The Viral Storm (5 page)

Now imagine that embedded within the stanza was a second poem so that both readings, the one that starts with the first letter and the one that starts with the second letter, lead to fluent comprehensible verses. Now imagine that you took the same stanza and read it backward and that a third hidden stanza emerged from the same letters. This is precisely what viruses can do. A good challenge to poets (or perhaps computer scientists) would be to create such a stanza to see if they could be as creative as natural selection has been with viruses. Viruses with overlapping reading frames use the same string of base pairs to code up to three different proteins, an incredible genomic efficiency, which makes their small genomes pack a much larger punch.

Overlapping reading frames represent just one of a range of adaptations that viruses have to negotiate their worlds. Perhaps even more important for viruses is their capacity to generate genetic novelty. Viruses have a diverse toolbox for altering themselves. Among the most fundamental is simple mutation. No organisms have perfect fidelity. Any time a cell in our body or a bacterium divides to create daughter cells or a virus replicates in a host cell, errors creep in. This means that even in the absence of sexual mixing, offspring are never the same as their parents. Yet viruses have taken mutation to a completely new level.

Viruses have some of the highest mutation rates of any known organisms. Some groups of viruses, such as RNA viruses, have such high error rates that they approach a threshold where any higher level of mutation would make them effectively crash due to the loss of essential function from the resulting errors. While many of the mutations harm the new viruses, the high number of offspring that viruses produce increases the chances that some mutants survive and occasionally outperform their parents. This raises the chances that they will successfully evade the immune systems of their host, get the upper hand against a new drug, or gain the capacity to jump to a completely new host species.

Middle-school biology teaches us that life is made up of sexual or asexual organisms. Yet viruses and other microbes exchange genetic information in ways that should make us question our early textbooks. When two different varieties of virus infect the same host, from time to time they infect the same cell, setting the stage for such exchange. In these cases, viruses sometimes create mosaic daughter viruses, which include some genetic parts from one of the viruses and completely different elements from another. In the case of reassortment, entire gene segments are swapped between certain kinds of viruses. In recombination, genetic material from one virus is swapped into a second virus. Genetic mixing of both sorts provides viruses with a rapid and radical way to create novelty. As with mutation, the novel daughter viruses have new blueprints that occasionally help them survive and spread.

*   *   *

Our knowledge of microbes is still young. This vast unseen world is critical to our planet and our species, yet we understand very little about it. We’ve already discovered most of the plant and animal life on our planet, but we regularly discover brand-new microbes. Ongoing studies of the diversity of microbes in animals, plants, soils, and aquatic systems represent the tip of a very large iceberg. The millions of specimens that will result from these studies will catalyze our understanding of life. Among other things, the knowledge will help spark the development of new antibiotics. It will also help us forecast the next pandemic. The microbial world is the “new world,” the last frontier of undiscovered life on our planet.

2

THE HUNTING APE

I wiped the sweat out of my eyes and swatted away the prickly branches in my path as I tried to listen for the screeches and hollers of the wild chimpanzees my colleagues and I had been trailing through Uganda’s Kibale Forest for the past five hours. The sudden silence of the three large male chimpanzees could only mean trouble. At times, such silence can foreshadow a sudden murderous rush into a neighboring territory to kill competing males. Or perhaps scientists. Chimpanzee warfare was not, thankfully, in the air that day. When our group emerged into a small clearing, we observed the chimpanzees seeming to quietly confer with one another as a crew of red colobus monkeys ate and played in the fig trees above, unaware of any danger. As two of the males inched up two nearby trees, the third—the apparent leader—created a diversion by screaming and scrambling up the tree toward the monkeys. Commotion ensued as the monkeys scrambled out of the tree and landed in the path of the other two hunters, waiting. One of the chimpanzees grabbed a young monkey and made his way to the ground to share his catch with his teammates.

As the chimpanzees feasted on the monkey’s raw flesh, a rush of thoughts ran through my brain: teamwork, strategy, flexibility. All in this close relative to humans. Truly, this was why people studied chimpanzees. While the rigors of scientific literature would never allow us to state this in technical journal articles, the reality seemed clear enough—these chimpanzees had worked collectively and strategically to mount a coordinated attack. The leader had diminished his chances of landing a kill by making a noisy attack, but the knowledge that his actions would increase the chances of success for his partners made this a strategic approach. In the end, they’d share the meat no matter who made the kill, exactly the sort of behavior that humans display every day. As the chimpanzees tore through the animal, it also occurred to me that the contact with the monkey’s blood and guts provided the ideal opportunity for our carnivorous kin to contract microbes.

*   *   *

Studying our closest living primate relatives affords us the opportunity to better understand ourselves, genetically, socially, and otherwise. However imperfect the conclusions we draw about ourselves from studying wild primates, we’re lucky to have them since the fossil record only offers its gems sporadically. Humans love the idea that we’re the chosen species—unique among the members of the animal kingdom—yet such claims should meet a high standard of proof. If our ape cousins share our supposedly unique traits, then perhaps they’re not unique traits after all. If, for example, we’d like to know if humans evolved the capacity to hunt or share food independently, we can look to chimpanzees and bonobos and ask if they exhibit the same behaviors. If they do, then Occam’s razor should push us toward concluding that we all share these traits because of shared descent: evolving the ability to hunt collectively twice or thrice within the very same close lineage is a less parsimonious explanation than simply concluding that hunting emerged in our joint ancestors before we split with them.
1
That a human trait is interesting does not mean it is unique to us. Many undoubtedly have ancient origins.

Some people have an almost instinctually negative response to the discovery that a treasured aspect of humanity is in fact not unique—that it’s actually something we share with other animals. Of course, the objective of science is not to uncover the things that make us comfortable but rather the things as they are. Another perspective on these shared traits is that they can help us feel less alone and more connected to the rest of life on our planet.

The parsimony rule of thumb applies not only to our behaviors. Each organ, each cell type, each infectious disease presents a new point of comparison with our kin. Are they found in us alone, or are they found in multiple other species along our same branch of the evolutionary tree? Through careful studies of humans and our closest living relatives we have the potential to at least begin to sort through historical mysteries and solidify which elements of humanity are unique and which are not. Already, earlier ideas that human traits like using tools or fighting wars were unique have been overturned by discoveries that chimpanzees engage in the same behaviors. What other supposedly unique human traits will fall next remains to be seen.

Fortunately, we have close living relatives that we can observe. The apes, our own branch of the primate lineage, include humans, chimpanzees, bonobos, as well as gorillas, orangutans, and the least studied apes, the gibbons. Studies of ape skeletons during the past hundred years provide a rough guide to the historical relationships among all of us. Over the last decade, a mass of genetic data from these animals has further refined the picture, providing a clear pattern of primate relationships. The information, commonly represented by the geneticists who study these data in phylogenetic trees such as the one below, helps to graphically describe how the relationships shake out.

The research reveals that for humans, two key species, chimpanzees and bonobos, lie closest to us. The other apes (gorillas, orangutans, and gibbons) differ substantially more and thus represent distant cousins of our human-chimpanzee-bonobo group. This relationship has led to the notion that humans are best seen as
the third chimpanzee
species, described in great detail in Jared Diamond’s book of the same title.

Once referred to as pygmy chimpanzees, scientists now recognize bonobos as an entirely separate species, yet one closely related to chimpanzees. Bonobos live only south of the Congo River in central Africa, while chimpanzees live only north of it. And while they look very similar, bonobos and chimpanzees have evolved to exhibit significant differences in their behavior and physiology during the time they’ve been separated by the great river. Current estimates suggest that the chimpanzees and bonobo lineages diverged roughly one to two million years ago. This divergence occurred some time after our own lineage separated from these cousins, around five to seven million years ago.

Phylogenetic tree, representing the evolution of apes.
(
Dusty Deyo
)

This research helps point us to a very pivotal and informative character in the evolution of our own species, a character referred to by anthropologists as the most recent common ancestor, which I’ll refer to simply as the
common ancestor
. Around eight million years ago in central Africa lived an ape species whose descendants would go on to include humans as well as the chimpanzees and bonobos.

We can use our parsimony rule of thumb and simple common sense to imagine the common ancestor in a bit more detail. It had extensive body hair and likely spent much of its time in the trees as do chimpanzees and bonobos. It lived in central Africa and consumed a diet dominated by fruit, tropical fruit in the fig family probably making up the major staple. Had we been able to study this ape, it would certainly have told us important things about what would come for us in the future, what changes were brewing. One thing that would end up affecting the future of our relationship with infectious diseases was a new tendency present in this animal: the urge
and
ability to hunt and eat meat.

An artist’s conception of “Ardi,” a female
Ardipithecus ramidus
, 4.4 million years old, representative of the most recent common ancestor between humans and chimpanzees.
(
Science Magazine / Jay Matternes
)

*   *   *

That humans share with chimpanzees the trait of hunting animals has been known for some time. It first emerged in the early 1960s when the British primatologist Jane Goodall documented wild chimpanzees hunting and eating meat at Gombe National Park in Tanzania during her pioneering efforts to study wild chimpanzee behavior. Before the Goodall studies and a related set of studies conducted by Japanese colleagues in the Mahale region of Tanzania, our understanding of chimpanzee behavior in the wild was largely nonexistent. The finding that chimpanzees hunted came as a shock to anthropologists, many of whom had come to believe that hunting had emerged after our split with chimpanzees and shaped our evolution in a way that distinguished us from them.

Since then, detailed studies in Gombe and Mahale as well as in some of the half-dozen more recently studied wild chimpanzee communities have solidified our understanding of the important role of meat in the chimpanzee diet. While chimpanzees hunt opportunistically, it is by no means sporadic. Chimpanzees can hunt forest antelopes and other apes (even humans), but they tend to specialize in a few critical species of monkey as prey. Their hunting is not only cooperative and strategic; it is also very effective.