So much can happen in a million years. It took us only about 2.5 million years to evolve from the first member of the Homo genus to our current status as Homo sapiens. What changes does evolution have in store for the next million years? We consulted some evolutionary biologists for predictions, most of which concern the next several hundred years.
Before we get going, we should mention that scientists find it much easier to describe the events of the past million years than to predict the next million -- not just easier, but more accurate. Nevertheless, a few took the plunge, and we're passing on to you the predictions they could make with confidence.
Get ready to say yikes!
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No. 10 - Deadlier Malaria
In the past 10,000 years, most humans have changed their way of living. From nomads, we became agriculturists. We now inhabit one place year-round -- often densely -- and we provide habitat, like irrigation ditches, for insects to live. The insects that feed on us, like mosquitoes, now live with us. Over the past million years, we've domesticated them, says Stephen Rich, an evolutionary biologist who studies vector-borne diseases at the University of Massachusetts, Amherst.
Since mosquitoes are residing with us, the parasites found on those insects, like the Plasmodium species that cause malaria, are also living with us. Our close quarters with these parasites will guide their evolution over the next few centuries, says Rich. Because we've made it easy for the malarial parasite to find us and its mosquito hosts, nature isn't selecting for the 'finding host' genes as strongly anymore. Now, the pressure is on other traits the parasite needs to survive, like quickly reproducing inside of our cells, which will probably make the parasite deadlier, says Rich.
No. 9 - Pathogen Arms Race
Since the beginning of medicine, we've attacked the organisms that make us sick. We've swallowed antibiotics to fight bacteria. We've poisoned parasites. We've vaccinated and boosted our immune systems to quell infections. We've put a lot of pressure on the pathogens. The only ones that can survive are those that resist our treatment.
Resistant organisms often survive because they can breed and share genes quickly, faster than we can kill them. Even if we stamp out an infection in a single person, it is difficult to drive a particular pathogen extinct because often some survive in someone, somewhere in the world. There are many reasons for that: People can't afford the effective drugs, they take the wrong drugs or the wrong dose, or they don't take them for the right amount of time. Overall, our efforts to treat infectious disease are driving microbes toward resistance, which means we need new treatments. This arms race will continue as long as we try to suppress or kill organisms that invade us, says Stephen Rich.
No. 8 - Rock-Paper-Scissors
We're not talking about the children's game. But in a way, we are. It's an analogy for a pattern that's so reliable, it has governed lizard mating for hundreds of millions of years, and the scientists who discovered it say it will continue for at least the next million.
Here are the rules: "Ultra-dominant" males (the "rocks") are big and range widely to find females. "Sneaky" males (the "paper") look like females and steal other male'' mates. "Guarding" males (the "scissors") band together to defend territory. And, like the game says, rock beats scissors; paper beats rock and scissors beat paper. The winning lizard mates with the most females. Amazingly, the winning variant of lizard has cycled from rock, to paper, to scissors regularly. No one wins overall, which for lizards, means the survival of all three variants.
No. 7 - Evolutionary Pressure from Climate Change
According to the Intergovernmental Panel on Climate Change (IPCC), the average temperature on the surface of the Earth will warm about 0.2 degrees C each decade for the next 20 years. In about a century from now, the Earth's surface will be an average of 1.8 degrees C warmer than it was between 1980 and 1999, by the IPCC's most conservative estimate.
If that happens, organisms across the globe will have to respond to the warming, says Mark Urban, an evolutionary biologist at the University of Connecticut. They'll need to move, adapt to the new local climate or die, he says.
No. 6 - No Evolutionary Pressure from Climate Change
The IPCC's predictions are controversial. Some scientists look at the same climate data as the IPCC group did and conclude that the Earth is not significantly warming. For example, by running different statistical analysis on the same data, Willie Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics found that the 20th century was not significantly warmer than any other century in the last thousand years. Furthermore, they say the Earth may not warm in the next century and may even cool. For experiment's sake, the rest of our predictions will cover what might happen if the Earth warmed as the IPCC predicts.
No. 5 - Species Change Their Range
To take the example of North America, under the Intergovernmental Panel on Climate Change's (IPCC's) predictions, the climate we are used to seeing in the southern United States will pick up and move northward, as biologist Mark Urban describes it. North America's temperature gradient will shift northward. Some organisms will move with it. These emigrants will be organisms that haven't inhabited their current range for very long, thus limiting the time they've had to adapt to local conditions. They will also have bodies built for movement, like birds, wolves and, as we'll see next, insects.
No. 4 - Pests (and Diseases) Move North, Too
North America isn't the only continent that has a temperature shift in its forecast. The Intergovernmental Panel on Climate Change (IPCC) predicts that the entire Northern Hemisphere's temperature gradient -- cooler toward the North Pole and warmer towards the equator -- will move north. Ticks and mosquitoes will then shift their ranges north. Then, deer and other wildlife will acquire these pests, whereas these populations had been too far north to acquire them before, says Stephen Rich. And the diseases these insects carry will also move north.
For instance, the lone star tick carries a bacterium that causes a rash and fever in humans called ehrlichiosis. In the Unites States, concentrations of cases have moved from Virginia to Massachusetts, according to Rich, and he says this mirrors warming in the northern states. But whether it's erhlichiosis in Maine or malaria in England, the last word on whether we see more cases of the disease with warming will depend on the strength of local health care.
No. 3 - Species Adjust to Temperature Change
Not all organisms that feel the climate change around them will move. Some will make the best of their new situation and stay put, says Urban. These organisms won't be very mobile, like oak trees. They'll also be genetically diverse, with some individuals in the population adapted to slightly warmer than the local temperature, and some adapted to slightly cooler. Evolution will then have variation to work on. What will happen next is a shift in success. "If the area warms, warmer-adapted organisms that were struggling under cooler temperatures will survive better, have more kids and become favored," says Urban.
No 2 - Species Can't Survive Temperature Change
Falling into a third category, says Urban, are species that can't move to follow their preferred climate and are blocked from adapting, either by a local competitor that replaces them or because there's no variation for selection to work on. They'll be at risk to go locally extinct. Urban gives the example of species at the equator that are already adapted to the hottest temperatures on Earth. If this area warms, and no individuals are adapted to hotter than the hottest temperatures, the species will be at the mercy of processes that mix new variation into the population before most individuals die.
No. 1 - Mountain Lizards Decline
Speaking of extinction, a group of ecologists led by Barry Sinervo of the University of California, Santa Cruz, wanted to understand how climate change would affect lizards. They carried out a local study on lizards in Mexico and found 12 percent of the species went extinct between 1975 and 2009. They uncovered a pattern in the extinctions. As the cooler mountaintops warmed, mountain lizards went extinct, and lowland lizards expanded up the mountains, where it was now warm enough for them to live.
They repeated the study at sites around the world, seeing the same disappearance of cold-adapted lizards from mountaintops with replacement by lowland lizards, the overall result between 1975 and 2009 being 4 percent of the lizard populations at their sites going extinct. By projecting the temperature trends at their global sites and using data on the breeding temperatures and the global distribution of lizards, they predicted that 30 percent of their lizard populations would go extinct by 2080.