Pretty much anyone who was alive in 1620 will by now either have no descendants or a ridiculously large number of descendants.<p>If his descendants continued to breed at the rate of 2.5 children each at the age of 25 then by now he'd have approximately 1.6 million descendants in the latest generation (plus another million or so from their parents and grandparents' generations, still alive). Bump it up to an average of three children and we're looking at 30 million descendants. Bring the breeding age down to 22 and we're talking 287 million descendants, which just happens to be the population of the US. Of course you'd need to adjust that downwards since there'd be plenty of (mostly rather remote) inbreeding along the way.<p>If you could get a complete list of your (seven hundred thousand or so) ancestors dating back to the 17th century you'd probably be totally thrilled by the number of famous names on it. But of course, everyone else would have a similar number of famous names on their own.
Without analysis of the counter-factual, the list seems impressive. But had Howland died there is a high probability that there still would have been a 32nd, 41st, and 43rd US president; prominent 19th century poets; Alaskan governors; pediatricians and Hollywood leading men. And listing both Bush's seems gratuitous - why not list all the Baldwin brothers?<p>Probably the only two individuals on the list whose impact on US history might be considered irreproducible are Smith and to perhaps a lesser extent, Young because creating enduring spiritual systems [Mormonism] and political states [Utah] seems more dependent on individual characteristics than the roles filled by other individuals.
If you're a man and you have children, anything you did differently before you had them would have resulted in different children because your sperm would have shifted.<p><a href="http://econlog.econlib.org/archives/2008/06/parenthood_as_t.html" rel="nofollow">http://econlog.econlib.org/archives/2008/06/parenthood_as_t....</a>
If you're wondering whether the story is true or not, it appears to be. All of the relevant facts are present in John Howland's (heavily cited) Wikipedia article.<p><a href="http://en.wikipedia.org/wiki/John_Howland" rel="nofollow">http://en.wikipedia.org/wiki/John_Howland</a>