No demographic data exist for more than 99% of the span of human existence. Still, with some assumptions about population size throughout human history, we can get a rough idea of this number: About 117 billion members of our species have ever been born on Earth.
By 10,000 B.C., the world's population was around 1 million. 2,000 years later there were about 5 million people on Earth—the same number that live in Finland today. 200 million people were scattered around the earth by 1 A.D. 1 in every 200 lived in Rome.
For the time of speciation of Homo sapiens, some 200,000 years ago, an effective population size of the order of 10,000 to 30,000 individuals has been estimated, with an actual "census population" of early Homo sapiens of roughly 100,000 to 300,000 individuals.
As recently as 12,000 years ago, there were only 4 million people worldwide. The chart shows the rapid increase in the global population since 1700. The one-billion mark wasn't broken until the early 1800s.
Earth's capacity
Many scientists think Earth has a maximum carrying capacity of 9 billion to 10 billion people. [ How Do You Count 7 Billion People?]
Overcrowding leads to further demand for limited resources and this, in turn, can lead to more conflict and warfare. As humans seek out more resources, they take over land that was once the habitat of other species leading to huge biodiversity loss.
The current world population of 7.6 billion is expected to reach 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion in 2100, according to a new United Nations report being launched today.
The fossil record indicates that Homo sapiens has been around for 315,000 years or so, but for most of that time, the species was rare—so rare, in fact, that it came close to extinction, perhaps more than once.
New genetic findings suggest that early humans living about one million years ago were extremely close to extinction.
Broadly speaking, evolution simply means the gradual change in the genetics of a population over time. From that standpoint, human beings are constantly evolving and will continue to do so long as we continue to successfully reproduce.
The only realistic scenario for the evolution of two species out of ours would probably be if we expanded beyond our home planet and then lost contact with the settlers. If both populations survived long enough – much more than 100,000 years – we might see divergence and maybe two species of humans.
Research carried out for this study indicates that the first speech sounds were uttered about 70,000 years ago, and not hundreds of thousands or millions of years ago, as is sometimes claimed in the literature.
With this context and timeframe in mind, the demographers estimate that 109 billion people have lived and died over the course of 192,000 years. If we add the number of people alive today, we get 117 billion humans that have ever lived.
The UN estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960.
Researchers have announced the naming of a newly discovered species of human ancestor, Homo bodoensis. The species lived in Africa about 500,000 years ago, during the Middle Pleistocene age, and was the direct ancestor of modern humans, according to scientists.
It took 13.8 billion years of cosmic history for the first human beings to arise, and we did so relatively recently: just 300,000 years ago. 99.998% of the time that passed since the Big Bang had no human beings at all; our entire species has only existed for the most recent 0.002% of the Universe.
Humans in the year 3000 will have a larger skull but, at the same time, a very small brain. "It's possible that we will develop thicker skulls, but if a scientific theory is to be believed, technology can also change the size of our brains," they write.
Just as our planet existed for more than 4 billion years before humans appeared, it will last for another 4 billion to 5 billion years, long after it becomes uninhabitable for humans. Shichun Huang is an associate professor of Earth and planetary sciences at the University of Tennessee.
More reproduction followed, and more mistakes, the process repeating over billions of generations. Finally, Homo sapiens appeared. But we aren't the end of that story. Evolution won't stop with us, and we might even be evolving faster than ever.
After the dinosaurs died out, nearly 65 million years passed before people appeared on Earth. However, small mammals (including shrew-sized primates) were alive at the time of the dinosaurs.
Human extinction is the hypothetical end of the human species due to either natural causes such as population decline from sub-replacement fertility, an asteroid impact, large-scale volcanism, or via anthropogenic destruction (self-extinction).
But how long can humans last? Eventually humans will go extinct. At the most wildly optimistic estimate, our species will last perhaps another billion years but end when the expanding envelope of the sun swells outward and heats the planet to a Venus-like state. But a billion years is a long time.
Historic growth of world population
500 years BCE it was 100 million, and in the year 0 around 200 million people were estimated to live on Earth. After the Great Famine of 1315–17 and the Black Death in 1350, the world population was around 370 million people and around 1800 it reached 1 billion.
Extending the UN's probabilistic population models, the paper, published in the International Journal of Forecasting, found that our population size in 2300 will likely be between 2 and 26 billion people, with a median projection of 7.5 billion.