(CNN) - An author of a highly critical report on pending immigration legislation has resigned his post at the conservative Heritage Foundation after his previous writings, including a dissertation citing lower IQ among immigrants, drew widespread anger.
"Jason Richwine let us know he's decided to resign from his position," a spokesman for the Heritage Foundation said Friday. "He's no longer employed by Heritage. It is our long-standing policy not to discuss internal personnel matters."
Richwine, who was described on Heritage's website as a quantitative analyst, penned a 2009 dissertation at Harvard titled "IQ and Immigration Policy" that asserted in its summary the "average IQ of immigrants in the United States is substantially lower than that of the white native population, and the difference is likely to persist over several generations."
His paper argued for a policy that sought out immigrants with higher IQs, which he claimed would ameliorate problems currently affecting immigrant populations like "a lack of socioeconomic assimilation among low-IQ immigrant groups, more underclass behavior, less social trust, and an increase in the proportion of unskilled workers in the American labor market."
The linking of immigrants with lower IQs drew outcry, and was met with a swift response from the Heritage Foundation, which said Richwine had no role in devising the methodology of the group's own immigration report, released this week.
"The Harvard paper is not a work product of The Heritage Foundation," wrote Mike Gonzalez, vice president for communications at Heritage, on Wednesday. "Its findings do not reflect the positions of The Heritage Foundation or the conclusions of our study on the cost of amnesty to U.S. taxpayers, as race and ethnicity are not part of Heritage immigration policy recommendations."
Richwine's dissertation was crafted while he "was a student at Harvard, supervised and approved by a committee of respected scholars," Gonzalez wrote.
The Heritage report released Monday, called "The Fiscal Cost of Unlawful Immigrants and Amnesty to the U.S. Taxpayer," has two authors listed: Richwine and Robert Rector, a senior research fellow in domestic policy at Heritage.
The report determined that creating a legal pathway for the 11 million undocumented immigrants currently in the country would cost taxpayers a minimum $6.3 trillion over the lifetime of those immigrants. It also argues the average undocumented immigrant is 34-years-old, has a 10th grade education, and receives $14,387 per household in government benefits in excess of taxes paid.
Those conclusions were questioned by advocates for the new immigration reform bill, including Republican Sen. Marco Rubio, a key author of the Senate "Gang of Eight" measure.
"I don't believe their report is really legitimate. I have a lot of respect for Heritage, but I don't believe their report is a legitimate one," the Florida Republican told CNN en Español's Juan Carlos Lopez, arguing that improving America's system of immigration would actually help bolster the economy.
"If they are legalized, they will be able to work and pay taxes, they'll be able to open businesses and in due time improve their financial situation and contribute to the country's wellbeing and not hurt the country," Rubio said. "So that's why I strongly disagree with that report."