How Humanity is Changing the Course of Evolution Part 2: New Biomes, New Species

Part 1

Humanity is, without a doubt, the most extreme stimulus currently altering the course of evolution on Earth. Some of the changes are more extreme than others. One of the most extreme ways? The changes we've inflicted upon the planet have resulted in entirely new species. Now, to be clear, we're not just discussing deliberately bred human species here. While dogs, corn, and plenty of other species were deliberately bred by humans, and while these species have completely altered the shape of the planet, other species have been created by human action- more specifically, they've evolved in response to our construction of brand new, unique biomes. The first one we're going to talk about? A brand new species of mosquito.

The London Underground Mosquito, Culex pipiens molestus, evolved entirely in response to humans. [Image source]

The London Underground Mosquito is named for the location it evolved in- the extensive London subway system. Culex pipiens molestus evolved from Culex pipiens, a common English species of mosquito that traditionally only feeds on birds. At some point in the last century and a half of operation (the London Underground opened in 1863), mosquitoes that were trapped in the tunnels after construction began diverging into their own species, thanks to the unique biome of the London Underground. Amusingly, this process began

The London Underground is warm, cramped, and full of humans. This wouldn't have done the visually identical Culex pipiens any good- they only eat birds, hibernate during the winter, and have elaborate mating rituals that require lots of airspace. Thanks to the fast generations of mosquitoes, Culex pipiens evolved to feed on humans, stop hibernating, and adapt their mating rituals to the smaller spaces. In fact, their evolution has progressed to the point where Culex pipiens molestus can no longer easily breed with Culex pipiens- they're too genetically different, and it's all thanks to the creation of a remarkably new biome.

The London Underground. [Image source]

Unfortunately for humans, the London Underground mosquito has begun to spread worldwide. It thrives in similar warm, enclosed, and underground environments around the world. It's common in caves and sewers in Western Europe, and has been found as far away as New York and Tokyo, making it an extremely cosmopolitan species. Quite interestingly, while everywhere else the species only bites humans, Culex pipiens molestus bites both humans and birds in New York City- indicating that it's a further subspecies, likely an unlikely yet successful crossbreeding with Culex pipiens. One unfortunate consequence of this is that they were the primary vectors for West Nile Virus in the 1999 New York outbreak. Blood sucking insects that bite multiple species are excellent vectors for zootic diseases, like West Nile or bubonic plague.

That being said, humans have been creating new species since well before civilization- both deliberately and accidentally. The most obvious deliberate example is the dog, of course. One of the more interesting (and unfortunate) accidental speciations? Body lice. Body lice feed exclusively on humans, and, in fact, have evolved to exclusively lay their eggs in clothes. Interestingly, this allows us to guess at the time when humans first started wearing clothing- around 100,000 years ago, when the body louse split away from the head louse. In this case, the human body and its accompanying clothing is the new biome created.

Body lice are another species that have evolved around humans. [Image source]

We could go into much, much greater detail about the various parasites that have evolved around humans, but we're not? Why? Well, it's just really gross. Needless to say, when you have a species as absurdly successful as ours, that has reached the absurd biomass for mammals our size that we have, a lot of species are going to start trying to feed off us. Of course, it's not just human parasites that have evolved from humans- they've also evolved in plenty to feed off of our domesticated species. Cow specific parasites are the most notable, as the species that makes up the biggest chunk of our domesticated biomass. As we've brought cows into various novel environments in the species, they've basically become new biomes themselves for various parasitic species- hence the huge numbers of cow specific diseases and parasites out there.

Cattle, humanity's most significant domesticated animal by biomass (there are close to a billion and a half cattle on the planet), have provided an opportunity for the evolution of numerous species of parasites just for them. Lucky cattle. [Image source]

It's not just cows, however- our crops provide ample room for new species to evolve. One notable example is the fungus Fusarium oxysporum f.sp. cubense, better known as Panama disease, which specifically targets bananas. This seems like something of a silly threat until we note that bananas are the single most widely consumed fruit worldwide, and millions of people worldwide depend on it as a staple crop. The Cavendish banana, the main cultivar of banana eaten worldwide, is unlikely to remain a viable crop for longer than a couple more decades at most thanks the the fast spreading fungus- the same fate that wiped out the Big Mike (Gros Michel) banana, the previously most popular breed. It's so lethal because bananas- and many other domesticated species, especially crops- tend to be extremely genetically homogenous. Genetic homogeneity can drastically increase disease vulnerability in a species.

Whenever a new biome opens up, life WILL radiate out into it, adapting to whatever circumstances are available in it. In the case of the London Underground Mosquitos, humans were among the only reliable food sources available, so the mosquitoes evolved to feed on them. Mosquitoes in the London Underground construction sites being trapped underground certainly accelerated the process, at least, but it would have happened sooner or later. They've already likely had several hundred generations to evolve, which tells you how quickly evolution can occur. Human civilization has been around for around 500 generations, which gives you an approximate metric for human caused change for many species.

The stickleback is capable of speciating in astonishingly fast periods of time. [Image source]

Speciation can, of course, happen even faster than a few hundred generations- the marine stickleback, a ocean fish found all over the world, is notorious for colonizing freshwater rivers and lakes, each time evolving into a new species, with speciation occurring in 50 generations or less. (Some scientists think it might occur in 10). New species of finches have arisen in the Galapagos since Darwin visited. Evolution often happens very, very quickly- and, now that we're watching for it, is occurring right before our very eyes. And we're not dispassionate observers, either- we're driving it.

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Bibliography:

• http://www.bbc.co.uk/earth/story/20160323-the-unique-mosquito-that-lives-in-the-london-underground
• https://theconversation.com/humans-now-drive-evolution-on-earth-both-creating-and-destroying-species-61892
• https://www.nature.com/news/stickleback-genomes-reveal-path-of-evolution-1.10392
• https://en.wikipedia.org/wiki/Body_louse
• https://en.wikipedia.org/wiki/London_Underground_mosquito
• https://en.wikipedia.org/wiki/Cattle
• https://en.wikipedia.org/wiki/Banana
• https://en.wikipedia.org/wiki/Fusarium_oxysporum_f.sp._cubense
• https://en.wikipedia.org/wiki/Gros_Michel_banana
• https://en.wikipedia.org/wiki/Stickleback
• https://en.wikipedia.org/wiki/Three-spined_stickleback