The earth’s climatic system is extremely complex and the mechanisms of climatic processes are not yet completely understood (Rampino et al., 1987).
During the last century, numerous theories relating to climatic change have been advanced. Several experts have emphasized changes in the quantity and quality of solar radiation.
Sunspot cycles, for example, have often been cited as one possible cause of changes in the amount of radiation emanating from the sun. Sunspots vary in an approximately eleven year cycle.
The second theory of climatic change is the astronomical theory. According to this theory, the angle of ecliptic (the tilt of the earth’s axis of rotation from the plane in which the earth orbits the sun) changes in the eccentricity of earth’s orbit and the precession of the equinoxes. Each of these factors varies in a cyclic manner
A third point of view is that climatic changes in the past occurred mainly because of the volcanic activity.
This theory has, however, been refuted as the volcanic eruptions and volcanism cannot persist over millions of years and the climatic changes in the past occurred only over millions of years.
Whatsoever the cause of the climatic change might be, in the early stages of human evolution, the last ice sheets waned some 1.5 lakh years before present (B.P.).
It was after the last glacial phase that environmental change occurred relatively rapidly and varied considerably on a global basis.
Overall, climatic amelioration ensued as ice sheets retreated in high and higher-middle latitudes to approximately their present position. As a result, ecosystems became re-established in regions that had been previously covered with ice.
This period also witnessed tremendous changes in the development and activities of human communities (Homo sapiens) began to emerge as a dominant force in environmental systems. It was during this period that the domestication of plants and animals was started.
The environment got significantly modified when man started making and using stone as a tool. This stage in known as Homo habilis.
As stated in Chapter 2, the earliest tools were made of stone and it is because of this reason that the earliest cultures are known as Palaeolithic (Old Stone Age). The Stone Age continued up to about 10,000 years B.P., when man started making copper tools.
The copper, bronze, and iron tools and implements developed in later pre-history served only to intensify the process of domestication of plants and animals which began around 10,000 years B.P. Man started to convert the ecosystems into agro-ecosystems, which ultimately led to the agricultural system of today
Hunting and gathering remained as the dominant economic activity of Homo sapiens during the Palaeolithic, Mesolithic and Neolithic periods. Hunting and gathering are being practised even today in many parts of the earth.
The ancestors of man during the Palaeolithic period might have relied on local food resources for their sustenance. In fact, the history of that period is based on conjecture. In the Palaeolithic period, scavenging would have been one form of animal exploitation.
Scavenging and hunting require different skills: the former is more opportunistic while the latter is much more planned operation.
There is hardly any convincing evidence to prove that Palaeolithic groups had a lasting effect on their environment as the Mesolithic and Neolithic peoples undoubtedly exerted. It may, therefore, be safely conjectured that during the Palaeolithic period humans were integral rather than dominant components of the ecosystem (Berger et al., n.d.).
Mesolithic is a transitional period between the Palaeolithic and the Neolithic periods. Presumably, there were unprecedented social and ecological pressures that instigated exploitation of the forest expanding environment. The tools of the Mesolithic period are different in character to those of the Palaeolithic period. The Mesolithic people used various deer, badger, fox and numerous birds for their food.
Around 10,000 years B.P., the Neolithic period was started. It was during this period when man domesticated plants and animals. The emergence of agriculture has been regarded as ‘revolutionary’. Obviously, it was a very important development in the human history.
The start of agriculture provided a more reliable food resource. This may have enabled the development of permanent settlements, and higher population to be supported.
The development of agriculture played a dominant role in the development of human communities and resulted into significant environmental changes.
The natural ecosystems were transformed into agro-ecosystems. With this development, Homo sapiens started to control the ecosystems more vigorously.
As stated in the preceding paras, before the domestication of plants and animals, man was in the hunting stage. Presumably, humans recognized that some animals and plants were more useful than others as sources of food and that it was preferable to ensure an adequate proximal food supply rather than have to engage in relatively haphazard foraging and hunting (Zohry and Hopf, 1988).
Thus, a major turning point in human and environmental history was the domestication of plants and animals. The agriculture led to major changes in social organization and which underpinned some of the most powerful ancient civilizations.
According to Davis (1987), the most important animals, i.e., sheep, goats, cattle and pigs were domesticated in the early part of the post-glacial period, between 8,000 years B.P. to 10,000 years B.P. in the South-West Asia.
South-West Asia was also the centre of domestication of sheep, goats and dog. The transition from hunting and gathering food procurement strategies to permanent agriculture the domestication of plants and animals brought substantial changes in the environment. The introduction of domesticated species provided a food source that supplemented natural plant and animal resources.
In this sense, species diversity was increased, but as clearance of natural vegetation was undertaken to make way for arable fields, species diversity, at least locally, decreased. Geomorphic, pedological and hydrological systems may also be radically altered even cultivation replaces natural vegetation growth.
It may be seen from that the metal tools and technology was started with the use of copper. The copper tools enhanced the ability of humans to manipulate their environment.
The copper age was followed by the bronze and iron ages. With the metal technology animal and plant technology became more popular and crop production system became more efficient. With the metal tools and technology man started becoming the master of the environment.
Precisely when and how metal-working technologies were originally developed is far from clear. According to Mellart (1967), there is evidence of lead smelting as early as 8,000 years B.P. at Catal Huyuk, a settlement that developed in Central Anatolia (Turkey) where Neolithic agricultural practices were well established.
The metal technology began in the area between the Black Sea and Caspian Sea and the Persian Gulf where copper ores are widespread (Saffer, 1987). According to Moore (1985), copper culture originated in Northern Jezireh and Assyria around 7,000 years B.P. and spread later into the Levant (Asia Minor).
The metal technology helped in the expansion and intensification of agriculture. The ability to manipulate the environment did not develop trouble-free.