15 November 2022 is a milestone for mankind, because on this day the global population touched eight billion. Just 70 years ago, which is the lifetime of a normal human, we were only 2.5 billion. In AD one, the total population of the world was less than a third of a billion. So how did this expansion of numbers come about?
Human beings are not particularly fast, strong or agile. Our senses are also weak as compared to domestic animals and pets. Instead, big brains and the complex social structures on which they rest are the secrets to our success. This gives us an opportunity to change the rules of the game of evolution that govern the fate of most species, helping us to shape the environment in our favor.
But it also had many unintended consequences, and now we’ve upped the game to the point that human-driven climate change has put millions of species at risk of extinction.
Understanding Population Growth Legend has it that the king of Chemaksheri, which is in modern India, was fond of playing chess and challenged a traveling priest to a game of chess. The king asked him what prize he would like if he won. The priest said that he wanted some rice in return for the victory. But the priest had a condition that the rice should be counted in a precise way, one grain in the first square of the chessboard, two in the second, four in the third, and so on. The king thought it appropriate and the game started.
Baji Raja lost, so he asked his servants to reward their guest according to the condition. There were 255 grains in the first row of eight squares, but by the end of the third row there were more than one crore 67 lakh grains. The king offered another reward instead: asked to give up to half of his kingdom. Till reaching the last square, he needed so many grains of rice, whose weight would have been about 210 billion tonnes. Raja understood this method of exponential growth after suffering huge losses.
In the beginning our genes – Homo – started in class one about 2.3 million years ago. We originated from small, scattered populations along the East African Rift Valley. Genetic and fossil evidence suggests that Homo sapiens and our Neanderthal cousins evolved from a common ancestor, possibly Homo heidelbergensis. The brain of Homo heidelbergensis was slightly smaller than that of modern humans.
Neanderthals had larger brains than us, but the areas devoted to thinking and social interactions were less developed. When Homo heidelbergensis began to travel more widely, the populations began to interchange. African ancestry gave rise to Homo sapiens, while migrations into Europe around 500,000 years ago created Neanderthals and Denisovans.
Modern humans living outside of Africa typically have about 2 percent Neanderthal DNA. It is close to zero in people of African background. If unchecked, all populations with higher birth rates than deaths grow rapidly. Our population does not double in each generation because the average number of children per couple is less than four. However, the pace of development is accelerating at an unprecedented rate. Those of us alive today make up 7 percent of all humans that have existed since the origin of our species.
Why are not all species thriving?
Biological interference usually puts brakes on population growth. The population of the strong increases and the number of the weak decreases. In this way, when viruses and other disease agents spread in the population, they destroy them. Or rapidly changing environments can reduce the number of once-flourishing species and groups. Charles Darwin, or before him the 18th-century scholar Thomas Malthus, also thought that limiting human numbers might be difficult.
Malthus believed that our growing population would eventually outstrip our food production capacity, leading to mass starvation. But they didn’t anticipate the 19th- and 20th-century revolutions in agriculture and transportation, or the 21st-century advances in genetic technology, which have helped us produce more food around the world, though in some places. Our intelligence and ability to make tools and develop technology helped us survive most of the threats our ancestors faced. Humans reached space exploration within about 8,500 years of making metal tools.
Now we are fast moving towards a problem. The United Nations estimates that by 2050 we will be around 10 billion. One consequence of these huge numbers is that even small changes in our behavior can have huge effects on climate and habitats around the world. The growing energy demand of each individual today is twice that of 1900.