe.

A supernova was spotted on January 21 in Messier 82, one of the nearest big galaxies. This wide view image was taken on January 22.

The M82 supernova, seen here, has been designated SN2014J because it is the 10th supernova detected in 2014. At 11.4 million light years from Earth, it is the closest Type Ia supernova recorded since systematic studies with telescopes began in the 1930s.

The Hubble Space Telescope is letting us see farther than ever into the universe. This long-exposure image is the deepest-ever picture taken of a cluster of galaxies called Abell 2744.

Is that a giant hand waving at us? Actually, it's what's left of a star that died and exploded a long time ago. Astronomers nicknamed it the "Hand of God." NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, took this image in high-energy X-rays, shown in blue. The image was combined with images from another space telescope, the Chandra X-ray Observatory.

The Hubble Space Telescope captured this image of the Southern Pinwheel Galaxy, one of the largest and closest galaxies of its kind. The center of the galaxy is mysterious, researchers say, because it has a double nucleus -- a supermassive black hole that may be ringed by a lopsided disc of stars, giving it the appearance of a dual core.

Hubble scientists say this is the best-ever view of the Tarantula Nebula, which is located in one of our closest galactic neighbors, the Large Magellanic Cloud.

Those spots on our sun appear small, but even a moderate-sized spot is about as big as Earth. They occur when strong magnetic fields poke through the sun's surface and let the area cool in comparison to the surrounding area.

This Hubble image looks a floating marble or a maybe a giant, disembodied eye. But it's actually a nebula with a giant star at its center. Scientists think the star used to be 20 times more massive than our sun, but it's dying and is destined to go supernova.

• Astronomers have mapped the radioactive material from a supernova


• The supernova explosion happened 11,000 light years away


• Heavy elements such as gold and calcium come from supernovas

(CNN) -- Cassiopeia A was a star more than eight times the mass of our sun before it exploded in the cataclysmic, fiery death astronomers call a supernova.

And thanks to NASA space telescopes, scientists are learning more than ever about exactly how it happened.

The NuSTAR space telescope array is the first to map the radioactive material from a supernova explosion. The results were published Wednesday in the journal Nature.

"Until we had NuSTAR, we couldn't see down to the core of the explosion," Brian Grefenstette, lead author and research scientist at the California Institute of Technology, said at a news conference Wednesday.

NuSTAR's observations of Cassiopeia A showed scientists the location and distribution of radioactive titanium-44, an unstable isotope with a half-life of about 60 years. The supernova explosion's light arrived on Earth about 350 years ago, but even today there's still plenty of titanium-44 to be observed.

Each atom of titanium-44 decays to calcium, as well as two particles of light at particular frequencies that NuSTAR can detect. NuSTAR, which stands for Nuclear Spectroscopic Telescope Array, launched in June 2012 and consists of an instrument with two telescopes that focus high energy X-ray light.

There's currently no solid model for how the supernova explosion process actually works, Grefenstette said. Scientists would like to know more, especially because the components of our planet came from a supernova that blew up about 5 billion years ago.

"People should care about supernova explosions because that's where all the stuff that makes us comes from," Grefenstette told CNN. "All of the iron in your blood and calcium in your bones and teeth, and gold in your wedding band, that all comes from the center of a supernova explosion."

When stars collide ... we get gold?

All the world's gold came from collisions of dead stars, scientists say

The map of the radioactive ash that NuSTAR studied is akin to a "fossil record," Grefenstette said. It is an imprint of what happened in the explosion, and it is helping astronomers rule out previous ideas about how stars explode.

So here's what scientists think is happening: At the center of the supernova, an intense amount of pressure builds up. Neutrinos, tiny particles, are produced and heat up the gas in the center.

"What you get is just like when you're boiling water on your stove top: You get hot bubbles at the bottom that try to rise up through the cold material above it, and the whole thing starts to slosh around," Grefenstette said.

Big "bubbles" form in this process, and the whole thing starts to fall apart, he said.

"It's like blowing the top off a pressure cooker, and the shock wave rips apart the star," Grefenstette said at the news conference.

The NuSTAR observations suggest that these large bubbles are present at the center of the star, a phenomenon that had been thought about through computer models but never observed.

The new study finds evidence for the bubbles forming in the first fraction of a second of the explosion.

"It's like you blink your eyes twice, and the whole thing has exploded, and we're seeing it three or four hundred years later, preserved in the radioactive ash," Grefenstette said.

Researchers describe this explosion process as "asymmetrical" because according to their modeling, temperatures and densities must be different around the explosion in order for the "bubbles" to escape and let the shock wave out.

Scientists aren't ready to say definitively that this "sloshing" model of supernova explosion caused Cassiopeia A to blow apart, but the evidence supports that theory, Grefenstette said.

Cassiopeia A, a well-studied celestial object, is about 11,000 light years away. That means technically, it exploded more than 11,000 years ago, but because of its distance from us, we only could have learned about it about 350 years ago.

It's unlikely that any Earthlings observed it back in the 17th century, however, because of the amount of dust between our planet and the supernova explosion. There is a record of a new star charted by a British astronomer around the time the supernova's light should have reached us, but it's controversial, because that star is not in the place in the sky where Cassiopeia A would have been.

The Hubble Space Telescope has examined the supernova's optical light, and the Chandra X-ray Observatory looked at its low-energy X-rays. The radioactive ash is available for the first time to NuSTAR, which can detect high-energy X-rays.

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NuSTAR has also given scientists a new mystery to ponder about supernovas. They expected the radioactive titanium map to match the map of iron, because those elements are thought to have been created in the same place of the explosion. Instead, their distributions are very different.

This may mean that that there is more iron that hasn't been seen yet or that there is something completely different that generates elements.

"NuSTAR is living up to its name way in two ways," Robert Kirshner, an astronomer at the Harvard-Smithsonian Center for Astrophysics who was not involved in the study, said at the news conference. "It's not just nuclear, but it's new."

Cosmic wow, a rare exploding star!

Facebook acquires WhatsApp for $19 billion

FACEBOOK has bought WhatsApp for $19 billion in cash, stock and shares.

In their biggest acquisition to date, Facebook has taken on the popular text messaging system, which is used by more than 450 million people.

Although many younger people are drifting away from Facebook, WhatsApp is rapidly increasing in popularity. In some markets it is now more prominent than Facebook, with approximately one million new users a day.

Mark Zuckerberg, Facebook founder and Chief Executive Officer, wrote on his Facebook page: “WhatsApp will complement our existing chat and messaging services to provide new tools for our community”.

WhatsApp founders Jan Koum and Brian Action are now to join the billionaire set in Silicon Valley. The deal includes $4 billion in cash, $12 billion in Facebook shares and a further $3 billion in stock at a later date.

In 2012 Facebook purchased Instagram for $1 billion, which had been their largest purchase to date before the new deal with WhatsApp.

It's not 'stand your ground,' it's race

• Mark O'Mara: "Stand your ground" eliminates duty to retreat from a threatening situation


• He says according to testimony in two Florida cases, retreat wasn't perceived as an option


• O'Mara: "Stand your ground" should be removed from jury instructions to avoid confusion


• He says we need to deal as a society with how race affects perceptions

(CNN) -- There has been a lot of debate about Florida's "stand your ground" law in recent days. From my perspective, the George Zimmerman and Michael Dunn cases were not "stand your ground" cases, although I know reasonable people disagree about my stance on this.

What I think most people can agree on is that the "stand your ground" law is confusing. I know because I've tried to explain it a hundred times. And here is my 101st attempt, this time in the context of the hung jury on the murder charge in the Dunn trial.

When you hear "stand your ground," think "no duty to retreat." For centuries, traditional self-defense implied a duty to retreat, meaning when someone finds himself in a threatening situation, he has a duty to exhaust all viable options to retreat before resorting to deadly force.

The problem with the duty to retreat is that, in the cold light of day, jurors may have a better perspective on a person's options to retreat than the person had during his life-threatening encounter.

Because of concern over this Monday morning quarterbacking -- and with the thought that we were sending people to jail who were otherwise justified in using deadly force -- legislatures in many states modified their justifiable use of force laws to say that people who have a reasonable fear of imminent great bodily harm or death very affirmatively DO NOT have a duty to retreat.

In other words, they can "stand their ground" and meet force with force, including deadly force. "Stand your ground" refers specifically to the removal of the duty to retreat.

In a self-defense scenario where imminent harm is so immediate that retreat is not possible, there is no "duty to retreat" to waive, and therefore "stand your ground" does not apply.

Is Dunn verdict Zimmerman?

According to evidence presented at his trial, at which I represented him, George Zimmerman was on the ground, being beaten, when he pulled the trigger; he had no way to retreat, and it was not "stand your ground."

Michael Dunn, if we are to believe his story, thought Jordan Davis had a shotgun; there is no retreating from a shotgun at short range, and therefore it was, arguably, not "stand your ground."

If we repealed "stand your ground" laws tomorrow -- if we reinstated the duty to retreat -- George Zimmerman still gets an acquittal, and the Dunn jury still hangs.

The underlying concern with the statute is that those who are aware of it may be emboldened by its protection, and place themselves in, or remain in, a circumstance that increases the likelihood of using force.

A concern with the national focus on these two recent cases is that the concept of "stand your ground" has been misperceived by so many that there are now those who believe use of deadly force is more justified than it is, and there are those who believe that it is intentionally used to kill minorities.

Even if unintended when enacted, "stand your ground" suffers from enormous misunderstanding and, consequently, mistrust.

People who think I'm wrong and who argue that Zimmerman and Dunn are, in fact, "stand your ground" cases often point out that the "stand your ground" language from the statute appears in the jury instructions. It does. There's a lot of language from Florida's justifiable use of force statute that shows up in the jury instructions, and in any given self-defense case, much of it doesn't apply to the details presented in court. I think this is why juries -- and not just Florida juries -- find deliberating self-defense cases so challenging.

There is a simple solution: I think we should remove the instructions about "no duty to retreat" in any self-defense case where the facts don't support it.

After defending the Zimmerman case, and after providing in-depth commentary on the Dunn trial, I've discovered that when people say they have a problem with the "stand your ground" law, it's not really the "no duty to retreat" aspect of our self-defense laws that gets them upset.

What causes people to be upset is the concept of "reasonable fear" and how subjective it is. In effect, it is possible for someone to believe they are justified in killing another human being -- that they have reasonable fear -- even if that fear turns out to be unwarranted in the cold light of review.

The standard is, and has to be this: Was that fear reasonable under the circumstances? This has been the standard for determining self-defense for centuries, and it has nothing to do with "stand your ground."

Repealing the "stand your ground" provision won't change the fact that sometimes self-defense homicides will be ruled justified based upon a technically unwarranted, but otherwise reasonable, fear.

The concerns that are voiced in this regard are more properly focused not on a law, (be it "stand your ground" or simple self-defense), but on the system that harbors subtle but undeniable biases toward certain demographics.

Where the discussion about the strange nuances of our self-defense laws becomes most disturbing is when you introduce race into the equation.

I think it is sufficiently established as a sociological fact that black men -- especially young black men -- are regarded by many people, of all races, as more suspicious and more threatening than men and women of other races. It's heartbreaking to think this is true, but it's folly to deny it. If young black men are regarded, in general, as more threatening, then some people may be more likely to manifest that fear -- however unwarranted in the individual case it may be -- and act on that fear, sometimes with deadly force.

When this element is added, the job of the jury includes trying to wade through whether these subtle biases (or justifications) for fear are present, and what weight to give them. Now, we are asking our juries to see deep into the heart of the citizen accused -- maybe too deep. Is it fear, or disdain? And how much of each?

It's outrageous that these tragedies occur, but repealing "stand your ground" laws will not stop them. The problem is not in our legislation, it's in our collective hearts. We have a system that is still, without question, the best in the world, but it's far from perfect.

It still, unfortunately, carries with it the inertia of more overt racial inequities from our recent past. As an example, while there are studies that support that the immunity afforded by "stand your ground" can produce racially disparate results, I contend the statute itself is race-neutral, and it is the inequitable application that evidences an inherent bias of the system.

But our self-defense laws are not the only laws applied with racial inequity. Look at the incarceration statistics in the United States: Black men are disproportionately represented by an extraordinarily wide margin for virtually every type of crime, from petty theft to drug charges to murder. Repealing laws against these crimes won't fix the problem of racial inequity in our justice system, just as repealing the "stand your ground" provisions will not either. Rather, the solutions lie in a more system-wide or society-wide approach.

We have a success in this area already. The recent changes to federal sentencing statutes to address the strong negative effect on blacks charged with certain crack cocaine charges shows that we can both acknowledge these disparities in application and change them.

In addition, the systemic biases are not simple to explain. While it is admitted that there is bias in the system, this does not fully explain the numbers. The black community must look not only to the system, but also to itself for answers to how and why young black males find themselves in the system in wildly disproportionate numbers.

There is no easy or quick solution. I am, however, encouraged for this reason: We, as a nation, have focused more energy, and have begun more discussion on these issues than I have ever witnessed. At least not since the days of my childhood, when I was too young to offer a voice to the conversation about civil rights, a conversation started by men I respected, men who, unfortunately, died too young. It takes courage, it turns out, to talk about race.

I believe that we can fix the problem of racial inequity in our justice system, but first we have to admit that the problem exists, and then we have to have the courage to engage in an open, honest and thoughtful conversation about the true state of race relations in America.

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The opinions expressed in this commentary are solely those of Mark O'Mara.

Passenger beaten aboard cruise ship

According to a criminal complaint, Ketut Pujayasa, 28, physically and sexually assaulted a female passenger while in international waters.

• Ketut Pujayasa, 28, is accused of physically and sexually assaulting a female passenger


• She managed to escape, but suffered injuries sufficient to have her moved to a hosptial


• Cruise line president says attack is believed to be the first of its kind in 140 years

(CNN) -- The fight started because of an alleged slight -- and ended with a crew member being accused of attempted murder.

Ketut Pujayasa, a 28-year-old room service attendant with Holland America's ms Nieuw Amsterdam, physically and sexually assaulted a female passenger while in international waters, according to a criminal complaint.

The 31-year-old woman, a U.S. citizen, was not identified in the complaint filed Monday in the U.S. District Court for the Southern District of Florida.

Pujayasa told authorities he delivered breakfast to the woman's room. He knocked three times before the passenger acknowledged him.

Outside the room, Pujayasa heard a female voice shout, "Wait a minute, son of a bitch!" according to the complaint. She later opened the door, and he left the food.

Pujayasa did not report the incident to a manager, but told authorities he found the woman's comment offensive. He returned to her room later. No one answered, and he left.

That same evening, he looked for the woman on a deck, "in order to punch her in the face for insulting him that morning," the complaint read. He left after realizing the location was too crowded.

That night, Pujayasa returned to the passenger's room and used his master key to enter.

He is accused of choking and punching the woman with whatever was available -- a laptop, a curling iron. She fought back with a cork screw.

At one point, the fight moved onto a balcony, where Pujayasa tried to push the woman overboard, the complaint read.

She eventually was able to break free and ran from her room. Another passenger rendered aid.

Due to the severity of her injuries, the woman was transported via air ambulance to a hospital in Florida after the ship docked the next morning. Her condition was not immediately clear.

According to the complaint, Pujayasa returned to his room after the attack and told his roommate to contact ship security because he had killed a passenger. He was placed under guard on the ship.

Pujayasa, a citizen of Indonesia, was hired in 2012 following a screening that included a clean criminal history check, the cruise line said in a statement. He had no performance issues and came with good references.

Attempts to contact his attorney Tuesday were unsuccessful.

"At Holland America Line, the safety of our guests is our highest priority, and we are shocked and deeply saddened by this incident," said Stein Kruse, president and CEO. "To our knowledge, no incident like this has occurred in our company's 140-year history."

CNN's Suzanne Presto contributed to this report.

Soldier who killed Iraqi family kills self

Former Army soldier Steven D. Green was convicted five years ago of raping a 14-year-old Iraqi girl and murdering her and her family.

• Steven Green was found in his cell on Thursday and died two days later


• A medical examiner ruled his death suicide by hanging


• In 2006, Green and four others raped a 14-year-old Iraqi girl and killed some of her family


• He was sentenced to multiple life terms in federal court because he had left the Army

(CNN) -- A former U.S. soldier convicted five years ago of murdering an Iraqi family died Saturday, two days after an apparent suicide attempt in his Arizona prison cell, authorities said.

Steven Green was found unresponsive last Thursday, according to the Federal Bureau of Prisons.

The deputy chief medical examiner with Pima County, Dr. Eric Peters, said the cause of death was suicide by hanging.

In 2009, Green was found guilty in U.S. District Court in Kentucky of raping a 14-year-old Iraqi girl and murdering her, her parents and her 6-year-old sister in the town of Yusufiya, about 20 miles south of Baghdad. The crimes occurred three years before the conviction.

Prosecutors sought the death penalty but a jury couldn't reach a unanimous decision.

He issued a public apology for his crimes, one the relatives of the victims didn't accept.

Green, who was sentenced to multiple life sentences without possibility of parole, told the family he was "truly sorry for what I did in Iraq."

"I helped to destroy a family and end the lives of four of my fellow human beings, and I wish that I could take it back, but I cannot," Green said, reading a statement at a victim impact hearing. "And, as inadequate as this apology is, it is all I can give you."

The relatives decried Green's sentence and testified about how the heinous crime had shattered their lives, and how it will haunt them always.

Green said that he knew "you wish I was dead, and I do not hold that against you. If I was in your place, I am convinced beyond any doubt that I would feel the same way."

Green was tried in a civilian court in Paducah, Kentucky, because he had already been discharged from the Army by the time his crimes surfaced.

He was the last of five soldiers who served in the 101st Airborne Division, based at Fort Campbell, Kentucky, to be convicted for the crimes and their subsequent cover-up.

From 2009: Steven Green: 'You probably think I'm a monster'

CNN's Dave Alsup contributed to this report.

What your IQ score doesn't tell you

• IQ is a measure of your reasoning and problem-solving abilities


• Your score reflects how well you did on a series of tests compared with others your age


• Your IQ can change over time, and scores have improved between generations


• Having a high IQ is not a guarantee of success, experts say

(CNN) -- Three-year-old Alexis Martin reads at a fifth-grade level. She taught herself fluent Spanish using her parents' iPad.

"From 12 to 18 months old, we'd be driving around in the car, and she would recite her bedtime story from the night before," her dad, Ian, told CNN affiliate KNXV. "She didn't just recite them; she recited them exactly."

Alexis is the youngest member of Arizona's Mensa chapter. American Mensa (PDF) is an organization for people with IQs in the top 2%. The average IQ is 100. Martin's tops 160.

Mensa has more than 55,000 members nationally. You'd probably recognize some of the more famous ones: Nolan Gould, who plays Luke on ABC's "Modern Family"; Richard Bolles, the author of "What Color is Your Parachute?"; the Blue Power Ranger (OK, he's a fictional member).

But what does an IQ score really tell us about a person? Will Alexis be a genius for life? And if you still can't speak Spanish at age 50, should you just give up?

What your IQ score means

An Intelligence Quotient, or IQ, is a measure of what psychologists call our "fluid and crystallized intelligence." Put simply, an IQ test measures your reasoning and problem-solving abilities.

There are different kinds of IQ tests, but most analyze your visual, mathematical and language abilities as well as your memory and information processing speed. A licensed psychologist administers a series of subtests; the results are then combined into one score: your IQ.

"Anybody with very high IQ, they have the ability to manipulate, process and interpret information at a deeper level and a higher speed than the average person," explained Mensa's gifted youth specialist, Lisa Van Gemert.

What your specific numerical score means depends on the test you take. IQ is really a measure of how well you do on a test compared with other people your age.

Scores are generally shown on a bell curve. The average score is 100. People to the far left or far right of the curve are outliers. Alexis, for example, is on the far right of the curve for children her age.

Bleacher Report: How smart are you? Take the Wonderlic test and find out

What it doesn't mean

"The difficulty with these kinds of tests is that they're a snapshot," Van Gemert said. "We see what the kid looks like on this day, on this particular test, with this particular tester."

An IQ score doesn't measure your practical intelligence: knowing how to make things work, says Richard Nisbett, a professor of psychology at the University of Michigan. It doesn't measure your creativity. It doesn't measure your curiosity.

It doesn't tell your parents or teachers about your emotional readiness. Maybe as a 5-year-old, you can read and understand The Economist. But are you prepared to deal with stories about war-torn countries or prisoners on death row?

It would be a mistake, Van Gemert says, to look at a child with a high IQ as nothing more than a brain. Like any trait -- blue eyes, big feet -- their IQ is just one part of who they are.

Your IQ can change over time

A lot of factors can affect your IQ score over time. Poverty. Nutrition. Stress. How familiar you are with standardized tests. Nisbett's research has shown that children from lower socioeconomic levels adopted into a middle-class family often increase their IQ scores by 15 to 20 points.

"Heritability is not as great as some people (believe)," Nisbett said. "Environmental factors are very potent."

In one study, researchers tested 33 adolescents' intelligence once and then again four years later. In that short amount of time, some of their IQ scores varied by more than 20 points. The changes matched with structural and functional changes in their brains.

Kids who are geniuses at age 2 rarely stay that way, experts say. It's easier, Van Gemert explains, for young children to distinguish themselves on the curve.

In other words, it's easy to spot a genius 3-year-old when she's reading at a fifth-grade level and speaks fluent Spanish. But what makes one 47-year-old more intelligent than another? Is it education? Life experience? Their ability to put together a piece of furniture from IKEA?

You're smarter than your ancestors

Since the early 1990s, when IQ tests were first standardized, researchers have seen substantial increases in IQ scores with each passing generation. So the average 10-year-old today would score higher on the same test than a 10-year-old from 1954.

This doesn't mean we necessarily have bigger brains than our great-great-grandfathers; it just means we've improved our abilities to think logically, solve problems and/or use our abilities in hypothetical situations.

It's known as the Flynn Effect, for moral philosopher James Flynn.

"The cars that people drove in 1900 have altered because the roads are better and because of technology," Flynn said in a TED Talk last year. "And our minds have altered, too. We've gone from people who confronted a concrete world and analyzed that world primarily in terms of how much it would benefit them to people who confront a very complex world."

For instance, education has changed. We've learned to classify the world, to compare groups like animals or modes of transportation, Flynn said. We've also been taught to accept hypothetical situations (you remember algebra, right?). Our ancestors dealt only with what was right in front of them.

Our jobs have also changed. In the early 1900s, only 3% of Americans had professions that were "cognitively demanding," Flynn said. Today, 35% of us do. As such we're used to solving complex, hypothetical problems, like the ones on an IQ test.

Health factors may have had an influence as well. Studies have shown that early childhood immunization rates are a big predictor of a nation's average IQ score. So decreasing infectious diseases worldwide may have attributed to the overall increase in subsequent generations' IQ scores.

"From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks," the authors of one study wrote.

Not a genius? Don't panic

You probably remember the dreaded SAT or ACT test you took in high school. That's a type of IQ test. But Nisbett believes that a student's grade-point average is a better predictor of their success than their test scores.

"GPA is raw smarts times how hard you work times self-control times a lot of other things. That's true for success in life," he said. "I see graduate students with extremely high IQs who can't achieve much because they're lacking in curiosity. ...They're lacking the ability to get along with people."

Having a high IQ is not a guarantee of success, Van Gemert agrees, just as having a lower IQ is not a guarantee of failure. Good habits, perseverance and a strong work ethic are just as important as intelligence.

"If you don't develop those other qualities, you can waste a smart IQ," she said.

Van Gemert recommends that parents view their homes as a petri dish, one where they're trying to grow their children. That means lots of time spent together, interacting, and lots of books, building blocks and board games.

"The most important thing we can do for kids is to play with them," she said.