Short answers, pulled from the story.
Humans are the species Homo sapiens, the most abundant and widespread of all primates. Homo sapiens emerged in Africa at least 300,000 years ago, descended from a species often called H. heidelbergensis or H. rhodesiensis.
Any two humans share between 99.5% and 99.9% of their DNA, which makes the species more homogeneous than chimpanzees. The greatest genetic difference, between 1% and 2%, exists between males and females rather than between geographic populations.
Humans left Africa in at least two waves, the first around 130,000 to 100,000 years ago and the second around 70,000 to 50,000 years ago. They reached Eurasia 125,000 years ago, Australia around 65,000 years ago, the Americas around 15,000 years ago, and remote islands between 300 and 1280 CE.
Human childbirth is dangerous because the fetus's head is matched more tightly to the pelvis than in other primates, which can cause labor lasting 24 hours or more. In developing regions, maternal death rates run roughly 100 times higher than in developed countries.
Humans have a larger and more developed prefrontal cortex than other primates and are the only animals known to cry emotional tears. They may be the only animals with episodic memory and the ability to engage in mental time travel.
More than 8.3 billion humans occupied almost all regions of Earth in 2026. Humans used roughly six thousand different languages, including sign languages, with many thousands more now extinct.
Between 167 million and 188 million people died as a result of war during the 20th century. The years since 1945 have seen a very significant drop in death rates from armed conflict, the steepest in 600 years.