I recently read an interesting article that brought attention the "Blood Type Diet," created by naturopath Peter J. D'Adamo.
Now, I have not personally participated in it, but I thought the proposed concept was fascinating. The methodology behind it is pretty simple; live a lifestyle that best fits the foundation of your DNA.
For example, persons with the blood type O are considered the descendants of cavemen. They thrive on high-intensity work outs, and are better off without eating too much dairy or grains. Those who are blood type A are the descendants of Ancient Farmers, and it is believed that the same intense workouts that pump up O's actually create more cortisol (the stress-hormone) for Type A's.
I believe it is a fairly even split between nature vs. nurture. A lot of our conscious behavior is based in the nurturing we received. Most of our unconscious behavior comes from nature (i.e. our flight or fight response in the amygdala).
There are hundreds and thousands of personality tests and quizzes. In just a few questions, they claim to be able to have a brief summary of exactly who you are. I love taking these things, even though most of it seems like surface level rubbish with little science behind the answer.
If your blood-type can dictate what's best for you eat and how you exercise, who's to say that it doesn't (even if it is just on a very small scale) effect the chemistry between two people?
Regardless of how it impacts our interactions with one another, I think it is important to be aware of how something as core and basic as blood-type can effect what you do.
Life is not one-size-fits-all; there will always be exceptions. True power and joy resides in understanding yourself.
How well do you know yourself? It's a journey, take (and enjoy) your time answering that question.