A new McKinsey study released this week found that inadequate career development has held women back from leadership positions. If women make up more than 50 percent of the U.S. population, why don’t they hold 50 percent of the country's positions of power? In The Wall Street Journal, Diana L. Taylor, managing director of the investment and advisory firm Wolfensohn & Co., outlines several factors that are preventing American women from rising to the top. First, to compete and succeed in global business often requires travel and business trips which are harder for women with families than they are for men, since women are still widely regarded as primary caregivers. This suggests that human nature is at the root of the gender gap, particularly when it comes to leadership roles within highly competitive corporations. Some food for thought: Last year, McKinsey published a study that found companies with more women in positions of power do better than those where women are not leading the ranks.