The concept of human evolution rarely extends beyond discussion of the evolution of Homo Sapiens from Homo Erectus, and Erectus from the more primitive Australopithecus. We think evolution, and we think fossil records. We think finches. When we think of humans, we think of this succession of ancient bipeds. Infrequently do discussions of evolution in non-scientific communities broach questions of current or future evolution within existing populations of humans. It seems to be a commonly held belief that humanity as a whole began ducking the pressures that drive evolution when phenomena like modern medicine came into the picture. When questions of modern evolution in our own species are suggested, they are often met with ethical barriers. But what about human influence on evolution of other species?
As Professor David Tilman pointed out to myself and other students recently, Stanford scientist Steven Palumbi wasn’t afraid to think of evolution from an alternative perspective. He made a pretty compelling case for the notion that humans are the world’s greatest evolutionary force in a 2013 Science paper. The research produced some remarkable findings and as good science often does, put phenomena we observe often in our daily lives into a whole new context by examining them through an analytical lens. Palumbi asked: ‘what processes have we influenced or introduced into the biosphere that have had major impacts on ecosystem functioning? Of these, which have resulted in accelerated evolutionary changes through natural selection exerted by human technology?’ It is a powerful analysis that should remind us how far-reaching the influence of the technosphere has become. It should remind us that while our own species may not be identifiably* sensitive to the conditions that drive evolution, the strains our activities place on other species surely contribute to accelerated evolution for some. And as it turns out, it appears that this ramped up evolutionary pace has major implications for us, and for the environment.
Recognizing human-induced hyper-evolution isn’t tough, actually. The examples highlighted in the Science paper stem primarily from aggressive attempts at subverting disease and pests. Arms races between hosts and diseases, or pests and victims, are natural and have been underway for billions of years. These relationships drive evolution of increasingly advanced defense mechanisms for victims and ever-better infection vectors for diseases. The same arms races can exist in predator-prey relationships. But when we came along and began actively engineering defense mechanisms for ourselves and for our crops, the race-pace picked up. While our ability to design a calculated defense gives us a one-up in the race, it means we’re constantly having to figure out how to evade ever-better enemies. In some pretty important cases, we’re losing steam. Here are some of the heavy-hitters identified by Palumbi:
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Pesticides and herbicides. Applied liberally in most industrial agricultural settings, pesticides and herbicides reduce pest presences. But, insects typically evolve resistance to pesticides within 10 years of pesticide introduction, while resistant weeds do the same in 10-25 years.
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Antibiotics. The pharmaceutical industry works aggressively to stay a step ahead of antibiotic-resistant bacterial strains. A large portion of Staph infections are penicillin-resistant, and require much more powerful drugs to overcome. More powerful drugs tend to persist for longer periods in nature after they are expelled, and can thus drive further bacterial resistance in distant ecosystems. It can take as little as months for signs of resistance to new drugs to begin appearing. With antibiotics used in excess in most industrial animal husbandry operations, antibiotic-resistant infections are commonplace and can put nearby people at risk.
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Anti-Viral drugs. Because retroviruses evolve even more rapidly than bacteria, the use of vaccines for protection can involve yearly drug re-formulations to thwart the ever-evolving micro-enemies. The evasion of medical solutions by HIV is a result of this race we’ve never managed to get a stronghold on.
Other examples exist, but these three arguably have recognizable impacts on our own lives. While they may seem like distant phenomena, the results of such speedy evolution can be incredibly costly on both our economy and the environment. For example, US farmers spend an estimated $12 billion on pesticides per year, with 10% of these expenditures going directly to resistant pest evasion. More aggressive application of both can be toxic for other species and can increase the likelihood of leaching to water systems. It costs pharmaceutical companies an average of $150 million to develop a new product, which happens frequently in the face of drug-resistance. Resistant pests and diseases can pose even greater threats to other vulnerable species in nature, as they haven’t had the ability to evolve their own defense mechanisms at comparable rates.
With a more crowded planet on the horizon, and an increasing dependence on monocultured food crops vulnerable to wipe-out from pest invasion, inadvertent breeding of resistant diseases and super-pests becomes more important to dodge. But, there is a lot that we can do to avoid such a fate. For one, just being aware that our activities actually drive the evolution of better adept enemies can be enough to get people to change their behavior. Failure to complete full antibiotic courses, for example, is one of the primary behaviors that fosters quick development of antibiotic-resistant bacterial strains. If those too lazy to pop the last few pills really understood the biology behind their infections, the truth that such laziness may truly make it more difficult to fight the battle next time may ring a little more clear. Perhaps they would then think twice about ending early. Precautionary excess-pesticide and herbicide use could be replaced by precision application of such products. In turn, the environmental impacts of dumping massive amounts of toxic chemicals onto fields could be lessened, and less money could then be spent on (1) purchasing excess quantities of chemicals and (2) R&D to explore alternatives for pest/herbicide resistant cases.
If nothing else, perhaps it is valuable just to realize that the cogs of biology are still at work despite our attempts to groom the planet for our existence. We can’t eradicate disease and say goodbye to crop-jeopardizing bugs, because attempts to do so create the very conditions that drive the evolution of our tiny foes.
*Identifiably is surely the key word here. The raw definitions of evolution involve the notion of changing frequencies of genetic traits within populations, which certainly occur all the time. But if ‘identifiable evolution’ describes a noticeable phenotypic trend propagating through a population over an observable period, it’s tough to consider such a phenomenon occurring in human populations considering that as humans ourselves, we can observe only a couple of human generations throughout our own lifespans. However, the short reproductive lifecycles of the microbes and small creatures described in some of the examples below is, of course, largely what makes them so adept at evolving ‘quickly’ within observable timeframes.
