We all knew that kid who got straight As in school. Who was always first with their hand up to answer the teacher's question. Who knew the times tables without having to sing the song.
Were they that smart because they were born gifted? Because they studied for six hours a night? Or maybe they were the great grandchild of Albert Einstein?
"Intelligence is a complex construct and the word intelligence means different things to different people," Professor Con Stough from the Swinburne Centre for Human Psychopharmacology at Swinburne University told HuffPost Australia.
"In Psychology, and historically, we often substitute the word 'intelligence' with 'IQ tests'. In fact, this is probably the answer that a layperson would also give you if asked about intelligence."
More than an IQ test
A quick history lesson:
"IQ tests were first developed (1905 by Binet and Simon) to identify children who were not doing very well in school. So they are designed to measure and correlate with scholastic performance. IQ tests to predict a wide variety of other important variables such as the type of job you may have, health outcomes, some aspects of job performance amongst many others," Stough said.
"More recently there has been a movement to broaden the definition of intelligence and some have started to consider constructs like emotional intelligence. This is a realisation that our cognitive processes are affected by our emotions.
"Some children, for instance, may have difficulties in managing emotions and this might impact on the scholastic performance. We also know people in the workplace, whilst showing high technical intelligence in their field, are unable to relate to others, show leadership and some are unable to manage their emotions. This has raised questions about what is 'intelligence'."
What determines our intelligence?
With all that in mind, do we get our smarts, both practical and emotional, from our parents?
"Intelligence is caused by both our genes and our environment. So nature and nurture. There have been many twin studies in psychology and a field called behavioural genetics that have measured IQ in both MZ and DZ twins in what is referred to as a classical twin study.
"MZ twins share 100 percent of their genome and DZ twins share 50 percent of their genome, so comparing how similar IQ scores are in DZ and MZ twins allows us to estimate the relative genetic contribution. These studies often conclude that around 70 percent of IQ is heritable and about 30 percent is due to environmental influences," Stough said.
However Stough points out that there are some problems with taking these findings at face value.
"The heritability statistic is a population statistic, not one that can be used individually to infer someone's genetic contribution to IQ or intelligence. This is the average contribution in a particular society in which the twin study was conducted.
"Another significant problem with the view that genetic contribution is high is that we know that genes do not work randomly by themselves. They operate in an environment -- they get turned on and off depending on what is happening in the environment."
"More modern day behavioural geneticists have been using molecular genetics to search for the genes for intelligence. In my view that has been a spectacular waste of time, money and resources. Almost nothing in terms of genes have been identified that contribute to our intelligence," Stough said.
"In my opinion this is because a better way to understand our intelligence is to understand how our genes and environment work together. When do genes get turned on and why? How can the environment interact with our genome to facilitate learning?
"Think of the height of wheat, which many assert is 100 percent genetically determined. If we don't water the seeds then it will not grow at all. Changing the environment in clever ways could potentially enhance the function of our genes or even lower their contribution. There is much to learn yet."
A sum of many factors
So now we know how intelligent we are comes down to our genes as well as our environment. But it doesn't stop there. Stough points out that someone's socioeconomic status also plays a (debatable) part.
"Socioeconomic status is a very interesting side issue. Many Intelligence researchers argue that socioeconomic status is caused by our genes. Higher socioeconomic status is caused by better genes. Better genes contribute to better ability to compete in our society for things such as income, jobs, health and private schools," Stough said.
"I don't accept this belief -- certainly IQ predicts many of these outcomes, but I believe that environment, possibly over many generations, can cause socioeconomic status, which in turn predicts outcomes in schools, education and job prospects."
On top of those factors you need to consider diet, sleep and exercise as well as mental health.
"We are studying nutrition at Swinburne, but we know that health and brain function, exercise, sleep, quality of education and many other environmental factors are also contributors [to intelligence]. For instance, poor mental health (anxiety, depression, ADHD etc) will make it almost impossible for a child to concentrate and maximise his or her learning opportunities."
"Poor diet, lack of sleep, illicit drugs and poor health will also lead to poorer outcomes for learning and attainment. Poor school outcomes leads to poorer job opportunities and to lower socioeconomic status."
"At Swinburne we are also developing emotional intelligence in children and adolescents. We believe that this type of intelligence is important for life outcomes, mental health and happiness," Stought said.
"Helping children and adolescents understand their own emotions, form better relationships and manage negative emotions are a series of fundamental skills for life and for showing 'intelligence'.
"How all of these factors interact with our genes is also an important next step. We are at the beginning of this journey."
What can be done
In order to offer a child the best possible chance at optimum intelligence we need to start early, and we need to take a multi-pronged approach.
"We need to tackle all of these environmental issues as early as possible. We need to provide better environments for all children and adolescents. We need to find learning methods that stimulate interest in all children with different personalities and learning styles," Stough said.
"We need to better develop teachers and schools. We need to help parents understand the importance of diet, exercise, sleep, education and emotional intelligence.
"Parents have a role. Schools have a role. Teachers can prevent students from learning by not providing the most conducive environment, so schools are important. We know even peer groups are important. Diet can lead to poorer outcomes and so can sleep or no exercise.
"Sometimes the limits we impose on our children and on ourselves could limit the development of our intelligence. At Swinburne we also believe that poor emotional intelligence can also limit, much like many mental and non-mental illnesses can impair our ability to learn and therefore our intelligence.
"Remember that IQ tests were developed to measure educational attainment, so anything that prevents us from learning technically impairs our intelligence."