Harvard history professor Niall Ferguson shares with Newsweek readers his concerns about obstacles to social mobility in America.

What has gone wrong? American liberals argue that widening inequality inevitably causes falling social mobility. This was what Alan Krueger, chairman of the Council of Economic Advisers, had in mind back in January, when he came up with the “Great Gatsby Curve,” showing that more unequal countries have less social mobility. (Hang on, wasn’t Gatsby a self-made bootlegger?) But to European eyes, this is also a familiar story of poverty traps created by well-intentioned welfare programs. Consider the case highlighted by Gary Alexander, Pennsylvania’s former secretary of public welfare. A single mom with two young kids is better off doing a part-time job for just $29,000 — on top of which she receives $28,327 in various benefits — than if she accepts a job that pays $69,000, on which she would pay $11,955 in taxes.

Another good example is the growth in the number of Americans claiming Social Security disability benefits. Back in the mid 1980s, little more than 1.5 percent of the population received such benefits; today it’s nearly 3.5 percent. Nor (as used to be the case) are the recipients mainly elderly. Around 6 percent of the population aged between 45 and 54 — my age group — are SSDI beneficiaries. Payments to disabled workers average $1,130 a month, which works out as $13,560 a year — just $2,000 less than a full-time wage at the federal minimum of $7.25 an hour.

In addition to detailing programs that discourage work, Ferguson describes how government efforts to “spread the wealth” also play a detrimental role.

According to the Urban Institute, the current share of federal spending on the young is around 10 percent, compared with the 41 percent that goes on the non-child portions of Social Security, Medicare, and Medicaid. Per capita government spending — including state and local budgets — is roughly double for the elderly what it is for children. Perhaps not surprisingly, the child poverty rate is more than double the poverty rate for seniors. Ask yourself: how can social mobility possibly increase in a society that cares twice as much for Grandma as for Junior?