HUMAN HEIGHT AND DARWINIAN SELECTION

HUMAN HEIGHT AND DARWINIAN SELECTION

or In defense of the hobbit.

Perhaps this idea struck me when, after purchacing two expensive tickets, my wife and I found ourselves seated behind two quite tall and large young gentlemen at a Manhattan theater. Crane our necks this way and that as best we could, we still could attain only a partial view of the stage, framed by a the men's big shoulders and heads. When we stood at the finale to applaud the actors, they stood too, completely blocking our view. We clapped as we stared at the rumpled butts of these young men, and might have as well been standing facing a brick wall. As we left the theater, I found myself rubbing shoulders (well not quite, perhaps my shoulders were rubbing their elbows) with these two offending over-sized young men, and others who were on average much taller than we were. I have come to the conclusion that in comparison to the present population of young people I am seriously height challenged.

As a man with more than seven decades of observational experience, I can well remember times more than six decades in the past, in the late 1940s. In those days, a guy like me at 173 cm, 1.73 meters, 68 inches, or five-feet-eight-inches tall was just about "average" height. At maturity, I was taller than my paternal grandfather by a few inches, and about an inch taller than my own dad. Pap'a, my maternal grandfather was an inch or so taller than I.

In school, true, I never seriously considered playing basketball, but did shoot hoops with the other kids on the park court and played quite well. I was average height, but not in "tail end" of the bell curve on height that commanded the respect of the neighborhood toughs. To make up the difference I needed strong, fast legs to get me out of altercations with the bigger kids, some of whom in my Brooklyn neighborhood were serious bullies. For fast get-aways, my smaller frame and shorter but strong legs were a distinct advantage. I generally out-distanced the big guys in sprints. But I knew I had to put some distance between me and them fast. To facilitate these escapes, I studied and memorized the terrane and with my size and height I was particularly good at hopping hedges and slipping through breaks in board fences--where they could not easily follow. Thus, in this way, I adapted to being in the middle of the height curve as a boy.

But as I moved on into maturity and middle age I entered into a wider world, where other factors counted more than just how high your eyes were above the ground. Important too, thankfully, was intellectual attainment, sucess, wealth, status, etc. Height decreased in importance during this period of my life. It was OK to be just average--at least in this category. Who cared? But as time went on, and new generations sprung up around me, I have been forced to conclude that among these new cohorts my just-average height-status has clearly diminished into sub-average. Was it me shrinking, or these youngsters getting taller? Now in my seventies, I have had to admit that I am short. Of course, I have shrunk a bit as well, due to the many years of unrelenting gravity, pounding the turf as a habitual jogger, and insisting on walking and carrying a bag to play golf. Over time gravity has compressed those elastic tissues in my skeletal system. But that is expected.

The medical study of stature, termed auxology, is grounded on the assumption that height is and has long been considered one of the characteristics of good health. This assumes that wellness and adequate nutrition and health-care may promote greater stature. But perhaps there is more to it than simply good care and nutrition.

According to my own personal observations the world around me is getting taller. But are human populations actually increasing in stature? And if so, what are the causes? Is there an ongoing spurt in height as a result of a plentiful supply of food in modern industrialized nations? Or is it more than that?

That the stature of populations are in fact altering has been documented by several studies. One of particular interest is that of Professor Joerg Baten an economist and economic historian of Tubingin University, Germany who achieved distinction on his study of the long-term development of human capital and living standards (See: Joerg Baten* "Global Height Trends in Industrial and Developing Countries, 1810-1984: An Overview.") In this report, Professor Baten, and his colleagues at Tubingin University used anthropometric historical means to document changes in human height (measured as you would expect as the distance from the top of head to bottom of feet) from 1810 to 1984. Professor Baten's goal was to use height as a measure of long-term human living standards.

Data included in the report reveal that in almost all countries examined by Baten's study, the trend in human stature is upward. Populations world-wide are growing taller by the decade. Baten (no date) includes a graph which reveals that world average heights (for men) climbed from about 160 cm (5' 3") in 1810 to just about 170 cm (5'7") in 1984, or about ten centimeters or four inches in 174 years (174/20 = 8.7) or an average increase of four inches in nearly nine generations. That is a rate of increase in height of approximately one-half inch per generation. The rate of change that one might actually notice over a human lifetime of between three and four generations. In regard to male heights in industrialized nations (where the population was likely to be less often stressed by food scarcity and presumably have better nutrition and health care) Baten's data indicates that male heights rose from about 166 cm (5' 5") in 1810 to above 178 cm (5'10") in 1984. That is about five inches in nearly nine generations and supports the concept that better nutrition plays a role in height. Baten's data also indicates that only two populations he tabulated do not follow the general upward trend, South Asia and South East Asia populations. Both of these groupings either remained nearly steady over that time or rose only slightly.

Some of Baten's conclusions are the following: Ignoring medical conditions such as gigantism and dwarfism, human populations which share a genetic background and are found in similar environmental circumstances appear to demonstrate similar stature.

Also: Alterations in nutrition caused by extreme poverty, long term warfare, and climatic disruptions may alter adult stature.

Baten also examined the relationship of human height to nutrition and to the gross national product of the states in which the data was collected. And he found that these factors do show some level of correlation.

Baten's data supports my personal observations that our youth are taller than in the past. But my hypothesis is that the changes noted are not simply related to better nutrition or health care (or being umped up with vitamiins) but is a classic case of Darwinian selection. My reasoning is thus: Over thousands of generations human-kind has been subjected to the stress of normal seasonal scarcity (winter food shortages), droughts, as well as prolonged famines related to climatic and other natural variations. Over time, human populations slowly evolved to adapt to nutritional stress by reductions in size and height. Smaller individuals were more likely to survive famines and food stress and live on to reproduce. These, naturally selected, individuals gave rise to generations of smaller, shorter more-efficient individuals better adapted to an environment with uncertain food sources. But times change and besides physical change humans are capable of social and intellectual change. Thus it was that during the Roman and Persian empires and the islamic agricultural revolution of the 8th century as well as industrial revolution of the mid 18th century man discovered new, crops, more-effective ways to produce food and more importantly new sources of energy which changed the human energy balance. No longer did man live on the knife-edge between abundance and starvation. In the post-industrial revolution, when food supply has remained constant for many generations and in some nations the food supply is actually an over abundance, due to cheap energy costs, the stress of food scarcity has disappeared and the natural genetic variability of humans is able to be fully expressed with more taller individuals surviving and reproducing.

THE KUNG! SAN OF THE KALAHARI

Several anthropological studies indicate that in primitive conditions humans lived harsh lives constantly threatened by famine. In the natural state, prior to developing a settled agricultural life style, human labor and effort or caloric output had to equal the amount of calories exploited from the environment to survive and for reproductive purposes, that exploitative ability had to be slightly greater for at least some time of the year. For example, a well-known seminal study of the Kung San (Bushmen) completed in the 1960s by Richard B. Lee ("The !Kung San: Men, Women, and Work in a Foraging Society"). Lee documents the fact that Kung women (with their children in tow) often must complete a seven-mile long walk every several days thorough the Kalahari desert to harvest enough calories from widely dispersed foods such as nuts, (mostly the common mongongo nut), roots and berries for her and her family to survive on a day to day basis. Lee calculates that the women collected the majority of the caloric component of the Kung San diet, while the men, who subsisted on the women's vegetal foods for most of the month, using their hunting prowess and the calories provided by the women to provide the small amount of high quality fats and proteins from their hunting forays on an infrequent basis of about once or twice a month. These small additons of meat were critical for survival. To survive in the harsh Kalahari the !Kung San were under constant natural selection pressure. Smaller individuals were more likely to survive periods of drought and food scarcity. While taller more robust individuals were more likely to be weakened by food shortages and were less likely to survive and more likely to succumb to disease. The result was a diminutive race, only 147cm (4ft 10 in) in stature. Larger and taller individuals would not be able to sustain themselves on the widely dispersed and low caloric content that is exploitable from the Kalahari.

THE CASE OF EDGAR EVANS

The interesting case of Petty Officer Edgar Evans of the Robert Falcon Scott Terra Nova expedition to the South Pole in 1911-1912. Edgar Evans was one of the five men Scott chose to accompany him on the final leg of the ill-fated expedition to the South Pole. Scott chose Evans as one of his five companions probably mostly for his height and girth. He was described as a "huge, bull-necked, beefy man...running to a bit of fat", Evans was taller and heavier by far than his co-explorers. The five man team including Evans reached the Pole on January 17, 1912 to find there a tent with a note in it of the Roald Amundsen Expedition, the rival Norwegian team of explorers who had beat the Scott team there by a mere 33 days.

The return trip back to base camp was a desperate, depressing affair with the knowledge of their failure to be first to the South Pole weakening the will and spirit of the team. The weather turned on them as well. On the way back, their plight became desperate when they lost their way in a storm and missed one or more of their previously deposited food caches. The men were forced to severely ration their food on the return trip. Each night, Scott divided the scarce rations into six equal parts. Unknowingly, due to his disproportionate size relative to his co-companions, Evan's portion was inadequate to meet his greater caloric needs. Providing him with only an equal share, his team mates were in fact slowly starving Evans to death. With his size, he needed many more calories than they did. His one-sixth portion was not sufficient to sustain him and he slowly deteriorated both physically and mentally. During the arduous descent of the Beardsmore Glacier, Evan's condition delayed the team which had to make at least nine miles per day based of the food supplies they had. Evans, often complaining of hunger, and while suffering from low blood sugar and mental disorientation, he critically failed to properly cover his body. The exposure resulted in severe frostbite on his face and hands. In his famine-induced weakened state he stumbled into a crevasse and suffered a mild concussion. He soon became too weak to travel and collapsed on the 16th of January, and died the next day --17 January 1912. Evan's size, which Scott thought would be an asset to the team's effort was in fact a fatal deterrent in circumstances where food was scarce. His body simply required much more calories than his co-explorers...calories that were not available to him--as a result he was the first to succumb to starvation. The team struggled on until March 29, 1912 when, only eleven miles or about a day's march from their base camp and food, they too succumbed to starvation.

HUMANS WERE UNDER CONSTANT SELECTION FOR SIZE

Through almost all of human history, people lived on only the bare minimum caloric intake. Prior to the development of labor-saving technology and agriculture advances human labor was capable of only providing a bare existence. For thousands of years humans survived on just enough calories to survive but no more.

Like all other animal populations humans for thousands of years lived on the knife edge between feast and famine. Each year during the winter when food became scarce, famine stalked the land. Those who did not consume sufficient calories, weakened, their immune systems failed, and they were more subject to disease and were more likely to succumb to the disease and die. As in the case of Edgar Evans, when food stocks declined, it was the smaller, shorter, more lithe i.e. more "efficient" sized humans which were more likely to survive over the winter. Taller larger individuals whose mass required greater numbers of calories suffered disproportionately during times of scarcity. Over time, these food scarcities tended to favor more efficient size individuals who would be more likely to survive the winter famines, or as in the case of the Kalahari Kung! The vagaries of climate and natural scarcity in a harsh region of the earth.

FAMINE--THE CAP ON HUMAN GROWTH

Thus natural annual fluctuation in food availability and quality, and resulting famine kept a cap on human size. Humans tended toward the size that the environment in which they lived permitted. In the nutrient deficient Kalahari, humans were slowly selected to be diminutive. While in more nutrient rich northern Europe the species attained greater height. But as the pressure-cap of famine abated or was removed during the technological revolutions of the industrial age and the age of coal and oil those restrictions on size slowly altered.

TECHNOLOGY REMOVES PRESSURE ON SIZE

As technology aided human production of food, annual famines decreased and eventually disappeared from the scene. Today rather than the threat of famine, food production and excess availability due to the wide availability of coal, oil and other fossil fuels which have supplanted animal and human labor, have advanced to the point that the incidence and threat of famine and food scarcity is gone. (Today, the threat is of too much food rather than too little. Obesity has arisen as the most severe thereat to health rather than famine. Part of the obesity problem is that in the past times of famine humans evolved physiological adaptations to scarce food supplies which increased their food efficiency. They evolved to be food efficient. During periods of food surplus these individuals are predisposed to store fat and become obese.) The evolutionary pressures which had kept a cap on human size have been removed and the human gene pool continues to produce phenotypes of larger individuals with similar frequency as in the past, but, absent famine and annual periods of scarcity, these individuals are able to grow to maturity and reproduce.

The result is that old guys like me claim to see more tall people than they had before. It's true, but disconcerting to average height individuals who have to keep craning their necks upward to speak to the young inefficient giants. We older "hobbits" are proud to be the result of thousands of years of natural selection. We are the efficient ones, that use up less oxygen, less food, and need fewer yards of fabric and leather to cover our nakedness. With the coming crunch of shortages in resources as our world population tops seven billion (this year) and our food, air, water and other resources get scarce, you big fellas will be all looking back at us and giving us credit for being a more "green" and more efficient-sized form of human. And I'm sorry to say by that time, most of us "just average" sized folks will be gone from the scene.

Get the picture?

rjk