Bill Gates reads 50 books a year and says this is his all-time favorite — here are his top highlights

and comes to the optimistic conclusion that we are living in the most peaceful era humans have ever enjoyed.

He analyzes 15 different indicators, like literacy, quality of life, and safety, and compares data to show how these have changed over time.

On his blog, Gates highlights what he thinks are the five most interesting facts from Pinker's book, and how they illustrate the ways in which the world is improving for the better.

Time spent doing laundry fell from 11.5 hours a week in 1920 to an hour and a half in 2014.

Technological innovations in the home have freed up people — especially women — to pursue "higher callings," like entering the workforce, pursuing advanced degrees, and creating art, Pinker writes.

The average amount of time Americans spent washing their clothes has fallen from 11.5 hours per week in 1920, to only around 1.5 in 2014, according to Pinker. He quotes Hans Rosling, a renowned physician and public health scholar, who says that the washing machine is the "greatest invention of the Industrial Revolution," for effectively giving people one day per week of their lives back.

But it's not just laundry where we're saving time. The average amount of time Americans spent on housework has fallen fourfold since 1900, from 58 hours per week — more time than a full-time job — to 15.5 hours in 2011, according to Pinker.

"But in most times and places housework is gendered, so the liberation of humankind from household labor is in practice the liberation of women from household labor," Pinker writes.

We have modern appliances, like refrigerators, microwaves, vacuum cleaners, and yes, washing machines, to thank for that.

You’re much less likely to die on the job than in the past.

Thanks to a push from engineers, lawmakers, unions, and journalists exposing how fraught the manufacturing-based workplaces of the early 20th century were, Americans are far less likely to die on the job than ever before.

In 1910, almost 70 American workers per 100,000 died on the job. That number has fallen to less than 5, according to Pinker's research.

This figure belies the recent nostalgia in political circles for a return to the US's manufacturing-based economy.

"With the shift from a manufacturing to a service economy, many social critics have expressed nostalgia for the era of factories, mines, and mills, probably because they never worked in one," Pinker writes.

According to Pinker, early reforms like employer's liability and worker's compensation were instrumental in incentivizing the creation of safer workplaces.

You’re 37 times less likely to be killed by a bolt of lightning than someone at the turn of the century.

The global average IQ score is rising by about 3 IQ points every decade.

Global IQ scores have increased by an average of three points per decade, the clearest sign we have yet that people are actually getting smarter, Pinker writes.

While intelligence is a highly heritable trait, improvements in nutrition, medicine, and cleaner environments have given our brains much more energy to develop over time. But that's not the only explanation for the rising trend.

Pinker writes that of all the subtypes of intelligence that the IQ tests for, it's the "abstract, fluid kinds of intelligence," that have shown the largest increases in the past decade.

These are defined as analytic thinking, like understanding and reasoning, and relating abstract objects to larger categories, and the increase is owed in part due to widespread, high-quality education.

"A high IQ is not just a number that you can brag about in a bar or that gets you into Mensa; it is a tailwind in life," Pinker writes, adding that people who score higher on intelligence tests end up getting into better schools, scoring better jobs, and earning more money over time.

War is illegal.

War between nation states — and the genocides and atrocities that came with it — is largely a thing of the past.

In the late 1940s, after the end of World War II, almost 25 people per year died violent deaths in battle. That number has fallen to less than 5, with a recent uptick due to the Syrian Civil War, according to Pinker.

And in terms of genocide, it appears we as a society really did learn a lesson from the Holocaust. The rate of death due to genocide has cratered since the 1940s, from well over 350 per 100,000 at its peak, to well under 5 today, according to Pinker.

The reason for this is because war, as conventionally defined, is largely illegal. Prior to the era of international bodies like the United Nations and complex, multi-party trade agreements, the old adage about warfare rang true:

"Might made right, war was the continuation of policy by other means, and to the victor went the spoils," writes Pinker.

Today, the world's nations have committed to not pursuing warfare for territorial gains or policy objectives, unless it is in self-defense or with the blessing of the UN's Security Council. While war still exists within states, and against non-state actors like terrorist groups — and the norm is sometimes breached — traditional warfare between states is largely a thing of the past.