According to a fifth-century midrash, man was created on the first day of Tishrei. The Jewish New Year, in other words, is the birthday of humankind. But whereas in that biblical story man was created 5,782 years ago in one fell swoop (“Vayehi,” or “Let there be”), science demonstrates that Homo sapiens appeared some 200,000 years ago, at the end of a process lasting hundreds of thousands of years.
In fact, this process has not ended. The evolution of the human race continues, and there are scholars who claim that this is happening at a particularly rapid pace, in every one of us.
'In early human societies the transition from infancy to childhood took place at age 3. Today, the transition takes place at age 1 and sometimes even earlier'
The median artery is the one that initially carries blood from the mother to her fetus’ forearm. Later, two other arteries develop to replace it and it usually disappears. Recently, though, researchers discovered that if in the past, cases of the median artery remaining in place were rare, they are increasingly common nowadays.
In the mid-19th century, the median artery was found in only 10 percent of adults, whereas today it is found in 30 percent of those born at the end of the 20th century – a substantial increase for a short evolutionary period. By the end of the present century, researchers estimate, most of humankind will have three arteries in their forearm.
Karl Skorecki, the dean of Bar-Ilan University’s Azrieli Faculty of Medicine in Safed, who studies the influence of evolutionary processes on human health, believes that human evolution is undoubtedly continuing. “The growing population and the rise in the age of parenthood are increasing the possibilities for genetic mutations, which are the underlying engines of evolution,” he says.
'The behavior of young people, who spend a lot of time on social media, is likely to have implications for evolutionary developments'
“Culture also has a great influence on our adaptation to our environment. The behavior patterns of young people, who spend a lot of time on technological devices and social media, are likely to have implications for evolutionary developments, as may migration movements and increases in population density.
“Despite the tremendous success of medications, vaccines and hygiene, despite the relative abundance of food and the unprecedented ability of the individual to control his local temperature, the three major forces of natural selection – infectious pathogens, climate and nutrition – are still highly relevant, as we can clearly see today.”
For Prof. Ze’ev Hochberg of the Rappaport Faculty of Medicine at the Technion – Israel Institute of Technology, Haifa, evolution hasn’t stopped. Instead, it has accelerated.
'For chimpanzees, for instance, and in early man, there was no childhood or adolescence'
“Evolution depends on the environment in which we live, which is currently changing faster than in any other period,” he says. “In a recent study I conducted with Dr. Alina German from Haemek Hospital in Afula, and Prof. Gustavo Mesch of the University of Haifa, we examined the height of people in various countries.
“We found that where there is more stress – for example, in countries with a high level of violence – people are shorter. There is even a correlation between corruption and economic inequality and height. That’s an example of the connection between the environment and human evolution. During the past 150 years, the average height was constantly increasing. However, that’s no longer the case with the past generation. The cultural influence on evolution is faster and stronger today than previously, and this is evident in a variety of features.”
The six stages of life
Cultural influences are also evident in the most basic framework of the course of our lives. “Life history” is an approach that explains the course of our lives from an evolutionary aspect. It was found that humankind has six stages of life that are distinct from one another in biological terms: infancy (from birth to age 1); childhood (up to the age of 5 to 6 in boys, and 6 to 7 in girls); juvenility (which lasts up to age 10 in girls, and age 11 in boys); adolescence (to age 14 for girls and age 16 for boys); emerging adulthood (up to age 24); and, finally, adulthood.
The division into stages of life developed in evolutionary terms for millions of years, Hochberg says. “For chimpanzees, for instance, and in early man, there was no childhood or adolescence. Childhood as a distinct biological period – after the infant has stopped nursing, but before he can be independent to some degree – appeared only 700,000 years ago.”
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Adolescence is also a human innovation, first surfacing 200,000 years ago. “During adolescence, we grow 12 centimeters [nearly 5 inches] a year, compared to 6 centimeters in childhood, and we find this acceleration only in relatively modern man. For other species and earlier human beings, growth was at a constant rate,” Hochberg explains.
A series of studies found that in the seam line between each stage of life and that following it, important characteristics are determined.
“In a study I conducted with Prof. [Kerstin] Albertsson Wikland of the University of Gothenburg in Sweden, it was found, for example, that our height is to a large extent determined in the transition from infancy to childhood,” Hochberg continues. “The living conditions of an infant during the weeks when this transition takes place determine 13 centimeters of his final height – out of the 25 to 30 centimeters that’s the total difference between tall and short people.”
Similarly, he adds, part of the difference between people’s life expectancy is determined in the transition from juvenility to adolescence. “Those who mature late will live longer,” Hochberg declares.
Another Swedish study discovered that what determines life expectancy in men includes, among other things, the living conditions and quality of life during the transition to adolescence. When the conditions are better, sexual maturity comes earlier – accompanied by a certain shortening of life expectancy. In all other stages, good living conditions do not harm life expectancy. “Early maturity means that fertility comes more quickly, which is what interests nature,” Hochberg says. “But this earlier onset comes at the expense of years of life.”
The stages of life, which were determined throughout evolution, continue to change even now, at an accelerated rate.
“Adolescence, for example, underwent a major change in recent centuries,” Hochberg notes. “If 150 years ago the onset of menstruation was at the age of 16.5 on average, today it’s at the age of 12.5. On the other hand, emotional and behavioral maturity is actually later.”
The infancy stage is also undergoing great changes.
“In early human societies, all the children nursed until the age of 2.5 to 3, and the transition from infancy to childhood took place at age 3,” he says. “Today, the transition takes place at age 1 and sometimes even earlier, since there are babies who don’t nurse at all, and some who nurse for half a year to a year (based on the parents’ decision). Incidentally, the transition takes place at an early age even for someone who nurses for three years, because it’s already in our genes.”
Because infancy is shorter, childhood begins earlier. The transition to the next stage remains unchanged, though, so childhood has become much longer. “This shows that the ‘invention’ of childhood was a very big success in evolutionary terms,” Hochberg says.
“Evolution is a random process – and here this random thing was successful. Why? Because when there’s childhood, the mother nurses for two to three years, and then she can have another child, and meanwhile the tribe will take care of the child – or the grandmother, who plays an important biological role in human society. Among chimpanzees, on the other hand, the mother nurses for five years. In other words, until juvenility, and then she can only have another offspring once every six years.
“In other words, the addition of a stage between infancy and juvenility enabled man to have more offspring. Today, infancy has become even shorter and it’s possible to give birth every year. There are some people who do that, and in evolutionary terms they’re actually more ‘successful’ than those who have fewer children.”
'The three major forces of natural selection – infectious pathogens, climate and nutrition – are still highly relevant'
Moving up the adolescence stage, on the other hand, did not lead to its lengthening, since it continues, like before, for about five years for boys and four for girls.
What has lengthened is the next stage, that of emerging adulthood, which begins earlier and lasts as in the past until age 24. Until that age, Hochberg says, there isn’t really adulthood: the sex hormones are different from those in adulthood, as is behavior and decision-making ability.
“It’s a particularly dangerous stage, because although they look mature, these young people still behave in a thoughtless manner. In Africa, it’s clear to members of the Maasai people that at the age of 18 they can play sex games, but won’t marry before the age of 24. Those who marry at an earlier age are actually acting against nature.”
'We found that where there is more stress – for example, in countries with a high level of violence – people are shorter'
There is a good reason for the prolonging of the emerging adulthood stage, he adds: “It’s very complicated to be an adult in the modern world. You have to learn a lot, especially in terms of emotions. If the stage is longer, there’s more time to prepare you for adulthood.”
Cultural changes trump genetic ones
Dr. Oren Kolodny of the Hebrew University also deals with the influence of culture on evolution. “I’m often asked whether human beings have been released from evolution – does natural selection still work? Does “survival of the fittest” still operate on us? It seems as though these are no longer relevant.” But the answer is that evolution is definitely relevant to us. “Diseases, for example, have always been a major selective force,” and repeatedly we find that adaptations that occurred were strongly related to changes in the immune system due to dealing with pathogens. “This is still happening, as we can even even see in the current COVID pandemic. So, evolution in the classical sense continues,” he says, “but it’s not the most important or interesting thing happening in human beings.”
He continues: “The more interesting aspects of our evolution relate to our interaction with the environment and the way we shape it – and how these influence us in return. If you think about the theory of evolution as an attempt to explain the place and trajectory of species in the world over time, then the direction in which humankind is going is dictated far less by genetic changes and far more by cultural ones.”
Genes dictate the translation of proteins, Kolodny says, but they also affect behavior, and behavior determines how we shape the environment.
“In order to understand the place of an organism in the world, I look at its phenotype, which is an expression of the genes. But the nest a termite builds is part of its phenotype just as much as length of its antennae or its hind legs. In the same way, our entire world of beliefs, our language, what we build, is our expanded phenotype, and it changes much more, and much faster, than genetics,” he explains.
The behavioral phenotype of activities like termites building a nest is described by an important evolutionary concept called “niche construction.”
“The classical concept of the evolutionary process is that there’s an environment, and organisms have to adapt themselves to it. Occasionally, there’s an environmental change and then an individual that is more adapted to the new environment thanks to a genetic variant that it carries will be more successful,” Kolodny says. “That’s the basic model for evolution and adaptation.
“But in effect, the situation is more complex and more interesting: Many species not only adapt themselves to the environment, but also change the environment to suit themselves. Beavers, for instance, can build dams that create lakes that are many kilometers in size and change the ecosystem even for a period of 10 generations into the future. This is the source of the idea that there’s a hereditary system parallel to the inheritance of genes – inheriting the environment, or the niche, from my ancestors, which I changed a little more, and transmit to my offspring, who will continue to nurture it and transmit it further: to work the land and preserve it.
A unique case of niche construction is building a cultural niche. For beavers, for example, building dams is an instinctive act. An experiment found that if a beaver hears the noise of running water, it will build a dam even if its cage is dry. “Human beings are also intensively engaged in building niches,” Kolodny says, “but for us, the knowledge is mainly cultural rather than instinctive.”
For example, early humans and Neanderthals who lived up until 50,000 years ago did not build walls at all, says Kolodny, “not even on the level of a few stones to protect them from the wind. Architecture appeared late, although it’s very useful, and it’s not quite clear why this was the case. Part of the answer is that if you aren’t exposed to a cultural concept, you won’t be able to implement it. If you never encountered something built, you won’t build.
“The emergence of the concept of ‘building’ is an Archimedean point. What little children can now do without any problem, our ancestors were unable to do – even though their cognition was similar to ours. It simply didn’t occur to them. So in evolutionary terms, we’re exposed to a physical environment but also a cultural one, and it is no less important.”
A key characteristic of our species, according to Kolodny, is the construction of niches in a way that enables entry into new environments. “That’s how we spread to all the habitats on Earth, and are even thinking of spreading beyond it. Changing the environment is nothing new. For example, in traditional Middle Eastern societies, they began to cut down forests to make room for agriculture thousands of years ago – and that’s what shaped the environment we see nowadays. Today, we’re doing it on an unprecedented scale, some of which isn’t in the best interests of our species.”
Contrary to common belief, Kolodny adds, evolutionary processes do not always lead to long-term adaptation. Even environmental changes that organisms make to their environment might help them in the short term but prove destructive in the long run.
“Predators, for example, are likely to destroy the species they prey upon if the system gets out of balance for some reason,” he says. “A virus, a bacterium or a parasite may be so lethal that they kill all their hosts and thus destroy themselves.”
Human beings are also sometimes pushed into such an activity. Recently, there was a stretch of dry years in the Namibian desert and the hunter-gatherers in the region were forced to strip the bark from trees there, to serve as nourishment. They did so knowing that it would kill the trees, a critical resource for their long-term survival. Human culture is also developing today in a very destructive direction – not for lack of choice, as happened in Namibia, but out of choices made for economic, social and cultural considerations.
“We live in a world that’s no longer very suitable for us,” sighs the Technion’s Hochberg. “We were created in Africa, where day and night were equal in length, and now there’s electricity and we live in the light 18 hours a day. We were created to live a simple life, and we’re living in a world full of stress.
“This has no positive consequences,” he says. “Man today is in a process of deterioration. Up until maybe 50 or 100 years ago, the world in which we lived improved. But in recent decades it has become worse in various ways, and natural selection is accelerating that. Man today as a species is less suited to the environment, which he has created.”