The 102 passengers who set sail on the original Mayflower on Sept. 6, 1620, did not have such an auspicious send-off.

There were no Coast Guard boats to protect them, no hand-held G.P.S. instruments to determine their exact location, and worse, they were leaving two months late, heading into the uncertainty of a New England winter, much colder than anything they had known at home.

By April 1621, three months after the Mayflower's passengers settled at Plymouth, half had died of the cold and disease.

But eight American presidents can trace their ancestry to the 55 survivors, who over time came to be known as the Pilgrims. And, perhaps in defiance of the laws of mathematics, 25 percent of the American people today believe they are descended from the Pilgrims, according to a survey done last November for the General Society of Mayflower Descendants.