significant variable within a non-significant model/block in hierarchical regression


I'm conducting a hierarchical (aka sequential) regression analysis with four blocks of variables. Block 1 consists of 5 covariates. Sex is one of these covariates, with the following breakdown: males (n = 213), females (15). Block 1 is not significant (R square = .04), though the variable, sex, is significant at p = .015. Sex continues to be significant in blocks 2 and 3 as well.

How do I make sense of the significance of sex within the non-significant block of covariates?

Is this a spurious result due to the lopsidedness of the sample?

Please let me know if you need more info. Many thanks.