ALL Food is GMOs:
There is much public concern over so-called "genetically modified organisms" (GMOs). However, as discussed in Diamond, all our crops and livestock are genetically modified from their wild ancestors by means of artificial selection (and in the case of at least some crops, fantastically so!).
The wild precursors of livestock typically shared certain key traits that made them ammenable to domestication:
Not all descendants of the initial crop precursor are necessarily selected for in the same way. For example, different descendants of the wild Brassica oleracea were selected for different favorable traits, resulting in the great diversity of the crops produced from the one species: broccoli, cauliflower, Brussel sprouts, kale, cabbage.
In another case, wild teosinte plants were modified through domestication to produce maize (corn). And yet another, wild bananas were bred into startchy cooking plantains (which are seedless and require human cultivation to propogate) in prehistoric times, and thence into the sweet yellow varieties only in 1836! (A plantain grower in Jamaica found a sweet yellow mutant, which is the ancestor of all the modern sweet varieties. Incidentally, because they are asexually produced, banana crops are extremely susceptible to disease (all individuals have the same level of susceptiblity to any given germ), and periodically whole strains of sweet bananas go extinct. The Cavendish banana--the one we all grew up with--is currently under attack and banana farmers are trying to develop new strains.)
In the supermarket era, new traits have been conciously selected for in addition to the traditional ones:
The Green Revolution: name given to mid-20th Century international programs to develop new strains of crops (esp. rice) and new breeding and planting strategies to feed the developing world (esp. Asia). Brought industrialized farming techniques (including extensive use of nitrogenous fertilizers; petroleum powered farm equipment; etc.) to developing nations. On the one hand, it ended mega-death (1 million or more fatalities) famines that used to hit greater India, southeast Asia, China, etc., during earlier periods. On the other hand, it resulted in biodiversity and soil loss, increased air pollution (including GHGs), decreased water availability and quality, dangerous population increases, and decreased quality of human health in some of these regions.
New Biotechnology Traits: since the 1990s direct gene manipulation of crops became possible (i.e., you didn't have to wait for the mutants to show up). Many of the new biotech crops had elaboration of the previous types of favored traits. However, some the additions were new, including but not limited to:
Diseases, Plagues, and the Extended Phenotype:
Some diseases are genetic, some are caused by abiotic environmental factors (e.g., UV or other radiation; various chemicals; etc.), and many by disease organims (pathogens including viruses, bacteria, single-celled eukaryotes, fungi, and animals). Pathogens produce symptoms, which we think of as malfunctions of the victim's body but which are best understood as transforming the systems of the host (victim) into the extended phenotype of the pathogen. That is, the environment of the body of the organism and the cells of its body are transformed into a factory producing more copies of the pathogen and as a vector to transmit these new copies. Many symptoms that involve outpourings of liquids or aerosols from the body are not the victim's body going wrong: they are the pathogen transforming the host into a means to spread the pathogen's babies.
(Some symptoms (such as fevers) are actually the host body's reaction to create a non-viable environment for the pathogen.)
A pathogen has a tradeoff between virulence, transmissibility, and persistence:
Plagues are pandemics (outbreaks of infections diseases over large regions and large populations) of lethal diseases. Some of these are among the worst disasters in human history:
Where do (most) traditional diseases come from? Majority are evolved from the diseases of farm animals (measels from rinderpest; smallpox from cowpox; influenza is a disease of pigs and poultry as well as people; etc.) People living in close contact with animals may get infected by the animal's pathogens. Some of these pathogens eventually mutate to be viable in human host.
Emergent Diseases of the 20th and 21st Centuries:
Vaccination: Of ancient origin, but highly promoted in Europe and the West by Edward Jenner in the 1770s. The principle: use a weak or killed version of the virus, or a closely related form, to trigger an immunoresponse in the body. This will then make the host immune to future infections. Has been very successful in wiping out a number of once fatal and pandemic diseases (smallpox, polio, rubella, measles, etc.)
Unfortunately, the anti-vaccination (anti-vaxxer) pseudoscience movement has become powerful in the U.S. and other countries. It is true that, as with all medical treatments (or foods, or sports, or whatever) there have been some bad (even fatal) side effects. However, most of the anti-vaxxer movement has been promoted by falsified claims that purport to link vaccinations with illness such as SIDS, autism, etc. As a result, there have been some pockets of ressurgence of once-controlled diseases in populations where vaccinations have been reduced.
Public Health: even more than just vaccinations, improvements in the general public health are the main means to reduce disease in any population. This works on the principle that "an ounce of prevention is better than a pound of cure". Thus, such things as clean drinking water; sanitary disposal of sewage, waste water, and other waste; healthy diets; access to preventive medicine and first aid; and (when necessary) access to more extreme medical care (hospitalization, onsite treatment of infectious illness, etc.) can greatly reduce the spread of disease.