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domestication of plants and animals, probably because the warmer, wetter weather made farming possible.

Although many people view the current world's huge population with alarm, most ecologists take the size of the population of a species as an indicator of its fitness. By this criterion, the domestication of plants and animals improved greatly Homo Sapiens fitness. This testimony is not the place to discuss the capacity of the globe to sustain the number of people expected to populate the world in the next century, but certainly anything that produced greater numbers of people thousands of years ago must have been beneficial for mankind.

Over history the number of humans has been expanding at ever more rapid rates. Around 25,000 years ago, the world's population may have measured only about 3 million.17 Fifteen thousand years later, around 10,000 B.C., the total had grown by onethird to 4 million. It took 5,000 more years to jump one more million, but in the 1,000 years after 5000 B.C. it added another million. Except for a few disastrous periods, the number of men, women and children has mounted with increasing rapidity. Only in the last few decades of the twentieth century has the escalation slowed. Certainly there have been good times when man did better and poor times when people suffered

although in most cases these were regional problems. However, as the following chart shows, in propitious periods, that is, when the climate was warm, the population swelled faster than during less clement eras.

This chart is based on a paper by economist Michael Kremer who argues that, until the Industrial Revolution, existing technology limited the size of the population.18 As innovators discovered new techniques and invented new tools, more people could be fed and housed and the population expanded. Moreover, the greater the number of people, the more innovations would be hit upon. He assumed that every individual had an equal but very small probability of uncovering a new technique or device and that the probability of being an innovator was independent of the size of the population. Therefore the number of inventions would be proportional to the number of people. Thus as the world population expanded slowly at first the rate of technological innovation escalated and hence the rate of growth of the population that could be sustained. Only in recent times has technological change become so rapid that it has run ahead of population growth, leading to a rising standard of living, which in turn has reduced the birth rate.

17Kremer [1993]: 683. 18Kremer [1993]: 681-716.

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Kremer's hypothesis signifies that for most of history the rate of population growth should be proportional to the size of the population. To link his model and data with climate change, I started with his estimate of the world's people in 10,000 B.C. and calculated the rate of growth of the population over the next 5,000 years. For each subsequent period, I also computed the rate of increase in numbers of people. Comparing these expected rates with actual growth revealed eras in which the number of humans has expanded faster than predicted and periods during which the world's people has grown more slowly. The chart then shows the centuries in which the growth rate of the globe's populace has exceeded or fallen short of the rate expected under this simple model. As can be seen, warm periods have done considerably better than cold periods in terms of human expansion. The warmest period since the end of the last Ice Age produced the highest rate of population growth compared to what would have been expected — in this era agriculture was spreading. Moreover, the Mini Ice Age, which saw the coldest temperatures in the last 10,000 years, underwent the slowest relative population expansion. This chart demonstrates that mankind has prospered in warm periods and the hotter the better!

Another measure of the well-being of humans is how long they live. The life of the hunter-gatherer was not as rosy as some have contended. Life was short skeleton remains from before 8000 B.C. show that the average age of death for men was about 33

and that of women 28.19 Death for men was frequently violent, while many women must have died in childbirth. Since women died so young, they had only around thirteen years in which to bear children. Anthropologists have estimated that on average they could have given birth to less than five live babies, assuming that they bore a child every 22 months.20 An infant and childhood mortality rate of about 60 percent would have kept the population stagnant.

Table 1 below shows some relevant data. The warmest periods, the Neolithic, Bronze Ages and England in the thirteenth centuries enjoyed the longest life spans of the entire record. The shortening of lives from the late thirteenth to the late fourteenth centuries with the advent of much cooler weather is particularly notable. Moreover, the rise in life expectancies during the warm period could easily explain the population explosion that took place during that period.

Good childhood nutrition is reflected in taller adults. Skeleton remains collected over wide areas of Eurasia from the period when roving bands shifted from eating large animals and a few plants to smaller prey and a much wider variety of foods attest to a decline in height for both men and women of about five centimeters (two inches).21 The shorter stature came at the end of the Ice Age when large animals were disappearing. Some archaeologists have found that average age of death for adults also declined during this transitionary period.22 Studies of bone chemistry from Middle Eastern skeletons indicate a reduction in meat consumption. The new diet although more dependent on grains, fruits, and vegetables must have been less nutritious than the old. As large game animals disappeared with the end of the Ice Age, humans widened the variety of plants in their diet, increasingly consuming vegetable matter that they had ignored for thousands of years either because it was less nutritious, more difficult to secure and process, or less tasty. Table 2 on heights, however, signifies that food was more plentiful and better during the medieval Period than during the mini Ice Age.

19Boserup (1981): 36-37.
20 Boserup [1981]: 38.
21 Cohen [1989]: 112.
22Cohen [1989]: 113.

Table 1

Life Expectancy at Various Periods
Mesolithic people in Europe, ca. 8000 B.C.

Neolithic, Anatolia, ca. 6000 B.C.
Bronze Age, Austria, ca. 2000 B.C.
Classical Greece, ca. 500 B.C.
Classical Rome, 100 B.C.-A.D. 300

31.5

38.2

38

35

32

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23-558 96-6

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Modern World

1952-1954

70"

Source: Lamb [1977]: 264 from Bergthorsson [1962].

The First Climatic Optimum Around 9,000 to 5,000 years ago the earth was much warmer than today; perhaps 4°F hotter, about the average of the various predictions for global warming after a doubling of CO2.23 Although the climate cooled a bit after 3000 B.C., it stayed relatively warmer than the modern world until sometime after 1000 B.C., when chilly temperatures became more common. During this Climatic Optimum epoch, Europe enjoyed mild winters and warm summers with a storm belt far to the north. Not only was the country less subject to severe storms, but the skies were less cloudy and the days sunnier.

Notwithstanding the less stormy weather, rainfall was more than adequate to produce widespread forests. Western Europe, including parts of Iceland and the Highlands of Scotland, was mantled by great woods.24 The timber, until average temperatures dipped temporarily for about 400 years between 3,500 B.C. and 3,000 B.C., consisted of warmth-demanding trees, such as elms and linden in North America and oak and hazel in Europe. Not only did Europe enjoy a benign climate with adequate rainfall, but the Mediterranean littoral, including the Middle East, apparently received considerably more moisture than it does today.25 The Indian subcontinent and China were also much wetter during this Optimal period. 26

Compared to cooler periods in the last few thousand years, the Sahara was much wetter and more fertile during the Climatic Optimum.27 Cave paintings from the epoch depict hippopotamuses, elephants, crocodiles, antelopes and even canoes.28 The water level in Lake Chad about 14° north of the equator in central Africa was some 30 to 40 meters, that is, 90 to 125 feet higher, than it is today, indicating much greater

23Lamb (1988): 22.

24Giles, [1990]: 133.
25 Claiborne [1970]: 324.

26Lamb (1982): 120.

27Lamb [1988]: 21.
28 Giles [1982]: 115-116.

precipitation. Ruins of ancient irrigation channels in Arabia, probably from the warmest millennia, derived their water from sources well above current water supplies, indicating a wetter climate.29 With the cooling that started after 3000 B.C., North Africa dried up and the abundance of life disappeared.

As already mentioned, the invention of agriculture coincided with the end of the last Ice Age and the melting of the glaciers. Archaeologists have found the earliest evidence for husbandry and farming in Mesopotamia around 9000 B.C.30 The domestication of plants appears to have occurred around the world at about the same time: from 10,000 YBP to 7,500 YBP.31 Planting of wheat and barley began in southwest Asia between 8000 B.C. and 7000 B.C. Food production in China extends back at least into the sixth millennium B.C. In the Americas domestication of some grains and chili peppers dates from between 7000 B.C. and 6000 B.C.; anthropologists have documented maize in the Tehuacan Valley by 5700 B.C. and production may have started earlier. In South America the evidence suggests that domestication of two species of beans and chili pepper as well in the Andean highlands arose 8,500 years ago. Domestication of cattle occurred in the Sahara about 8,000 years before the present.32

The development of agriculture and the establishment of fixed communities led to a population explosion and the founding of cities. Agricultural societies produce enough surplus to support such urban developments, including the evolution of trades and new occupations. A large community could afford to have specialists who made farm tools, crafted pots, and traded within the village and between the locals and outsiders. The people in today's Palestine established the first known city, Jericho, and thus the first step towards specialization which lies at the heart of economic advancement — around

8000 B.C.33

In Europe, the Optimum period produced an expansion of civilization with the construction of cities and a technological revolution. The Bronze Age replaced the New Stone Age.34 The more benign climate with less severe storms encouraged travel by sea. Trade flourished during this warm period. People from ancient Denmark shipped amber along the Atlantic coast to the Mediterranean. As early as 2000 B.C., the Celts apparently were sailing from Cornwall and Brittany to both Scandinavia and southern Italy. Astrological monuments built around this time, such as Stonehenge, indicate that the

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