With the news that US Rep. Steve Lynch has joined Attorney General Martha Coakley in taking out nomination papers for US Senate, the first two candidates in the Democratic primary race may be the ones most hoping that lots of others join the fray.

That’s because a basic tenet of multi-candidate contests, which can fairly be described as the Sesame Street Principle, is that advantage accrues to the candidate who is the most distinct from the field. On Sesame Street, the thing not like the others gets shunted off as the one that “doesn’t belong.” In a crowded primary field, the one most unlike the others could emerge as the winner.

For Lynch, the South Boston congressman who is probably the most conservative member of the state’s all-Democratic DC delegation, the bigger the field of candidates who all lean to his left the better. For Coakley, barring the entry of Vicki Kennedy, each new candidate from the pool of potential Democratic contenders would be one more man in the race adding another exclamation mark to her status as the lone woman in the field.