Challenging gender inequality is a choice. Since 1911, March 8 has been International Women’s Day. This year’s theme centres on challenging and calling out gender bias and inequality wherever it rears its ugly, sometimes unconscious, head. The occasion is a celebration of women’s achievements in the social, economic, cultural and political spheres. The day is being promoted worldwide with the social media hashtag #ChooseToChallenge. Beyond the balloons, hashtags and rubber wristbands, this is a global call for gender parity. International Women’s Day, first and foremost, is about the eradication of gender inequality, and ensuring equal access to resources and opportunities, regardless of gender. The first step is an awareness that problematic gender differences exist. The social sciences, and psychology, in particular, have a long history of uncovering such differences. It is almost a cliche that undergraduate psychology students do research comparing some attribute or another across genders – for example, men versus women on self-esteem. I don’t think this is always particularly useful or interesting. It is just easy to do. Comparing men and women is often the low-hanging fruit of research; gender is simply a very convenient grouping variable. Knowing that there is a gender difference is not nearly as useful as knowing why the discrepancy exists. For example, in many nations, women are diagnosed with clinical depression at much higher rates than men. In the community psychiatric survey in Al Ain, for instance, depressed women outnumbered depressed men almost 4 to 1. The authors of this study, published in <em>Social Psychiatry and Psychiatric Epidemiology</em> in 2001, suggested that gender difference was related to the reluctance of men to report depressive symptoms. But why would men be less likely to report the symptoms of depression? Here, we get to the heart of the matter. Before her death in 2013, Susan Nolen-Hoeksema, a professor of psychology, headed the Yale Depression and Cognition Programme in the US. For Nolen-Hoeksema, gender differences in depression started in childhood. She argued that young boys are typically discouraged from “sissy” displays of emotion, whereas young girls are indulged. Girls and boys are also bombarded with ill-founded tropes, such as the idea that “women are naturally emotional”. For Nolen-Hoeksema, such experiences and ideas result in women being more likely to overthink in response to sadness. Excessive rumination is a well-established gateway to depression. The fact that we treat infants differently based on their assumed sex is also well-established. In a now-classic study, researchers randomly dressed male and female babies in blue or pink. Whether the baby was thought to be a boy (wearing blue) or a girl (wearing pink), adults played with the infants using gender-stereotyped toys, for instance, with hammers or dolls. In another study, adults watched a video of an infant’s reaction to a jack-in-the-box. When adults believed they were watching a girl, they interpreted the child’s response as fear. If they thought the infant was a boy, then the same reaction was seen as anger. Such early life experiences shape the way we generally respond to emotions. Men, for instance, are far more likely to try and “shake it off” when sadness descends. This tendency perhaps explains the higher rates of illicit drug and alcohol dependence worldwide among men compared to women. Similarly, let's suppose we slightly alter the criteria for depression and look at anger and hostility, rather than sadness and worthlessness. In that case, the gender differences for depression start to evaporate. A growing number of mental health professionals argue for a new form of depression to be added to the diagnostic system – one characterised by anger. It is argued that making this distinction will help clinicians identify depression in men. There are many other examples in which apparent gender differences can be traced back to social, cultural and historical influences. For instance, in many nations, the UAE included, we observe gender differences in levels of university attendance (more women) and performance (better results). According to the US Department of Education, 56 per cent of university admissions are now women, projected to rise to 57 per cent by 2026. Women in higher education generally outperform men, too, and males are far more likely to drop out. Several ideas are advanced to explain the underrepresentation and underperformance of men at college, from gender differences in early language development to economic woes. However, perhaps part of the explanation is also tied to the historical lack of access to education for women. If access to something was once restricted, then we value it all the more when we get it. It is easy to see how valuing higher education would translate into superior performance and lower dropout rates. Research has done much to explore gender differences. However, across some of the significant psychological domains – personality, cognitive ability and leadership – men and women are more similar than they are different. Psychologist Janet Shibley Hyde of the University of Wisconsin-Madison pooled 46 major studies exploring gender differences across various psychological domains. Published in <em>American Psychologist</em> in 2005, the take-home message was clear: from childhood to adulthood, men and women are more alike than different on most psychological variables. Ms Hyde dubbed her finding the "gender similarities hypothesis". While we do occasionally observe gender differences, these are frequently the consequence of historical and social influence. In some cases, such differences are perpetuated by gender bias and systemic, institutionalised gender inequality. These are things we should all choose to challenge. When our societies value individuals equally – when we choose to challenge – they are safer, healthier, happier and more prosperous. <em>Justin Thomas is a professor of psychology at Zayed University and a columnist for The National</em>