Livestock in Guns Germs and Steel: The Negatives

Livestock have contributed to human society in a number of ways, both good and bad. “Guns, Germs, and Steel” chapter Lethal Gift of Livestock dealt with some of the negative consequences of keeping livestock in such close proximity. Also, it considered what diseases are, and why they make us ill. As well as why diseases have been spread more effectively in highly populated settings and as a result of the development of agriculture. It also tried to give an explanation for the almost one-way transfer of diseases for the Old World to the New World.

Epidemic diseases tend to produce no cases for a long time, then there may be a wave of new cases, followed by no more cases again for a time. Since many of these diseases are restricted to humans, microbes causing these diseases are not normally found in the soil or other animals. They spread quickly through a population resulting in an entire healthy population becoming exposed with the infected person either recovering completely or dying within a short period of time.

Those who recover develop antibodies that prevent becoming ill with that disease in the future. Some humans may have a genetic advantage that makes them resistant to a certain pathogen. In epidemic those with genetic resistance are more likely to survive and pass their genes on to future generation. This allows for populations to become better protected against a disease as a whole. However, many of these microbes have been able to evolve allowing for resistance which has resulted in a continuous battle between us and microbes.

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To sustain epidemics, microbes need a human population that is quite substantial and live in close enough proximity to continue the spread of the disease. These diseases, called crowd disease, need dense populations and have come about only since the rise of agriculture in our society. Agriculture is able to support larger populations which has allowed for cities and urban areas to develop gradually over time. Many early cities had horrible sanitation and were breeding grounds for infectious diseases. Many crowd diseases that never could have previously occurred were able to evolve from animal diseases and thrive in these cities. Throughout history people have acquired microbial infectious diseases from animals. Most are relatively harmless and last a few days while others are much more serious. The major infectious diseases of human society have been smallpox, flu. malaria, measles, plague, cholera, and tuberculosis, all of which have evolved from diseases in animals. Humans and animals in many instances live in very close proximity to each and are in contact with each others microbes on a regular basis. Some people even live and sleep close to animal feces, urine, and other bodily fluids. Many of these animals have already been afflicted by epidemic diseases just waiting to evolve and possibly infect humans.

Epidemics have played a substantial role in shaping human history. This can be no more evident than to look at the Europeans conquest of the New World. Many of the people living in New World lived in much less dense populations and had much less contact with domestic animals than that of Europeans. Therefore, they had never been exposed to many of the so-called crowd diseases and had no immune or genetic resistance to them. Epidemics were then able to be spread by Europeans and cause devastating effects among the native people. While it is estimated that there was a 95% decline in the Indian population in the centuries that followed Columbus reaching the Americas, it is thought that not a single deadly disease was brought from the New World to Europe. This may be the result of there not being animals in the New World able to give their diseases to humans. Another reason for this may have been that populations did not become dense until much later, resulting in no formation of epidemic crowd diseases. Only certain diseases are able to survive or evolve in small isolated populations. Chronic and nonfatal infections that are able to survive outside the human body are able to last in a smaller population.

I found the reading to be very informative and thought provoking. I previously had no idea that so many microbial diseases evolved from animal diseases to now infect humans. I also learned about the spread of disease to the Americas. I could not believe the incredible numbers of natives that were killed as a result of epidemics. I knew lots of people died, but not numbers such as in Mexico where the population dropped for 20 million to about 1.6 million. Overall I enjoyed the chapter and would consider reading more or even the rest of the book, if I didn’t have organic chemistry.