Evolution has been going on since the first forms of life appeared on the planet billions of years ago. We have observed the creation and extinction of several species in the past through fossil records and we’ve seen it even in our lifetime. With evolution, you’ve probably known that it’s an incredibly long process occurring over geological times, spanning thousands and millions of years. As time goes on and the habitat changes, new species are created (speciation) or changes occur within the same species (anagenesis). But researchers have been observing a different phenomenon where species are rapidly evolving under pressure posed by several factors including climate change, commercialisation, pollution, etc. But before we try to understand this new phenomenon, let’s first explore what evolution is.
Evolution takes a long time
Although it’s insanely difficult to actually measure the average time required for evolution, a study from Oregon State University suggests that it takes a minimum of one million years. This holds true for long-lasting changes only and not the constantly occurring tiny changes. The reason behind this is because some of those little changes don’t necessarily last long. Mechanisms such as mutation, migration, natural and artificial selection, are collectively responsible for evolution. Several traits are developed gradually and the ones that stand the test of time, at least one million years later based on the study, will result in evolution that sticks around. Another thing to note is that even though species might undergo tiny changes in physical traits, there are chances that those traits might not make it to the next generation. For example, if a frog speciates to develop longer legs but doesn’t reproduce or gets eaten by a predator, the newly evolved genes responsible for the change won’t be passed along to the next generation.
Sometimes, minor genetic changes might range between a few years to something as short as just a few hours. This is dependent on the life cycle of the species. Organisms with high reproductive rates result in the creation of numerous generations in the span of a few days and months. This is observed in microorganisms and considering their size, it’s justified. However, it’s being observed that bigger organisms such as lizards, rodents, fish, etc., are evolving quicker than expected, in the span of a few decades. Scientists call it “rapid evolution” and more research is being conducted. While earlier it was accepted that it wasn’t possible to observe natural evolution in our lifetime, studies of fossil records and experiments that have been carried out to determine the effects of certain factors to evolution are giving us a lot of new information.
Rapid evolution isn’t new
Last year, fossil hunters in China discovered the skeleton of a toothless marine reptile, that might have lurked the Earth 247 million years ago. Ichthyosaurs are closely related to marine reptiles and they usually have a long snout, teeth and a tail, including fins. Surprisingly, the newly discovered fossil didn’t match those features and was in fact toothless with a short snout and long tail. Based on its strong body and small skull, it was named Sclerocormus parviceps. The creature was alive when the Earth had just experienced the “Great Dying” event, or the End-Permian mass extinction, around 252 million years ago. Fresh from the catastrophe and after a few million years, many creatures were believed to have been claiming their dominance over the planet. Back in 2014, the fossil of apparently the first amphibian was discovered, named Cartorhynchus lenticarpus, which displayed similarities to Sclerocormus but also was smaller in size and had a shorter tail. The fossil is said to be around 250 million years old, suggesting that creatures were drastically evolving. This was mainly because of the huge void left after the mass extinction that killed off nearly 96% of the species on the earth. In the span of a few million years, a diverse pool of creatures were already present in the waters and on land, pointing towards rapid evolution on a global scale in the Triassic period.
Although this was the oldest and probably the first known event of rapid evolution yet, it’s known that mass extinction encourages it. The Cretaceous-Paleogene extinction event wiped off all the dinosaurs from the face of the earth. Yet another void was left in the ecosystem that had to be filled in by other species, mostly land creatures. Among the creatures that profited from the death of dinosaurs were frogs, according to a study. Most of the dinosaur population were herbivores and in their absence the vegetation flourished. This allowed frogs to take over the forests and become arboreal (start living in trees). There was abundant food for the frogs and the threat from predators was solved by another shift in their reproductive cycle. Some frogs were able to skip the tadpole phase and directly grow into adult frogs. As a result, approximately 88% of the current frog species originated in this period.
This might not be a surprise to many but even humans have been evolving rapidly, especially in the last 40,000 years. Considering this pace, if we were to evolve the same way when humans and chimpanzees first diverged (dating back to 6 million years ago), the genetic differences would have been 160 times greater. This evolution was also motivated by the discovery of agriculture some 10,000 years ago. The main driving factors for this rapid evolution in humans include environmental changes and the population explosion which multiplied the number of mutations generated.
The above-mentioned events describe evolution over several generations and even millions of years. Although it’s a really long period, these particular events highlight those instances where the evolution was quicker than conventional time periods. These events have been determined through fossil records but in recent times, rapid evolution is being observed in our lifetime in a shorter time scale of a few decades and few generations.
Causes of rapid evolution
We are primarily to blame for most of the recent rapid evolution events across organisms. Several instances of forced adaptations have been motivated by our own actions. Be it encroachment of natural habitats or artificial selection of species, many of these have been caused by us. And with such hostility, the species have been forced to evolve in order to survive. But not all organisms have been successful in evolving to survive from the ongoing mass extinction. You read that right! The Holocene extinction or the sixth mass extinction has been underway for thousands of years now, ever since we started dominating the environment, and it gains momentum every year. Population explosion and the resources required to sustain this enormous population have pushed many plants and animals towards extinction.
There have been several instances where organisms have undergone rapid evolution directly because of human activities leading to environmental changes. The peppered moth is a popular example from during the industrial revolution. Air pollution caused by coal smoke covered and darkened the barks of the trees in England, resulting in light pepper moths standing out to predators. Dark-coloured peppered moths found themselves in a favourable position and were able to survive and proliferate. This is pure natural selection at play. The numbers of light peppered moths dwindled as birds were able to easily spot them. Eventually, when the air became cleaner, the barks went to their natural colour. This switched the advantage back to the struggling population of the light moths, and now dark-coloured moths were being easily spotted by predators.
Climate has always played an important role in the evolution of species. With the changing landmass and human encroachment, animals and plants have been forced to move into different areas with different climates. The only way to survive is to adapt to the local climate. You would naturally think that such an adaptation would take millions of years of evolution but a recent study suggests that it can be possible in just a single winter storm. A certain species of green Anole lizards in the southern part of US evolved resistance to cold weather after a record-breaking cold storm in 2014. Originally, the team of researchers from the University of Illinois was trying to study the capability of the cold-blooded reptiles to survive in the cold north. After the extreme storm hit the region, they went back to the region to collect data from the reptiles. They found that the lizards had developed 14 genomic regions, enabling them to build resistance to the new cold climate. According to them, this was confirmed by DNA markers, gene expression levels, and physiology measures.
Most of the reported instances of rapid evolution have been linked to human intervention either through natural habitat encroachment or climate change (pollution to be precise). Pollution is already considered a big factor forcing rapid evolution and another instance was observed in the State of New Jersey, US. The Atlantic killifish thriving in the Lower Passaic River were burdened with toxic leftovers including DDT. Surprisingly, few pockets of the killfish population were able to adapt to the toxic waters and managed to survive. A specific water flea called Daphnia was found to have an increased thermal tolerance in just a duration of two years, owing to increasing temperatures thanks to global warming. To understand rapid evolution better, biologists wanted to study their causes better and try to repeat them.
Studying rapid evolution
The best way to study rapid evolution is to observe it in a natural habitat rather than depend only on controlled lab experiments. We already talked about how microorganisms or smaller organisms are favourable to study because of their shorter lifespans and rapid reproductive cycle. Hence, it is much easier to study or observe mutations or any evolutionary changes in them. Biologists have also ventured into isolated regions or islands to introduce an external factor or species to influence evolution in that area. They weren’t certain whether they would observe dramatic evolutionary changes or even finish the study in their lifetime. But they were in for a surprise.
A lab study by the University of Leeds found that the age of adulthood of soil mites doubled in just 15 generations and there was also a significant change in population sizes. Soil mites were taken from the wild and transferred into 18 glass tubes. While they reproduced in the controlled environment, forty percent of adult mites were removed every week from six of the tubes. Similarly, juveniles mites were removed from six other tubes. The remaining six tubes were left untouched. The consequence of these conditions led to a slow growth in juveniles in all but the six untouched tubes. And when they finally matured to reproduce, they were larger compared to previous generations. This further made it easy for them to lay eggs, highly influencing population sizes.
Forcing species into new habitats can either completely shuffle the ecosystem or they might simply die out. An island experiment with Italian wall lizards was conducted in 1971, where they were moved to a neighbouring island in the south Adriatic Sea. Wall lizards from Pod Kopiste were introduced to a neighbouring tiny island called Pod Mrcaru, and after a few decades, scientists witnessed shocking results. It wasn’t until 2004 that the team of researchers went back to the island and found that the island was swarming with a new species of lizards. However, these lizards had evolved drastically, something which the researchers say would have taken millions of years. The lizards developed a completely new gut structure to accommodate a vegetarian diet which was originally built for an insect-based diet. Their expanded gut was able to digest the vegetation’s cellulose turning them into fatty acids. They also developed a larger head to support stronger bites to munch on the plants. Equipped with a plant-based diet, the lizards didn’t have to depend on insects for food and could feed on plants abundantly present around them. Because of this, survival wasn’t much of a problem and the species flourished to grow in population.
Back in 1978, biologist David Reznick (then a graduate student) had set out on a journey to Trinidad to “watch evolution happen”. The test subjects were guppies, a species of tropical fish in the Caribbean islands with a high reproductive drive. Reznick wanted to experiment whether predators could affect the genetic adaptation of guppies in a controlled environment. He moved a batch of guppies from a location rich with cichlids, a species of fish who feed on them, to a stream without any predators. Alternately, predator-free locations with guppies were populated with cichlids. After going back to these sites, Reznick observed remarkable changes where the predator-rich areas had smaller-sized guppies who matured at younger ages. This was driven by the aggressive predators that made more production of babies a priority. Whereas, the predator-free areas saw larger guppies maturing at a later age and reproducing slowly. Their survival wasn’t at stake anymore, hence they evolved to take things slowly. And the most shocking observation was that these changes occurred in just a span of four years.
It’s clear that humans had a significant role to play in the recently observed instances of rapid evolution in nature. Of course, we can’t say for sure whether these changes are going to last in those species over the long run. Not just global warming or climate change, we have other activities such as hunting, harvesting, fishing, agriculture, urbanisation, and a number of other causes responsible of these changes. We have not only affected the global ecology of the planet, but as mentioned above, we are interfering with the evolutionary trajectories of several species. In a human-dominated environment, this is bound to happen and it’s unlikely that our interference with the natural order of things is going to reduce. The next best step forward is to understand the trajectory that we have induced on these species to predict how things are going to turn out in the future. We also need to have enough data to be able to predict the economic and social costs of these changes, in order to prepare ourselves for the implied consequences. It would be an ironic example of karmic justice if our influence on the global ecology comes back to threaten our very existence on this planet.
This article was first published in the September 2017 issue of Digit magazine. To read Digit’s articles first, subscribe here or download the Digit app for Android and iOS. You could also buy Digit’s previous issues here.