Initial conditions important for successful life outcome

Haven't gone through the actual paper. The title link is to Marginal Revolution for expanded excerpt, comments and another link to a story on early mental health problems affecting adult life. Don't know how they're referring to "human capital" here:

We find that as of age 20, differences in initial conditions account for more of the variation in lifetime utility, lifetime earnings and lifetime wealth than do differences in shocks received over the lifetime. Among initial conditions, variation in initial human capital is substantially more important than variation in learning ability or initial wealth for determining how an agent fares in life.