"I believe that in the nature vs. nurture debate, that nature dictates 51% of a person's behaviour while nurture only influences 49% of the behaviour". Is it true
I think environment (nurture) plays a bigger influence. Although our genetics are important to our development as individuals, it is how we are raised and the experiences we have that truly make us who we are. There is no substitute for a solid, loving family situation when one is young. Even if siblings seem to have things in common, remember they share environment and genetics.
I wouldn't have any trouble accepting your percentages, but then again I wouldn't have any trouble accepting a lot of different percentages either. I don't think it's knowable and I don't think it needs to be known. It's enough to know that both are important.
If pressed, I would lean a little more to the nurture side. I think nurture can mold nature more than nature can overcome nurture. But not everytime. How's that for a firm stand?
I think the jury is still out on this one.
Maybe the best way to pose the question is to ask for opinions, as the question is currently phrased here, but part of me thinks that there may actually be a psycho-scientific answer. One day there may be conclusive evidence (and enough exhaustive study) to put a percentage on the degree of behavior governed by nature vs. the degree of behavior governed by nurture...but that evidence is still in abatement.
My experience suggests that nature does play a large role (in suprising areas) in the formation of our eventual personalities. It may also be worthwhile pointing out that humans are constantly adapting and changing so that there may be a greater propensity for nature to rule at some ages and nurture at others and there may also be an extremely complex set of forces at work which will complicate efforts to come to a firm answer to this question.
I do not think that there is any way to realistically put such a fine percentage on the amount of a person's behavior that is caused by nature or nurture. However, the basic idea of the quote seems sound. It seems likely that nature and nurture have roughly equal amounts of impact on how we behave.