Human capital is your ability to earn an income. When you are young, your investable assets are small but your potential to earn income is in the millions for most people.
It should affect your portfolio allocations.
In a November, 2013 Journal of Financial Planning article by Bridges, De'Armond and Dean they wrote: "...With financial assets comprising a small portion of the total portfolio in relation to human capital, researchers have concluded that most households can afford to take on higher risk in the their financial portfolios...(Lee and Hanna 1995; Gutter 2000; Ibbotson et al. 2007)...."
I agree that your income is another important part of the calculation of your overall asset allocation and must be considered. It is subject to risks and therefore disability and life insurance may be possible solutions to minimize that risk. Not investing too much in your employer's stock, if available to you, is another.
Whether your income is "bond-like" (stable) or "stock-like" (commission only or more uncertain) is yet another element to include in this strategy.