Post Glacial Climate and the Rise of Human Cultures and Agriculture
Human Dispersal Patterns
The dispersal patterns shown in the diagram may best be explained in terms of human response to ecological changes.
The dispersal of early hominids (see our previous lecture notes)
The first hominids evolved in savanna environments similar to those of East Africa today. These savannas are characterized by high seasonality which influences the distribution of plant and animal biomass. This would have provided the resource base for early hominids. This seasonality is a very important consideration because there are very large differences in the amount of food resource available between wet and dry seasons. Also important is the fact that such environments have large populations of ungulates (hoofed animals) that range in these environments seasonally.
If we look at primates today that inhabit this type of environment we see that they have "wet" and "dry" season food procurement strategies. It may be that when the season is wet there is plenty of plant food available. However, when the season is dry and there is very little plant material available, early hominids developed a strategy to procure animal food to supplement their diets.
They would have found animals around water holes during the dry seasons. Thus this hunting strategy would have reduced the competitive pressure among individuals since they did not have to compete for the meager plant resource. This would have given the hominids a ecological advantage for survival.
The advantage of omnivore and the hunting strategy probably provided early hominids the survival success needed to migrate into the warmer temperature zones including the Mediterranean Europe.
One important observation is that there is little evidence of human occupation in Europe during the warmer interglacials. It has been suggested that the reason for this is that the hominids were not as well adapted to wooded forest environment that prevailed during these warmer phases. Rather, the expansions of humans occurs during the colder phases of climate when the forest retreats and open grasslands are dominant.
dispersal of modern hominids into the Americas
Hominids did not arrive in the America until very recently. In North America this appears to be about 20 thousand years ago. the most likely explanation is that modern man migrated across the Bering Straits during the last ice age when sea level was low enough to expose a land bridge between Asia and North America. Thus climate change had a major effect on human evolution.
This is an important observation because one might ask why the humans did not migrate sooner.
Furthermore, the beginning of the present interglacial saw the migration of humans into wooded environments which had been avoided in all the previous interglacials.
Scientists conjecture that there must have been unprecedented social and /or ecological pressures that instigated exploitation of these expanding forested environments .
Vegetation Changes
Vegetation records show that the climate was warming in a sequences of steps following the end of the last glacial, 12 thousand years ago. This is shown in the pattern of vegetation changes shown in the diagram above.
It is possible that population pressures ensued as the flora and fauna, to which Paleolithic groups had adapted, began to diminish.
Mammal Extinctions
By 10 thousand years ago large numbers of the animal groups present during the Pleistocene had gone extinct.
In North America a total of 33 genera, 73.3% of the animals had gone extinct. This included the Shasta ground sloth, Jefferson's ground sloth, sabre toothed cats, giant beaver, North American camel, and the mammoth and mastodon.
Similar extinction occurred in South America, Australia, Northern Europe and Africa.
Remember, the open grass lands were shrinking as the ice age came to an end. The open prairies were restricted to portions of the central American plains. Thus, much of the habitat area needed by the larger roaming animals was becoming increasingly restricted. This forced these animal groups into restricted environments that perhaps made them more easy targets for hunting humans.
The link to human hunting is circumstantial. But the fossil record (see Rancho La Brea for example) seem to show that most of the extinctions occurred rapidly around 11 to 10 thousand years ago, closely coinciding with the occurrence of humans in North and South America.
The actual date of human arrival in the Americas is controversial but there are good fossil dates that man was here by about 13 thousand years ago, or about 2 thousand years before the disappearance of the larger mammal groups.
Climate change could certainly have contributed to the disappearance of the mammals but the fact that the mammals had survived many previous glacial/interglacial transitions seems to favor the Human hunting idea.
So, what role could Man have had on climate and on the environment?
-The ability of hominid to use, and later modify, their environment more effectively than their predecessors probably began when they learnt to make tools about 2 million years ago. The earliest tools were made of stone and it is for this reason that the earliest cultures are known as Paleolithic (old stone age). The practice of stone tool manufacture has dominated the history of human beings since it is persisted until metal-sing technology was developed only 9 thousand years ago.
-Numerous innovations occurred as food-procuring strategies became more calculated and sophisticated.
-Deliberate herding of animals during the later Paleolithic and Mesolithic (middle stone age) periods culminated in the domestication of both plans and animals that led to permanent agriculture during the neolithic (new stone age).
-However, perhaps one of the most important steps in human evolution that was to alter the environment was the development and extensive use of fire. Although there is evidence that fire was used earlier by earlier humans it was the use of fire by late humans in conjunction with more specialized foraging and a more sedentary existence that was the precursor to agriculture. Some scientists believe that the use of fire lead to environmental degradation and this would have put additional pressure on resources. Ultimately, the increased pressure would have lead to more sophisticated food-producing rather than food procurement strategies.
Development of Agriculture
-The development of permanent agriculture was perhaps more important to the history of environmental change than perhaps any other technological innovation. This development may be thought of as occurring gradually.
In the early post glacial period, around 10 thousand years ago, we have good evidence that humans had begun to domesticate animals. The first domesticated animal was the dog, a descendant of the wolf. It appears that the dog was never a food resource but always used as it is today for herding, hunting and perhaps guarding.
Sheep, goats and cattle and pigs were the first to be domesticated.
Mobility was most likely reduced as the populations of hunting animals was reduced. This lead to the earliest strategies of herding and plant domestication. There is some evidence to suggest that plant domestication preceded animal domestication.
While the development of agriculture and herding may be in part, the consequence of environmental changes following the last ice age, the development of metallurgical technology is probably not close coupled to climate change. Therefore, this will not be a discussion for this class. However, it is important to recognize that the development of this technology did have important consequences on the environment. Certainly, in the context of the Industrial Revolution, and its potential impact on climate, the development of metallurgical technology can be viewed as important step in the environmental history of the Planet Earth.