A Struggle for Survival

Becoming Human Was a distinct advantage to our prehistoric ancestors. While animals lost up to 80 per cent of their offspring at or shortly after birth, human beings were able to raise 70-80 per cent of their children. Human beings were also occasionally able to live beyond their reproductive years - a very unusual occurrence in animals - and this lengthening of life proved a human adaptative change of major importance.

Our primitive forebears probably suffered fewer diseases than we in modern industrialized societies do. However, early hunter-gatherers were prone to chronic diseases, caused by organisms that can survive within individuals and be passed (through touch, sneezing and breathing or through infected food) to other members of a group - the types of illness afflicting apes and other primates today. Top of the list are various bacterial infections and invasions of intestinal protozoa (including some causing dysentery). A number of viruses, herpes among them, are also considered causes of ancient human infections, as are intestinal worms.

Accidental' infections from organisms that normally complete their life cycles in animal hosts were picked up by handling wild animals, butchering and eating them. Hunters were exposed to rabies, toxoplasmosis, anthrax, tetanus, trichinosis and many other illnesses. The environment was also hazardous: the African trypanosomiasis parasite carried by tsetse flies gave sleeping sickness; ticks passed on viral diseases; anaerobic bacteria in the soil caused, among other things, gangrene and botulism.

Because organisms responsible for chronic diseases were continually present in the body, human beings gradually developed immunity and their effects became relatively mild.

Accidental infections - which only occasionally afflicted human beings who, thus, were unable to develop immunity - could, though, be quite devastating.

From the evidence, it seems unlikely that diseases. unknown today affected these early societies. How-ever, some illnesses that are now quite mild may have been extremely virulent.

A Hard And Violent Life

The earliest nomadic tribes were, however, surprisingly healthy - tall and with good teeth. Men lived on average to 35, while women died about five years earlier, This difference was due not only to stresses of pregnancy and dangers of childbirth, but also to women's probable responsibility for shifting camp, carrying burdens, collecting food and cooking.

Endemic diseases do not account for the short lifespans of these people, only their hard nomadic life, the climate and warfare. At one site on the Nile, the archaeological evidence of projectile wounds suggests that almost half the population died violently.

In the Mesolithic period (c.8000 BC), as these early peoples began the transition to more settled communities, humans seem to have become shorter. The reason may have been a less nourishing diet, but it is also probable that new endemic diseases were beginning to have an impact, especially those causing anaemia, such as malaria and hookworm. It is also from this time that the first evidence of thalassaemia is found - an inherited adaptation of the red blood cells that acts as a protection against malaria.

Settling Down

By about 5000 BC, many wandering nomads had settled into communities. Initially, this promoted health and longevity, especially among women, as the stresses of migration were reduced, and it was far easier to care for the sick. There was a more certain food supply, too, and people were increasingly able to develop immunity to common infections. However, settling also had major health disadvantages. Increased trade brought more diseases.

Permanent houses made their spread more likely, as did the accumlation of human waste and the closeness of domesticated animals. Rats and other disease-carrying animals were attracted to refuse; and people staying in one place were constantly reinfected by parasites, such as the blood flukes responsible for schisto-somiasis (bilharzia).

As land was cleared for agriculture, non-human primates lost their habitats. These animals were the primary hosts of mosquitoes, and the malarial parasites and yellow fever viruses they carried. All these now preyed on humans who often chose to settle near marshes and streams where mosquitoes breed. Malaria, in particular, had an immense influence on the future growth of societies and cultures.

Neolithic and early Bronze Age farmers were still not as tall as their Paleolithic ancestors had been - indeed, only today, and then only in well-off Western societies, has the human frame returned to the stature of that time. Nutrition was not particularly good - the Neolithic diet consisted mainly of cereals, and people ate only 10-20 per cent as much protein as their forebears had.

As settlements became more densely populated after 2000 BC, epidemics of childhood diseases became possible. Living cheek by jowl also undoubtedly led to personality clashes and depression - the first signs of modern stress.

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