The German cockroach lives in buildings, cheek and jowl with us, outside it dies. African in origin it probably inhabited caves as many cockroach species do. It spread successfully around the globe following ancient man everywhere he went, being a pest and causing a nuisance. In the early 1990's, cockroach baits, attractive sugar treats laced with pesticides, were becoming increasingly ineffective. A pesticide scientist called Silverman needed to find out why. In 1993 he published a paper concluding that the German cockroaches aversion to glucose was the result of very rapid evolution. He reported that evolution has rewired the brains of sugar-hating roaches. That receptor neurons normally tuned to bitter tastes have become activated by glucose, so that the cockroaches perceive sugar as nasty rather than nice. Under ferocious selection pressure this has happened in a matter of years - perhaps as few as two.
Apart from the odd cockroach, our homes contain tens of thousands of bacterial species, hundreds of fungi and dozens of anthropods and worms. Some organisms have been evolving and living with us for 8 million years; some like the German cockroach are changing rapidly right now. Many of the microbes on, in and around us originate here. So do lice, be they head, body or pubic and probably also the mites that live in our eyelashes and the dust mites that float around us in the ether of dead skin covering us! As man began to settle from his nomadic origins, so the number of species living with us increased.
As our ancestors started returning to the same cave to sleep, new species evolved to take advantage. Bedbugs are close kin to bats and appear to have moved off bats and onto humans in a cave somewhere in eastern Europe or Asia, at some point in the past 100,000 years. As they did, they evolved. Their mouthparts became longer to pierce our thicker skin, they became nocturnal to avoid being detected, and their legs elongated to make it easier to get from one sleeping spot to the next. German cockroaches may have moved in with us at this point too.
The next big leap for biodiversity came with farming which began about 10,000 years ago in the east Mediterranean, a smorgasbord for our insect friends with stored products all around us. Many more species moved in and as they did, they evolved traits that made living alongside us easier. Forensic archaeology of property dated around 1300BC has found dermestid beetles, spider beetles, houseflies, bedbugs and dozens of other species preserved in the layers of accumulated sand; some had already evolved relative to their wild ancestors. Grain beetles for example, had lost their wings - a costly appendage, unnecessary when you can simply ride from place to place in transported grain. House sparrows are African, at some point near the dawn of agriculture they lost their habit of migrating every spring and autumn, evolved a new beak shape and moved permanently into human settlements. Similar stories emerge for house mice and brown rats both of whom have been with us for tens of thousands of years. It will be fascinating to speculate how future evolution of our lodgers will proceed. Today indoor spaces cover about 0.5% of the ice free surface area of the earth. By some measures the extent of the indoor space available to further colonise will have doubled by 2100. The larger the area of biome, the more species there will be that will evolve to live in it.
We are the primary agent affecting this evolution. Our homes are typically filled with the chemicals we use to kill other species - rat and mouse rodenticides, cockroach baits, ant baits, flea powder, antimicrobials, antibiotics and herbicides for our gardens. Depending on when, where and how often we use these chemicals, we are selectively killing those organisms least able to survive them and favouring the surviving genes and lineages of those able to resist them. We are creating new forms and they are rarely beneficial. A cockroach that is not attracted to sugar is bad news as is a bedbug that is resistant to insecticides. If we continue to try to eradicate organisms from our homes in this way, we will end up with even more species adapted to cope with our chemical warfare.
One solution may be to create genetically engineered species to live with us. That way we could replace harmful organisms with benign ones, or even create room mates that would help out around the house, perhaps eating bedbugs and fleas or cleaning mould from the wet room. One thing is for sure. The species that escape our chemicals will become ever more resistant to our attempts to evict them, lurking in the crevices, scurrying whenever we turn the lights on and leaving sugar pellets laced with poison uneaten. To remove all current known and evolving pests contact Pest Purge for permanent eradication. (Pubic lice excluded, sorry!)