Updated

A co-author of a disputed Heritage Foundation report on a new immigration bill has resigned amid controversy over claims he made about immigrants having low IQs.

A spokesman for the conservative think tank confirms Jason Richwine's resignation without offering any details.

Richwine was one of two authors of a report released Monday that said immigration legislation pending in the Senate would cost $6.3 trillion over 50 years as immigrants consumed federal benefits without making up for it in taxes. The report quickly came under attack as critics from the left and right said it didn't account for economic benefits from immigration.

Attention focused on Richwine when his 2009 Ph.D. dissertation from Harvard University surfaced in which he asserted that immigrants have lower IQs than the "white native population."