 At conception, a sperm carrying either an X or Y chromosome fuses with an egg which carries an X chromosome. In this process, a single cell called a zygote is formed. The combination of chromosomes inside the cell decides if the baby will be a boy or a girl. An X and a Y chromosome create a male, and two X a female. Around 1 in 5,000 of us happen to get a different chromosome combination. They are sometimes referred to as intersex, and a proof that something as binary as male and female can be on a spectrum. For simplicity, we will compare typical men and women. At birth, children are typically identified as boys or girls. Boys tend to be slightly larger and heavier than girls. Their heads are often a bit bigger too. Within weeks, cultural norms start to reinforce traditional gender roles. This makes it difficult for scientists to know what behavioral differences are biological and which ones are socially constructed. During childhood, boys tend to be more physically active, exhibiting greater interest in objects and exploration. They also begin to have a better understanding of three-dimensional space. Girls are less active, take a higher interest in people, and seem to form a better understanding of them. They also learn new languages faster. At just 16 months, girls, on average, have a vocabulary of 95 words, more than three times that of boys. In puberty, kids become teenagers. Their bodies change, and the differences between boys and girls become more obvious. Around the ages of 8 to 13, girls start to get taller, their body shape begins to change, and hair grows in new places. This continues into their mid to late teens. Puberty also brings the start of their menstrual periods. Technically, they can now become pregnant, give birth, and feed their baby. They also have elevated levels of the hormone estrogen, a highly social, and tend to show more empathy. Physically not as strong as their male counterparts, they exhibit a greater capacity to endure pain and can rival men in ultra-endurance runs. Boys enter puberty a bit later, with a growth spurt that peaks around age 14. They develop more muscle mass, body hair, and a larger Adam's apple, which gives them a deeper voice that can intimidate some and attract others. Boys also produce more testosterone and develop a higher regression potential. They are now larger, faster, significantly stronger, and about 10 times more likely to end up in jail. Some teens now identify as a gender different from the sex assigned to them at birth, and about 3 to 10% enter their reproductive years with an interest in the same sex. During their reproductive years, and until their mid-30s, both sexes are typically very good at making babies, but they face two very different risks. Women can technically make a baby in minutes. Women however, have to invest many months into pregnancy and give birth, with vast physical and psychological consequences. This puts them at a lot of risk if the relationship breaks apart, however they do have one advantage. Once the newborn arrives, mothers can be certain that the infant is theirs. A father that loves and cares for a child risks finding out it is not his, and depending on the culture, 1 to 10% do unknowingly raise another man's child, so what's mum's baby is papa's baby. A woman's anxiety about becoming a mother with no help supporting the family and a man's fear of paternal fraud is said to create some very different concerns about cheating. One theory hence suggests that men tend to worry more about sexual infidelity. They want to make sure they're raising the child they fathered. Women typically get more jealous when they feel emotionally betrayed. They worry that precious family resources are shared with someone else. In mid-adulthood, men and women begin to lose some of their ability to make babies. If we study fertility by age, we see that women's fertility drops from their early 30s, and by their 40s, chances of getting pregnant naturally are slim. Around their 50s, they enter menopause, and their periods stop. Men remain reproductive much longer, but from age 35, the chance of producing a faulty sperm cell increases exponentially with each passing year. As they reach late adulthood, women live longer. Men die about six years younger, often because of heart failure, perhaps because they don't care as much about their health and live a more risky life. What do you think? How does sex differences influence our society, and how does society influence them? And should we create laws and regulations to purposefully reduce the differences? Share your thoughts and comments below. If you like this video and want us to make more, subscribe to our channel or support us on Patreon.