Seeing that this topic is the essence of much in way of research and thought, divergent answers will be the norm here. I think that you will need to sort through much out there. In my own mind, I think that the environmental factors that surround one as they grow up and mature play a vital role in determining their understanding of themselves and the world in it. Genetics do have a role, but social conditions and cultural capital, in my mind, are more essential in the process of gaining understanding about themselves. It seems to me that the setting in which one grows is important to controlling how one interprets and acts on information. The question's parameters of intelligence might need to be refined a bit, as well.
Of course, both are important, but if I had to argue for one, I would say that generally speaking environment is more important. I would give several reasons for this. First, we are all social beings and our environment affects us more that we can ever imagine. Peter Berger, the great sociologist has shown this in several different ways. Our perceptions, categories of thought, commonsense are all shaped by your surroundings. So, if the surrounds are good, then it will help develop an individual in many different ways. Second, a good environment can compensate for average genetics. There are many average people genetically speaking that learn to be intelligent through hard work and good education.
In the most simple terms of definition for intelligence, I could argue that much of the potential for intelligences are innate - we are born with it. But as a teacher, I have time and again come across the brightest of students whose intelligence was never nurtured nor developed. Only the right environment, from nutrition to socialization, from parenting to safety, from language acquisition to higher education can bring a person's intelligence into full bloom.
But I agree with what has been argued here about intelligence being nearly impossible to define. There is simply hundreds of ways intelligence can be both measured and expressed, and many intelligences that are completely misunderstood.
I think you have to be very careful to define what you are talking about when you discuss this type of question. I would think of intelligence as your potential for learning. Both genetics and environment are important for the expression of that potential. Genetics kinds of puts an upper limit on what you might be able to achieve; what you do achieve depends on the experiences you are exposed to, your opportunities, the expectations you and others have for you...all kinds of intangibles. I have students who are quite intelligent, but for whatever reasons, don't expect to do well in school--so they don't. I have others that work SO hard that they do far better than would be predicted on the basis of their IQ
First of all, if you are going to answer this question, you must define what you mean by intelligence. That, in itself, is an almost impossible thing to define.
I myself am not sure how to define intelligence. But if I had to answer this question, I would say that environment plays a greater role in how intelligent a person ends up seeming (except for extreme cases such as clearly disabled people).
If a person is surrounded from childhood by books and discussions of current events and science projects and such, they will surely seem more intelligent because they will be more used to thinking and more exposed to ideas.
In regards to intelligence, the environment plays the most important role. Both are very important, but I believe that intelligence is relative to the expectations of a culture. In some cultures being book smart would make a person appear dumb while the ability to hunt and provide through one's own skills is considered highly intelligent.
The other reason why I feel environment is so significant is that a child who has a high IQ but is kept boarded up and not allowed to communicate with others and does not develop language by 5 to six years old usually will not develop language as most people use it.
In addition, I have raised foster children with lower IQ's who once placed in a supportive environment have gone on to attend and complete college when people thought they would not even make it through high school.
As a teacher I have been taught that the students who learn to read best are the students who have books in the home and who interact with reading with their parents or caregivers. The home situation makes a difference in the development of children.