Well, the short answer is no. We can't have more ancestors in a generation than the total known population of the earth at the time. Therefore it is estimated that 80 percent of marriages have been between first or second cousins and 100 percent of marriages will find a connection if you go back far enough. The cool thing about this reality is that you are very likely to find connections to rich, famous and historically significant figures if your ancestors came from the same general area as theirs during colonial times (New England for me). In fact, I am a 10th cousin of Barack Obama on his mother's side, the Dunhams.
If you're researching your family tree back to colonial times or earlier, you will find many, many others who are also searching for the same families and therefore your cousins. Besides the fact that it is statistically impossible to have 281 trillion European ancestors in your 30th generation, one needs to remember the lack of mobility people had prior to the 20th century. In previous centuries, most people were born, lived, and died in the same town. Then there are factors such as the inter-marrying of the European royal families. All of these factors lead to more cousins than distinct individuals in your family tree. I can't say it still doesn't freak me out a bit when I see it in my own family tree but understanding the mathematical, sociological and scientific realities helps. I found the following web sites interesting.
"Facts about Cousin Marriage " Cousin Marriage Resources. 24 Mar. 2012. Web. 24 Mar. 2012. <http://www.cousincouples.com/?page=facts>.
- We are all cousins - no two people are more distantly related than 50th cousins.
- Twenty-six states and all European countries allow first cousins to marry. It is also legal in Canada and Mexico.
- Leviticus 18 lists all forbidden sexual relationships. Cousin relationships are not included.
- Albert Einstein & Charles Darwin married their first cousins.
- Second cousins have little, if any increased chance of having children with birth defects, according to the book "Clinical Genetics Handbook." The National Society of Genetic Counselors estimated the increased risk for first cousins is between 1.7 to 2.8 percent, or about the same as any woman over 40 years of age.
R., Danielle. "10 Famous People Who Married Their Cousins." Listverse. Ultimate Listverse Top 10 Lists, 20 July 2008. Web. 24 Mar. 2012. <http://listverse.com/2008/07/20/10-famous-people-who-married-their-cousins/>.
- Jesse James & Zerelda "Zee" Mimms - 1st cousins
- Franklin Delano Roosevelt & Anna Eleanor Roosevelt - 5th cousins
- Johann Sebastian Bach & Maria Barbara Bach - 2nd cousins
- H.G. Wells & Isabel Mary Wells - 1st cousins
- Thomas Jefferson & Martha Wayles Skelton Jefferson - 3rd cousins
- Albert Einstein & Elsa - 2nd cousins
- Charles Darwin & Emma Wedgwood - 1st cousins
- Edgar Allan Poe & Virginia Clemm - 1st cousins; she was 7 when he moved into her home - her parents were his aunt and uncle & she was 13 when they married
- Jery Lee Lewis & Myra Gale Brown - she was 13 when they married
- Rudy Guiliani & Regina Peruggi - 2nd cousins
For more information, search "diamond theory of genealogy"