Why are we the way that we are? It’s a question we ask ourselves often, and one we are also asked by others when we do something spectacular, or spectacularly awful – usually the later, expand=1] if we’re being honest.

This week on #TuesdaysWithBill, young Padawan Evan would like to know whether physical traits are determined mostly by genes or mostly by external factors such as nutrition and exercise. And ideally, Evan wants an answer in percentage form. Why? Because he is arguing about this with his mom, and nothing settles a Tuesday afternoon family feud like cold, hard numerals.

Bill Nye chooses the path of diplomacy here, not because it’s the right thing to do, but because it is currently impossible to determine to what extent our physical characteristics are the result of nature or nurture. Nye cites the example of height, and looks back to the origins of all humans: Africa. In Africa there are tribes that are very short where food is scarce, and conversely those that are very tall where food is abundant. The expression of our genes is this case is certainly very much controlled by external factors, and it’s fascinating. The further back archaeologists dig, they find shorter and shorter skeletons; proof that our increased food supply and nutritional access has given the modern human a real height booster, especially since the industrial revolution.

If you go searching through science journals, you’ll find papers that examine individual traits, and for some the conclusion is nurture, and for others it’s nature, so as a whole the reality probably resides in the middle ground, as a combination of all factors. Some papers even argue that personality and intelligence traits are entirely environmental, but there are contradicting views on this. So make peace with your mother, Evan. You probably got your curious mind from her. Or did you?

Bill Nye’s most recent book is Unstoppable: Harnessing Science to Change the World.

Evan: Hi Bill. My name is Evan. I am 16 years old. Here's my question for you, are physical traits such as height determined mostly by genes or by nutrition and exercise? Give me a percentage number. My mom and I are having an argument over this and I heavily believe that it's more of the genes that contribute to this trait such as height. Thank you.

Bill Nye: Evan, that's a great question. The right answer is clearly both. So, some people are genetically predisposed to be tall as you point out, but I can tell you people in the West, like in our civilization here in the United States and Canada, are getting taller; offspring are growing taller and taller and that is almost certainly do to improved nutrition. And archaeologists who love this stuff go digging up old graves in big cities and they find that people in the 1700s and the 18th century were not as tall as their descendants are today. And this is almost certainly a result of nutrition. So it's both. Furthermore, it's something that just fascinates me. In Africa - all of our ancestors are ultimately from Africa. And Africa you find indigenous people, tribes who have lived there for millennia that are both very tall where food is abundant and there's other tribes that are not especially tall where food is harder to get. And it's fascinating. Right there to this day you can find where the environment, the evolutionary pressure to find nutrition, to find food has affected the success of offspring. If you're too tall and there's not enough food around you can't feed yourself and so you don't have kids. If on the other hand you live where food is abundant, fruit is growing on trees, as the saying goes, you can be taller and be just ultimately a bigger animal in the same forest, in the same jungle and just be more successful. So the answer is both. You've got to eat breakfast. I'll leave you with that. If you don't eat breakfast you're just not going to be as successful in life.