In the evolutionary driver’s seat, Homo sapiens, aka the modern human aka us, have done a poor job of keeping the wheel under control. Cataclysmic events and unrestrained endeavours have caused us to steer off track with abandon: climate change, habitat destruction and overconsumption, are just some of the many factors that have accelerated our wild trailblazing through Earth’s rich and varied species, leaving an unprecedented number of them in the past.
The extinction of species is a naturally occurring process – one which scientists worked out to occur at a rate of one to five species per year. However, unaccounted human behaviour means the previously assumed “background” rate of extinction is hugely inaccurate. Shifts in the way we live mean that we now lose closer to 100 to 1,000 species per million, per year.
The numbers make for a bleak outlook to anyone peering into the future of global ecosystem populations and the livelihood of organisms that inhabit them. Scientists constantly warn that we are headed towards the planet’s sixth mass extinction – an event likened to the destruction of the dinosaurs. But a little known side-effect of human activity is the evolution and spread of new species.
During World War II, masses of people would hide in the tunnels of the underground to seek refuge from the airstrikes which blitzed London. Co-habiting the place of shelter were mosquitoes – an uncommon sight in an environment dissimilar to the places where they were usually found. The mosquitoes found a way of persisting, breeding in standing water and feeding on humans rather than their usual prey of birds. The tunnels, dark, concrete, sheltered humans from the attacks and separated the below-the-surface mosquitoes from their surface counterparts. What resulted was the eventual adaptation of the mosquitoes to the underground; they formed a subterranean population which could no longer breed with their above-surface relatives. A new species was born.
It’s an example of just one of many species which have emerged as a direct consequence of human presence and activity, as indicated by a new body of research.
The Centre for Macroecology, Evolution and Climate at the University of Copenhagen collaborated with the University of Queensland, to lead a study published earlier this week in the journal Proceedings of the Royal Society B, demonstrating how and why human-made speciation has taken place.
The lead author Joseph Bull said: “The prospect of ‘artificially’ gaining novel species through human activities is unlikely to elicit the feeling that it can offset losses of ‘natural’ species. Indeed, many people might find the prospect of an artificially biodiverse world just as daunting as an artificially impoverished one.”
According to the study, human involvement doesn’t cause newly evolved species to replace extinct wild species, but does incite changes in places which otherwise wouldn’t see the introduction of a new species (not necessarily for the benefit of the different place).
A warning then, that extinction can’t simply be countered by human-made speciation. The study explores a number of factors which have driven this phenomenon – some inevitable, some terrifying.
For millennia, humans have travelled the world over and settled in the most far-flung locations. Relocation and movement of people to foreign lands has meant species have been transported along with them to new ecosystems in the process.
Though relocation can threaten the biodiversity of an area, it can also act as a mechanism of speciation. The study highlights that some relocated species can “undergo rapid evolution”, allowing them to establish their own genetic identities – distinguishing themselves as separate, individual populations as a result. Citing previous research as an example, the authors found that “70 per cent of introduced plant species studied changed at least one morphological trait (e.g. plant height), during a 150-year period in Australia.”
It’s not just relocation, either. Domestication and hunting have played pivotal roles too. Over the past 11,000 years, humans have domesticated 474 different animal species and 269 plant species globally, resulting in the “documented emergence of novel species.” Meanwhile hunting’s tendency to drive new trait development in animals – possibly as a result of adaptive, survival, and natural selection purposes – means that human-driven speciation is inevitable.
Domestication, relocation, hunting; these are all things which humans have done for thousands of years. But as new technologies shape our surroundings, there are no signs of a slow up in human-driven speciation. Future tools could bring back extinct species, while developments in genetics with the DNA-editing tool CRISPR and the continued cultivation of genetically-modified organisms (which aren’t themselves new species), could lead to “new self-sustaining lineages.”
For practical reasons, it’s difficult to accurately chart rates of speciation, just as it is to accurately measure rates of extinction. Nonetheless, the report makes it clear that since the last Ice Age, “255 mammals and 523 bird species have gone extinct, largely as a result of human activity”. It’s the same activity which has pushed Earth into the Anthropocene – an era categorised as a result of human-driven change; without careful reconsideration of our actions, that change could affect the diversity and range of species on the planet for the worse.