The minimum wage of the man, it is true, need not cover the full support of his family, because the wife or children will on the average contribute something to their maintenance.

But the wage of the man must cover his own support, and part of the support of his family.

This marks a rigid minimum wage for male labour; if competition tends to drive wages lower, the supply of labour is limited to unmarried males.
The case of woman is different.

If she is a free woman her minimum wage will be what is required to support herself alone, and since a woman appears able to keep alive and in working condition on a lower scale of expenditure than man, the possible minimum wage for independent women- workers will be less than a single man would consent to work for, and considerably less than what a married man would require.

But there are other economic causes more important than this which drag down women's wages.
Single women, working to support themselves, are subject to the constant competition of other women who are not dependent for their full livelihood on the wages they get, and who, if necessary, are often willing to take wages which would not keep them alive if they had no other source of income.