For those of you with a little science background, do you remember the Lamarckian theory of how traits developed? It was like this: a giraffe finds itself doing well in a habitat where the best and most plentiful food for it is in trees, specifically the leaves. So, the giraffe stretches for the leaves and can reach a few. The continued neck stretching has tends to develop a bit longer neck which is then passed on to his kids. Likewise, these kids stretch for higher leaves and eventually, a few years down the line, we have the modern giraffe with the long neck.
This is called soft inheritance. It means that if I read a lot, I will pass along more reading/comprehension ability to my child. If I spend time in the gym developing biceps, I will pass along a tendency for my child to have stronger biceps. Kind of like Darwin, except that the changes are not coded in a hard way and then, over time, weeded out by nature, but rather acquired through life experience.
According to Darwin, the taller giraffes were more able to get leaves and thus more able to live. They were more fit for their environment. That, in turn, meant that they were more able to reproduce other giraffes kind of like them and over generations the giraffe gets taller. We all know that Darwin won that argument, right?
Well, yes. But it is more complicated. In the past 40 years another factor has come to light, only really studied for the past 20. Superficially it seems like Lamarckism. What it is more accurately described as is life experience turning certain genes on and off and these new switches often passing to offspring. And, it is a theory with very rigorous proofs and observations behind it, quite as solid scientifically as what Darwin brought us.
For example, the Nova episode below shows lab rats raised by “licking” mothers, mothers who lick the babies and give them attention, lab rats that grow up to be cuddly and sociable. Non-licking moms raise anti-social rats. It can be shown that these tendencies are created by the experience by swapping litters at birth. The non-licking moms raising offspring of licking moms raise unsociable little characters. The licking moms getting the offspring of the non-lickers, raise sociable pups.
This is the real zinger. They discovered what the switches were, and seeing precisely what they were, they gave non-social rats one single shot from a hypodermic designed specifically to erase these switches and … voila, the rats became sociable! After one shot! AND THE CHANGE WAS PERMANENT!
That is only one of the things shown through epigenetics. The Nova show also shows how the diet of your grandparents can skip health effects on your parents and affect YOU. Chew on that for a bit.
That is why I said that the “Nature vs. Nurture” idea was more complex than most people think. I leave you to enjoy your own research of epigenetics.
For further study (the first in the list from Nova is my favorite):