Here Comes Grand Dad Again: Exercises for Skeptics:
1) Look in the mirror. Note similarities in your eyes, nose, forehead, chin, mouth, and neck to the same structures in other family members. Do the same for mannerisms, even the way you eat your eggs. Look for similarities in sports interests (of lack thereof), hobbies, and vocations. Record your chief weaknesses and your vices. Again, look for similarities.
2) Sit in the Mall on a Holiday. (Halloween works pretty well because both parents and all their kids are present in groups, traveling store to store, picking up treats from the merchants.) Take a look! Watch their gaits, the tilt of their heads, the way they chew gum.
3) Get out old photographs and movies of your parents when they were your age. Go through family albums and look for bits of yourself. Try to spot the features that tell you whether someone is related to you.
4) Count the number of things you say, especially to your children, that irritated you when you heard them from your own parents. Especially the lines that you swore that you would never repeat.
5) Note whether your spouse is acting and looking more like her parents despite promising never to do so. If environment were the key variable, you both should become less, not more, like your parents as you get older.
6) Inventory your children's learning strengths and difficulties. Compare them with your own and with your mate's difficulties and assets. (I know one adolescent who falls to sleep whenever he reads for 10 minutes; he also has difficulty copying the teacher's notes and listening to the lecture at the same time. His father had and still has similar difficulties.)
7) You may have a child who looks and acts like no one else. Before you ask for DNA scans, check the uncles and aunts on both sides of the family; you will possibly find another, older version of you child. If not, then do the DNA. (Just kidding!)
8) You may also have a child with emotional difficulties. Check your own history as well as that of your spouse and both sets of grandparents. Look for similarity of mood as well as similarity of onset dates and social situations. Survey things that seemed to help the earlier generation overcome their difficulty; you may get some useful ideas for your own child.