The secret of the forest gnomes

Why are there tribes whose members are much smaller than the human average?

A asks in the forum, "The cases where a woman marries a man shorter than her are rare. Height is a genetic trait. And so short men will have children from short women and tall men will have children from tall women.

The short couple will surely have short children and the tall couple will have tall children and God forbid the matter will come back in future generations. And the question arises: Why doesn't the human world slowly divide into groups of dwarves and giants?"

So that's it, dear A. dwarves and giants are simply less successful than us, the average height. There are distinct advantages to being tall, for example our ancestors walked quite a lot and added height means fewer steps are required to cover a distance, in addition tall men are successful among women on the other hand excessive height puts a strain on the heart which is required to pump blood to a greater distance, and the higher the center of gravity the less stability, The load on the joints increases and the risk of falls increases. These opposing pressures cause convergence at a distance less than optimal height. When you compare us, humans, to our friends in the animal kingdom, it becomes clear that the height differences between individuals within the human population, that is, the relative "standard deviation" is very low. When you check the length distributions of animals, it turns out that more than 90% of them are more diverse than us, meaning that there are more "dwarves and giants" among them than we do.

Against the background of this uniformity, the exceptions stand out: human populations whose average height is deep in the lowest percentile among the population of the West. These tribes, scattered in several places in Africa, the islands of Southeast Asia and South America, are called pygmies. The men of the Efe of Zair (Efe), the shortest of the Pegas, stand at an average height of 1.42 meters and the height of their wives is 1.35 meters. Members of other pygmy tribes are slightly taller, but in all of them the men are shorter than a meter and a half and the women are shorter than a meter and 40 centimeters. Since the first meeting with the pygmies was recorded: a "marcade dwarf" brought from Central Africa to entertain Pharaoh Nafrikar about 4500 years ago, the little people pose a challenge to our understanding of the dimensions of the human body, if there is indeed an optimal size why are they so far from it? The simplest hypothesis is that it is the hand of chance: a population found in a small and isolated group reproduces characteristics of the founding fathers. But genetic research shows that pygmies are not a race and have no common ancestor. The different pygmy groups each developed separately on at least 3 separate occasions in ancient history. What is even more strange is the similarity in the environment and the way of life: all are hunters - some live in tropical forests. Our ancestors separated from the jungle-dwelling chimpanzees and crossed the path of human evolution in the open plains of East Africa. The ancestors of the pygmy tribes made, about 50,000 years ago, the opposite route to the southwest and returned to the thicket of the forests. Other groups arrived in their migrations to the forests of Asia and America and something in this new way of life caused them to decline, a phenomenon known as convergent evolution. What, then, is there in the forest that dwarfs its inhabitants?

The first hypothesis concerned the weather: animals of the same or related species tend to be larger in cold areas and smaller in warm areas. We generate heat in the muscles and lose it through the skin - the larger the creature, the less skin area there is per unit of muscle volume and therefore the less heat loss. In the steamy atmosphere of the jungle where the sweat has a hard time evaporating, the small ones are more immune to heatstroke. The problem is that the near neighbors of the pygmy tribes, such as Bantu farmers and herders, are converted to a normal floor, in addition, the pygmy tribes of New Guinea live in a cold mountainous region. Another hypothesis concerns traffic in thickets: in contrast to the plains, where the traffic is usually in a straight path, the inhabitants of the forest are forced to squeeze between thickets: just as a car will catch up with a moped on a highway but lag behind it in crowded streets, so also in the forest the advantage of the shorter ones is revealed in finding free lanes. Another advantage is in vertical movement: the pygmies from the Apa tribe spend almost a tenth of their waking time climbing trees in search of honey-yielding beehives: during this time they are at an average height of 19 meters above the forest floor (the height of the 6th floor of an apartment building) and honey shedding has also been recorded at a height above 50 meters. For those who climb branches it is safer to be light weight and small in size. It is difficult to assume, however, that such a far-reaching change in body structure would occur in order to gain an advantage in climbing or radiating honey: a useful snack but not an important food component in the human diet.

Other explanations are related to the difficulties of life: a forest is a very difficult environment for obtaining food: the fruits are difficult to gather and for hunting animals there are many possibilities of evasion and hiding. In conditions of malnutrition, it is better to be small in size and, accordingly, to be satisfied with little. In Scott's tragic journey to the South Pole, says one of the researchers, the tallest of the group was the first to die even though the food was shared equally.

But the most well-founded theory of the advantage that dwarfism gives to pygmies is based on an accurate measurement of their growth curve. Humans grow fast in the first years of life, then, roughly between the ages of 6 and 12, growth slows down and accelerates again during puberty. There are no big differences in height between the pygmy children of most tribes and the children of the rest of the world up to the age of 12 or so. Pygmas are short because they stop growing much earlier and lose the growth spurt of puberty. Children and boys grow tall as long as the growth disc is maintained at the ends of the long bones in the limbs. At the end of puberty, the hormone estrogen causes this cartilage disc to become a hard bone that will no longer lengthen. It turns out that pygmies reach sexual maturity very early and also become younger parents. According to this explanation, the short stature of the pygmies is not an adaptation to the jungle but is a by-product of rapid maturation. But why exactly did the pygmies benefit from such an acceleration of puberty?

It turns out that humans are simply not adapted to forest life. The life expectancy of pygmies is the lowest of all human populations. Data on life expectancy was collected from 6 such tribes around the world and it ranges from 15 and a half to 24 (for our informants the Hapa people the life expectancy is 16) a significantly shorter life span even compared to hunter-gatherers in open prairies or even near the pole such as aborigines and Eskimos who enjoy 35-45 years Haim. Only about a third of pygmy children get to celebrate their 15th birthday and also the life expectancy of those who survived the dangers of childhood is less than 30 years and in some tribes does not exceed 25 years. It is hard not to doubt the "man's authority over the beast" if, under similar environmental conditions, the large brain, language and culture do not give us a longer life than the chimpanzee. While in other populations there is an advantage for those who postponed the mitzvah pro varbo for a few years and used the time to grow, the pygmies simply do not have a moment to waste. The age of the first pregnancy in the girls of the Aeta pygmy tribe is 15 on average and 5% of the girls of the tribe get pregnant before the age of 13. This is not a pedophilic attack but survival: a mathematical model based on the life expectancy of different groups shows that early puberty is the only way to ensure long-term survival when death is so close.

Well A1' the world is not divided into dwarves and giants but into dwarves and mediums and fortunately for us most of us belong to the second group.

Thanks to Dr. George Perry for his help.