Right now, humanity is engaged in an epic battle against fast-adapting and merciless predators. No, zombies are not beating down doors to tear chunks of flesh out of the living. Rather, humanity is being hunted by deadly pathogenic bacteria that have gained resistance to antibiotics.

And thanks to the peculiar incentives that drive the pharmaceutical industry, it looks like the cavalry may be a long time in coming.

To understand the current state of the antibiotics market, we have to go back millennia. Humans have co-existed with bacteria throughout our history. They live in our bodies from birth to death. It’s estimated that up to three percent of a typical human's body mass is made up of symbiotic bacteria, which assist us with bodily functions like digesting food.

Most bacteria in the human body are kept in check by the body’s immune system. But bacteria are constantly evolving to survive and reproduce. Either the immune system successfully adapts to new threats, or the body risks being overrun. Sometimes the immune system will fail to respond to a novel bacterial threat, allowing the bacteria to kill the host.

Before antibiotics were widely available, any accident, injury, or medical procedure that allowed pathogenic bacteria into the body was potentially deadly. One in nine skin infections was fatal. One in three cases of pneumonia led to death. Invasive surgeries including caesarean sections left the patient open to killer infections. Insect bites, burns, and blood transfusions frequently became a source of infection.

So the discovery of the first antibiotic, penicillin, by Alexander Fleming in 1928 remains one of the high points in medical history. Antibiotics kill bacteria, which meant wounds were no longer death sentences. Yet when Fleming won the Nobel Prize for medicine in 1945, he warned of the dangers of antibiotic resistance:

It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them… There is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant. []

Fleming’s prediction was right. Penicillin-resistant bacteria arrived while the drug was still being given to only a few patients. Each new class of antibiotics since then has soon been greeted by resistant bacteria.

One breeding ground for antibiotic-resistant bacteria is in farm animals. Low doses of antibiotics have been used since the 1950s to enhance growth. In the U.S., over 80 percent of all antibiotics are now used on farm animals. But low doses encourage resistance, just as Fleming warned. Recent studies show that antibiotic-resistant bacteria have been found widely in farm animals raised for meat, as well as wild animals, including crows, foxes, and sharks.

Scientists are fighting a running evolutionary battle with the bugs. A patient in New Zealand died this year after contracting an infection resistant to all known antibiotics. Doctors declared him the first patient of the "post-antibiotic era." The Centers for Disease Control and Prevention recently warned that drug-resistant bacteria kill at least 23,000 people annually in the U.S, and cost the health care system $20 billion per year.

Unfortunately for the human race, research into antibiotics remains costly. One estimate suggests that the cost of bringing a new antibiotic to market is over $1 billion, and that new antibiotics lose $50 million on average. There are far more profitable drugs for pharmaceutical companies to throw money at, since antibiotics are usually single-serve drugs for humans, not long-term treatments.

Drugs for chronic conditions tend to be more profitable. And with drug resistance quickly evolving, rendering older antibiotics ineffective, pharmaceutical companies have even less incentive to invest in the drugs.

The economics are perverse. Taking preventative action today would not be very profitable because there are fewer potential customers. The incentives to produce more and better antibiotics only kick in under the worst circumstances, when millions of people are dying from antibiotic-resistant infections.

With investment, there would be plenty of reasons to be optimistic about the future. New antibiotics today are typically discovered by culturing bacteria in a laboratory, and scientists so far have cultured less than one percent of the bacterial species on the planet, meaning there is still a huge pool of possibilities out there that remains untested.

There are also a large variety of organic compounds — for example, from insects — that may hold promise as antibacterials. Some scientists are even looking into the possibility of using nanotechnology to fight bacteria — tiny machines that can hunt down pathogenic bacteria and destroy them. Sooner or later, one of these approaches may yield an innovation that pathogenic bacteria cannot develop resistance to.

In July 2012, President Obama signed the GAIN (Generating Antibiotic Incentives Now) Act, a bipartisan bill to fast-track the creation of new antibiotics. Twelve new antibiotics in development have so far received fast-track status, which should speed up the approval of new drugs for difficult-to-treat conditions.

But whether the law will be sufficient to create enough new antibiotics to win the evolutionary arms race remains to be seen. Developing antibiotics is still expensive, and the antibiotics that we do have are still being over-prescribed for humans and doled out in sub-clinical doses to farm animals — both of which gives bacteria opportunities to develop resistance.

If the problem continues to grow, the U.S. and other countries will have to invest a whole lot more in antimicrobial technologies, or create incentives for Big Pharma to do so. Like the zombie apocalypse, the post-antibiotic world would not be a pretty place to live in.