A timeline of human experience

Humanity has been around for a long time. About 300,000 years. For almost all of that time, people lived as hunter-gatherers or in tiny agricultural lived in settled, state-based societies as we do now.

But the world’s population was also very low for much of that time. Because there are about 8 billion of us today but fewer than one million people 100,000 years ago, each year of the modern era contains far more total “people-years” of lived experience.

A single calendar year in 2025 “contains” more human life than a year in 100,000 BCE, simply because today’s population is thousands of times larger.

One way to visualise history is to ask: at every point in time, how many total people-years had accumulated so far? (1)

The graphic divides history into ten equal “blocks” of experience: each block represents 170 billion people-years.

With an average population of roughly 600,000, it took nearly 300,000 years of prehistory to rack up the same 170 billion people-years that humanity has now accumulated in just the last 25 years.

By this estimate, 1300 is the half-way point of humanity. Half of human experience took place before 1300, and half took place afterwards.

This also lets answer some questions that may or may not be of interest:

• What percent of human experience has been lived in the past 25 years? A whopping 10%

• What percent of human experience has taken place since the Industrial Revolution? A little over 1/3.

• What percent of human experience took place before the first human settlements (~6000 BCE)? Approximately 10%.

• What percent of human experience has taken place since the birth of Jesus? Around 75% (2).

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1. People-years are calculated by taking the world’s population, and multiplying by the number of years that population lived. So in a world with population 8 billion, every year that passes makes up 8 billion people years. In a world with a constant population of 100 million, it would take 80 years to create 8 billion people-years (100 million × 80 = 8 billion).

For you nerds out there, this is the integral under the population curve.

2. A couple other articles of interest:

• David Bieber writes on the percent of human experience from lived people

• The good people at PRB estimate how many people have ever lived

• As do the good people of University of Hawaiʻi at Mānoa

Due to different methodologies and assumptions, some of them have answers that differ from mine by up to a factor of 2. For example, my analysis implies that about 1.7 trillion people-years have been lived, as opposed to 3.2 trillion from David Beiber. But what’s a factor of 2 among friends?

Half of the kids used to die

Half of the kids used to die.

Across societies with very different climates, cultures, and forms of governance, half of children died before the age of 15. People tried to stop children from dying, and they just failed.

Our World in Data

Things are much much better now. Worldwide childhood mortality is now 4%. In Niger it’s the worst, and it’s still only 15%.

15% of children dying is awful, but it’s way less awful than 48%. Prior to 1800, any country that achieved a child mortality rate of 15% would be seen as the absolute pinnacle of good governance and public health.

Half of children used to die, and now they don’t. If you were making a list today of the top 10 most important facts about the world, this would definitely be in it.

Previous generations have worked hard, and given us the gift of a world where only one in twenty-five children die.

It’s still too many! It’s up to us to give future generations a world where less than 0.5% of children die. It’s possible! It’s already the case in Finland, Norway, Japan, and Slovenia.

If you find yourself thinking that modern life is terrible, just remember that half of children used to die.

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This post is essentially just my reflections on this much better post from Our World in Data.

Why the US dropped atom bombs on Japan (more Oppenheimer context)

Since watching Oppenheimer I’ve been thinking a lot about the factors that went into the US dropping two atomic bombs on Japan.

The official reason given by President Truman and Secretary of War Stimson is that doing so saved hundreds of thousands - maybe millions - of US lives that would have been spent in making a land invasion of Japan.

In reality there there was no single decision made to drop the bomb based on the lives that would be saved (1). It’s simply that all the momentum of the wartime USA was pushing towards dropping the bomb.

Think of the various political factors going on:

• The US had been calling for the unconditional surrender of Japan, and Truman felt the US public would not accept anything less - to an extent Americans felt angry and vengeful towards the Japanese. The bomb seemed that it would help convince Japan to unconditionally surrender

• The US was eyeing post-war diplomacy and wanted to impress and shock the USSR with the weapon

• The bomb had cost $2 billion to build. When an inevitable congressional inquiry into the project occured, everyone involved wanted to be able to show without a doubt that the money was well spent

• As General Leslie Groves, head of the Manhattan project, said: “Knowing American politics…there would have been elections fought on the basis that every mother whose son was killed after [the date we could have dropped the bomb] the blood is on the head of the president”

Imagine you are a top decision-maker tasked with making decisions trying to win the worst war that has ever been fought. You are simply going to use every weapon you have. You would have to be a person of incredible moral conviction to say “we should not use this weapon because of the moral repercussions”.

Nobody in a decision-making position stood up like this - not Truman, not Secretary of War Stimson, not General Marshall.

The reason the US built and dropped and continued building bombs is because everything in the manner in which World War II was prosecuted, American sentiment towards Japan, and the way policymakers viewed the USSR, pushed towards dropping them.

For a lot of people who worked on the bomb, the original intention was to make sure the US built it before the Nazis did. But once the gears of government power-accumulation are kicked into motion, original intentions stop mattering. A chain reaction is started and is very difficult - maybe impossible - to stop (2).

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I do not consider myself a leftist or someone who generally thinks that we need to tear down and rebuild the entire structure of American society and government. But I wonder: Maybe it is worth tearing it all down if that’s the price we have to pay for a system of government where political pressure doesn’t lead to dropping atomic bombs.

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1. In fact, Truman simply lied in his “estimate” of the number of lives that would have been lost. The actual estimate of lives lost given by the Joint War Planning Committee was 40,000.

2. Ina similar vein, a major factor in the US building up its nuclear arsenal during the cold war was competition between different branches of the military for more influence and a larger share of the budget. Here is Richard Rhodes: "what the Air Force figured out by the late 1940s is that the more targets, the more bombs. The more bombs, the more planes. The more planes, the biggest share of the budget. So by the mid 1950s, the Air Force commanded 47% of the federal defense budget. So the Army discovered that it needed nuclear weapons, tactical weapons for field use, fired out of cannons. …And of course the Navy by then had been working hard with General Rickover on building a nuclear submarine that could carry ballistic missiles underwater in total security…We would be perfectly safe if we only had our nuclear submarines. And only one or two of those. One nuclear submarine can take out all of Europe or all of the Soviet Union.”

Some Oppenheimer context on science and the military (no spoilers)

I’ve been learning a lot recently about the Manhattan project – such a fascinating and dramatic time. I thought some of this might be interesting to other people who recently saw or are thinking of seeing the movie Oppenheimer (1).

Most of what is below comes from the book A World Destroyed: Hiroshima and its Legacies (2).

• The reason the bomb was developed under the Army and not the Navy was because Vannevar Bush – one of the top science advisors in Washington DC (3) found that the Navy officers he worked with tended to not want advice from scientists and to do things their own way, while the Army (especially Secretary of War Simson) were much more collaborative

• Oppenheimer had to work hard to convince Bush that a lot of top scientists should be moved away from the Rad Lab at MIT (where they were developing RADAR technology that was obviously crucial to the war effort) and to the Manhattan project (where it wasn’t clear if a bomb would be built in time to be used during the war)

• He then had to work hard again to convince those scientists to move to the middle of the desert where they were worried they would be under military control

• In general, scientists working on the Manhattan project were very worried that they would have to be subject to military discipline. Eventually Oppenheimer was able to convince Leslie Groves that they would not get the best scientists unless Los Alamos remained under civilian control, which it did throughout the war

• Scientists working on the Manhattan project felt that they were taking the project much more urgently than the military. They often felt that the army – with all its attempts to compartmentalize information by restricting communication between scientists – was slowing down their ability to build the bomb and potentially letting Hitler build the bomb first

• Some people credit the scientist’s – including Oppenheimer’s – insistence on not following compartmentalization as one of the key factors in moving quickly enough to construct the bomb in time to use it against Japan

• This sentiment was especially prominent in Chicago. After Fermi’s team in Chicago demonstrated the first nuclear chain reaction in December 1942, basic research was almost completely removed from Chicago and to the rest of the Manhattan project sites. Chicago scientists felt left behind, and became increasingly vocal against how the army was handling the administration of the project.

• Towards the end of the war, the Chicago scientists tried to convince Washington not to drop the bomb on Japan. They had a strong sense that – since they had helped develop the bomb – they should have a strong voice in how the bomb be used

• In retrospect this sentiment – expressed by other scientists before and after the war – seems pretty naïve. Contributing to building a weapon doesn’t mean you get to determine how it’s used. But before World War II, theoretical physicists were seen as pretty useless. There certainly wasn’t a lot of collaboration between theoretical physics and the military. Many of these scientists didn’t know at all how the military world worked.

• From the perspective of the military, and from both Presidents Roosevelt and Truman, there wasn’t much of a question of if the bomb should be used or not. From a political-military perspective, during an all-out war, you do not invest billions of dollars and the effort of top scientists to build a weapon and then not use that weapon

Also valuable to know that Edward Teller (the awkward arrogant Hungarian in the movie) was a very strong nuclear hawk and would go on to be “the father of the hydrogen bomb”.

Hopefully that helps you appreciate some the of the background of what is going on in the movie! I’m excited to watch the movie again knowing all this now (4) (5).

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1.       For the interested, here is a post I wrote that touched on my views of the morality of the Manhattan Project, as well as another post with my thoughts on Christopher Nolan’s movies (and physics!)

2.       The author is Martin J Sherwin who is also one of the authors of American Prometheus – the biography of Oppenheimer that the movie is based on

3.       And famous MIT professor and administrator – shout out. He is the tall spindly kindly-looking bespectacled high-up in the movie

4.       If I’m wrong about anything in this post, please let me know! I’m trying to form a more accurate view of everything that was going on in science and politics at this time and would love to be corrected

5. I also love what Leslie Groves (Matt Damon’s character) says about the decision not to travel by air:

Mr. Stimson [Secretary of War] told me that if I went, I could not go by air, because of the hazards involved. When I said, “Well I don’t see what difference that would make,” he replied, “You can’t be replaced.” I said, “You do it, and General Marshall does it; why shouldn’t I?” He repeated, “As I said before, you can’t be replaced and we can.” Harvey Bundy, who was also present, said he had heard that I had previously urged flying when air safety dictated otherwise and then asked, “Who would take your place if you were killed?” I replied, “That would be your problem, not mine, but I agree you might have a problem.”

From Now It Can Be Told: The Story of the Manhattan Project.

How did China's life expectancy increase?

I was all ready to write a very different blog post than this one.

I recently learned that in the early 50s, the people of China and India had similar health outcomes, but now China is much much healthier. For example, China’s life expectancy is 78, compared to 70 in India. On the basis of this, I was ready to write a post saying “do you see how important economic development is? It’s not just about having nicer clothes and cares - it’s about saving lives!”

But it turns out that the evidence from the China-India case actually goes largely against that narrative. Because China’s biggest improvements in health outcomes came between 1950-1979 - before its economic growth, not as a result of it.

As Jean Drèze and Amartya Sen say in book I’m getting most of this information from:

“The Chinese level of average opulence judged in terms of GNP per head, or total consumption per capita, or food consumption per person, did not radically increase during the period in which China managed to take a gigantic step forward in matters of life and death, moving from a life expectancy at birth in the low 40s (like the poorest countries today) to one in the high 60s (getting within hitting distance of Europe and North America).”

So what did China do to make its people so much more healthy compared to India? To the best of my understanding from an hour of Googling, it was largely a result of:

• Mass public health initiatives such as midwife training, campaigns against malnutrition, and immunization promotion. Interestingly, “patriotic overtones and mass citizen involvement of these campaigns contributed to their success”

• Improved education: Apparently experts don’t know exactly how a population being better educated leads to being healthier, but it is accepted as a general trend. In 1949, Chinese primary school enrolment was 20%. It was up to 80% in 1958 and then 97% in 1975.

• Relatively egalitarian distribution of food: This was possible because rural people had land and urban people had jobs. The work communes also seemed to help ensure the poorest people had access to food (1).

This is a corrective my general assumption that to drive the most important outcomes for a poor society (health, security, happiness), it’s best to just focus on economic growth. Turns out those commies did a great job improving health by focusing on health, education, and food.

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1. This access to food in China has the notable exception of the famine of 1958-61 where 17-30 Million people died. But for perspective, Drèze and Sen claim that that many people die in India every 8 or so years from malnutrition.

Democracy in India may have protected it from famine, but it does not protect it from chronic malnutrition:

“as India's experience shows, open journalism and adversarial politics provide much less protection against endemic undernutrition than they do against a dramatic famine. Starvation deaths and extreme deprivation are newsworthy in a way the quite persistence of regular hunger and non‐extreme deprivation are not.”

"We just need a good leader"

I was in Pakistan for a wedding a few weeks ago (1) and was talking to someone about Pakistan’s history. I asked “Wo do you think is the best leader Pakistan has had?”

He answered that other than their founding father, Jinnah, he didn’t think Pakistan had had any good leaders and that this was one of the main reasons Pakistan had troubles.

This reminded me of something I’ve heard people say in Kenya: “the problem with Kenya is that our politicians are greedy.”  I’ve heard Americans say a similar thing.

If a country 1 out of 5 leaders who does a really bad job, then maybe that person is just a bad leader. But if a country has 5 bad leaders in a row, then you have a systemic issue, not a personality issue.

So why do we focus so much on the individual leader, and try to pin our hopes and assign blame to them?

It’s not a big mystery: It’s much easier to think at the level of individual narrative and blame rather than think about the drivers of a system of societal governance.

I don’t think it’s bad to think about the virtues and defects of individual leaders – those traits do matter, they are interesting to explore, and that exploration can teach us about a person’s ability to maneuver within a political system. But it’s helpful to keep in mind that we overestimate the importance of individual traits, and underestimate the importance of the overall system.

Why else would I have asked him who he thought Pakistan’s best leader was without asking anything about the political system overall?

So next time I ask someone about their favorite political leader, I will follow up with asking “and what about the political environment they operated in allowed them to do good where others did bad?”

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1.       The Pakistan trip was awesome and I’ll have another post soon with more about what I saw and learned

The Past is Just a Foreign Country

 “There are young people today who feel that we shouldn’t have developed the atomic bomb, that it was a mistake. And I believe that this is because – through no fault of their own – they don’t have this sense of history. They didn’t live through this almost terrifying period when we thought we were losing the race with Adolph Hitler.” Chemist Glenn T. Seaborg, who worked on the Manhattan Project

“The past is a foreign country; they do things differently there.” ― L.P. Hartley, The Go-Between

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How should we feel about people in the past who did bad things? It’s a question all of us who have too much time on our hands like to overthink about.

I think I’ve solved it: Just think of the past as a foreign country.

You don’t judge people in a foreign country the same way you judge your own. You understand they have a different culture.

I live in Kenya. The moral lens I apply to issues here is different than the lens I apply in the US.

• I just don’t have opinions some issues: Some men (mostly from the countryside) practice polygamy (1). If I met someone espousing polygamy in the US I would say “don’t do that.” But in Kenya, since I come from such a different culture, it just feels like I don’t need to have an opinion on the matter.

• Some issues I am fine to express judgement on: A minority of people illegally practice female genital mutilation (2). It is seen as tradition in the culture of some tribes. I think this is very bad and the fact that I am not from those tribes does not stop me from saying so.

I’ve been thinking about this while learning about people working on the Manhattan Project (3). It’s been helpful to be able to say to myself “I have not lived with a fear of Hitler. The context I live in now is very different from what they lived in. So I don’t always need to morally judge their actions.”

I am confident it was morally wrong to drop atom bombs on Japan. I am not sure if it was morally wrong to develop the bomb in the first place.

Learning lessons from history is different from morally judging people’s actions in the past. We should try to learn as much as we can from the mistakes and successes of people who lived before us. But in judging them, try thinking of them like people living in a foreign country.

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1.      Allegedly 10% of married people

2.      Prevalence of 21% as of 2014)

3.      Questions around the early development of nuclear weapons feel very relevant to today’s issues around AI – should the US develop AI quickly to stay ahead of China and Russia?

Also I’m an Oppenheimer prepper.

Anti-eugenics research in 1930s Iowa

I came across the book The Orphans of Davenport: Eugenics, the Great Depression, and the War Over Children's this week, and thought it would be interesting especially to the Iowans who read my blog. It tells the history of psychological research in Iowa in the 1930s that unsuccessfully (at the time) tried to to overturn beliefs about eugenics.

In the 1930s psychologists thought that IQ was fixed by genetics, that environment didn't matter that much, and that maybe people with low IQs should be sterilized. Biologists had largely dropped these views, but they persisted in psychology.

Then some researchers at University of Iowa realized:

• hmm, when we put kids from intelligent parents in orphanages where they are neglected, they get less intelligent

• hey, when kids who don't seem smart are taken from neglectful orphanages and put with loving families, they get smarter

• wow, the longer a kid is exposed to neglect, the less intelligent they seem to be

Turns out that the environment a kid is raised in has a much larger effect on their intelligence than their genetics.

These were wild and surprising findings at the time and caused an uproar in the US psychology community. They were essentially buried, the researchers reputations' tarnished, and everyone went back to thinking that genetics were all that mattered. Then the Nazis made that super unfashionable, and psychology finally moved away from eugenics post WW2.

A very interesting book if you're interesting in the history of psychology, Iowa, or attitudes towards intelligence/eugenics. I skim-read the book in ~2 hours. It's nice that someone cataloged all this detail about the personalities involved, but it wasn't what I was interested in.

This book is probably more pro-Iowa than any other book I have read is pro any state. I'm from Davenport and have a brother with Down Syndrome, so there's definitely wishful thinking on my part to believe that historically Iowa has been at the front of anti-eugenics and nurturing children who would otherwise be left behind. But from what I can tell based on what is presented in this book, there is some truth to this view.

Other interesting bits to me:

• Basically none of rural Iowa had no electricity in the 30s (tracks with what my grandma has told me)

• Babies in the Davenport Home (now Annie Wittenmeyer for any Davenportians) were just put in cribs and left to sit there for months. They were fed and changed, but the only stimulation they had was the sunlight on the ceiling: "Light to shadows to darkness and then light again would have been everything she learned about the world."

• The culture of the Iowa Station (research station at University of Iowa) was critical to allowing the truth-seeking - rather an accepting given psychological dogma. Great management and institutions really matter!