One such cave complex (Kotumsar and Dandak) is situated in Kanger Valley National Park in Bastar district of Chhatisgarh in India. Situated in dense forest, these caves even today require some amount of grit to reach and enter. The hillocks in which these caves are located are made of limestone which is nearly 2500 million years old. The caves have been formed by the gradual dissolution of limestone. Such caves have yet another significant feature, the speleothems or the stalagmites and stalactites formed by the carbonate dissolved in water that trickles inside the caves in drops. Over the years as the water evaporates the precipitated carbonates acquire funny shapes. While at most places in India these shapes are revered by the common men, the geologists look for them for a different purpose. They study the oxygen isotopes in the stalagmites (those which grow from floor towards the roof of the cave) for reconstruction of the palaeo-monsoon. 

Out of these two caves Kotumsar cave is longer and wider than Dandak cave. They are about five kilometres apart in two separate hillocks with Kotumsar cave opening towards southeast and Dandak towards the west. Both the caves open in to dense forest. These narrow mouthed caves require a descent of about 20 metre in Kotumsar and to enter Dandak cave one has to crawl thus making them more mysterious and enigmatic.

The caves are totally dark and one marvels at the ingenuity of the ancient man to enter such caves and use them as abodes. Perhaps they were the safest places to live in without the risk of predators or vagaries of nature!

Presently this area is inhabited by the tribal, the dhurva people. They sustain on an agrarian economy and minor forest produce. Knowing the typical geomorphological and geographical set up geologists, speleologists and archaeologists from various research Institutes get attracted to these caves in search of the clues to the past. One such team consisting of M.G. Yadav and R. Ramesh of the Physical research Institute, Ahmedabad, K. S. Saraswat of Birbal Sahni Institute of Plaeobotany and Prof I.B. Singh of Lucknow University, Lucknow thought it fit to explore these caves. Their exploration was richly rewarded by the find of burnt earth, charcoal and plant remains (both domesticated and wild) in the Kotumsar and Dandak caves.

The scientists found burnt earth on the floors of both the caves. The site indicated controlled fires, as if there was a hearth! Evidence of controlled fires inside the cave and dense forest outside was reason enough for the team to search for more possible evidences of human presence in the caves. Samples collected from 100 and 120 metre depths of Kotumsar and Dandak caves respectively yielded what the inquisitive scientists were looking for. The organic matter collected was subjected to carbon dating.

The samples of Kotumsar gave an age range of 4180 to 7680 calibrated years before present (Cal years BP) and the one from Dandak cave yielded an age of 5042-5318 Cal years BP. It is worth knowing that the ages obtained from Carbon dating are calibrated with the help of other dating methods and the age obtained always indicates 'years before 1950'. This was year in which radiation curves for radiocarbon dating were established. This year incidentally also predates large scale nuclear weapons testing, which altered the atmospheric ratio of Carbon-14 to Carbon-12. The seeds and plants obtained from the depths of the caves convinced the scientists that domestication of plants had already started some 7000 years BP.

Palynological studies (study of fossil plants and pollen) helped to identify three varieties of grasses and two varieties of millets. Grasses and millets still grow in the area and are still collected by the tribal from the forest for domestic consumption. Grains of Foxtail Millets indicated an age of 4300'90 years. In the days of the yore these were important in the economy of the cave men. It is intriguing that in those days man was a hunter and gatherer. The trait of gathering millet seeds and other herbs for sustenance still persists amongst the tribal communities of India. A sample from Kotumsar cave also yielded remains of Sirwari, a sub-succulent pot-herb. The leaves and shoots of which are still eaten by the local tribes. Since the caves are dark, it is apparent that our hunter-gatherer ancestors collected the herbs from the forests around and stored in their safe houses. 

No traces of those ancestors have yet been found in the caves either in the form of their remains or tool, but the evidences, particularly of storing food grains and patches of controlled fires on the surface are enough reason to believe that they thronged the place. Many families must have lived there! 

In other caves like Bhimbetaka near Bhopal cave paintings depict a lot about the occupation of those societies. There are the scenes of war and hunting etc. Such cave art has so far not been discovered in the labyrinths of these caves. One of the main reasons could be says Prof I.B. Singh the constant dissolution of limestone never gave the cavemen the smooth surface required to draw or paint!

What happened to the cave dwellers of Kotumsar and Dandak, where did they go, why did they abandon their abodes? Climate and environment are two factors that have caused rise and fall of several past civilizations. Even today the Indian economy sustains on rainfall. A good monsoon means prosperity and a dry monsoon spells doom for the farmer. Like many other caves the occupants of these two caves were also compelled to abandon them because of lack of availability of food, which of course depended on the rain fall. 

Gathering information about the palaeomonsoons with the help of spelothems is catching up with the scientists globally. Speleothems can be compared with the growth rings of a tree. The rate of formation of these rings depends upon the amount and rate of rainwater entering the cave, the amount of acids and minerals in the rainwater and the temperature and humidity conditions within the cave. In dry periods the growth rings may not form at all but in optimum conditions they may grow a lot. The best part is that these rings retain various oxygen isotopes such as (18O) and carbon (13C) which vary with temperature and rainfall.

Climatologists and geologists in New Zealand have been able to develop the rain fall pattern based on speleothems for the past 15,000 years before present. Similarly Dr. Ashish Sinha of University of Southern California, LA, studied the stalagmite cores from different parts of India, including Dandak caves. The record of the oxygen isotopes recovered from these indicates great variation in Indian Monsoon. His studies indicate solar forcing of Indian/Asian Monsoon variability on decadal to centennial time scale.

Areas rich in monsoon became centres of human settlements and were deserted whenever a drier phase set in. Perhaps it was one of these centennial scale climate changes that compelled the cave dwellers of Kotumsar and Dandak to abandon the caves some 4000 years BP!

May be the cave dwellers set out for greener pastures!