A verbal essay is all it is!!!
So 1st you want to focus on environmental (nurture) development.
One example is how behaviour for instance can be environmentally changed by how people around the subject interact with them.
Then take a few scientific examples of nature and genetics, for example:
Tests have been run on identical twins to see if their tastes for food were the same or different, and the results showed that the tastes for food of identical twins were the same.
Then go on to say your own opinion on it all, and explain how you believe it works.
To finish just do a conclusion.
(basically it is just a verbal essay, you lay it out the same just saying it aloud)
P.S. Don't worry about how long it is, it's about quality NOT quantity!
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Oh yeah, just go with your idea! If you make a decision and stick with it, in this scenario it would probably be better than chopping and changing.