From megafauna extinction to the London Underground mosquito: how human activity drives evolution

A tragically extinct bit of megafauna. Image: Hulton Archive/Getty.

When scientists examine the impact of humans on the planet, the focus is mainly on the extinction of species. But increasingly researchers are looking at the idea that humans, through animal domestication, relocation and hunting, have become an evolutionary driving force that has led to new species, new traits and novel ecosystems.

A new paper, recently published in the Proceedings of the Royal Society B, argues that if we are to preserve the biodiversity of life that we value, we need to understand both the nature of this human-driven creation – a process known as speciation – as well as the effects of human-driven extinctions.


A drive to extinction

Look at humans’ effects on Earth’s plant life. Over recent decades, the amount of new plant growth each year across the world appears to have been relatively constant. However, between 25 per cent and 38 per cent of this fresh plant growth is appropriated by humans – for food and other purposes – reducing the amount available for millions of other species.

Thomas Crowther and colleagues at Yale University estimated that before the industrial revolution there were 6bn trees on Earth. There are now only 3bn. This deforestation and the conversion of land to produce food, fuel, fibre and fodder, combined with targeted hunting and harvesting, has resulted in a rate of species extinction some 100 to 1,000 times higher than would have been expected without human intervention. This probably constitutes the beginning of the sixth mass extinction in Earth’s history – an enormous impact on the planet and one reason why many scientists have declared that we have entered the Anthopocene Epoch.

Species removal isn’t a random process: a disproportionate number of those driven to extinction are the larger animals, both on land and at sea. This “megafauna extinction” began 50,000 years ago: unbelievably, half of all large-bodied mammals worldwide, equivalent to 4 per cent of all mammal species, have been lost in that time. And extinctions are not just confined to mammals: since 1500CE there have been 784 documented extinctions, including 79 mammals, 129 birds, 21 reptiles, 34 amphibians, 81 fish, 359 invertebrates and 86 plants.

Domestication and relocation

Humans have also domesticated around 474 animals and 269 plants to meet their needs, and this has led to the emergence of new species. Of the world’s 40 most common agricultural crops, eight can be considered entirely new species, just as animal domestication has created new species of animals such as the dog and domestic pig.

Animal domestication has also led to a major shift in animal distribution. According to Vaclav Smil of the University of Manitoba, of the weight of all the planet’s land mammals, humans make up 30 per cent, domesticated animals make up 67 per cent, and wild mammals just 3 per cent. Organisms have also been transported around the world – including crops, domesticated animals, and pathogens such as viruses and bacteria. This movement has led to a small number of extraordinarily common species such as the brown rat, new hybrid species such as mules, and a general homogenisation of the animal and plant life found on Earth.

There’s more to animal domestication than you’d think. Image: XKCD/creative commons.

This biological relocation started in the 16th century when species from the Old World of Europe and Asia were exchanged with those in the New World (the Americas). This is known as the Colombian Exchange, which led to the globalisation of human food, with New World crops such as maize/corn, potatoes and manioc/cassava swapping places with Old World crops such as sugarcane and wheat. Domesticated animals swapped continents, too.

Many of these plants and animals have since undergone rapid evolution in their new environments, leading to the emergence of new species. Accidental transfers from Europe occurred, too: smallpox, measles and typhus killed over 50m people in South and Central America during the colonisation of the New World. These exchanges continue today, and invasive species have become a major concern on all continents. Mark van Kleunen and colleagues at the University of Konstanz suggest that 4 per cent of plant species have been relocated around the globe, equivalent to all the native plant species in Europe.

These changes are the first of their kind since the supercontinent Pangaea separated about 200m years ago, but in fact the extent of the current epoch’s trans-oceanic exchanges are unprecedented.

Something borrowed, something new

Most ecosystems have been altered by humans, to the extent that the concept of a “natural” biome, completely free from human influence, is obsolete. This has led Erle Ellis at the University of Maryland to suggest that we consider them Anthromes – those ecosystems where most of characteristics have been reshaped by human activity. While many have undergone significant loss of biodiversity, through change they also create environments that allow opportunities for the emergence of new species.

Culex pipiens f. molestus, the mosquito species unique to the London Underground. Image: Walkabout12/creative commons.

An interesting example is that of the common house mosquito (Culex pipiens) which has become adapted to London’s underground railway and established a subterranean population of mosquitoes distinct from any other on Earth. Now called the London Underground mosquito, it has diverged sufficiently from its cousins above ground that it can no longer interbreed with them and exhibits significantly different behaviour.

So through breeding, harvesting and transport of crops and animals, and the impact of higher air and surface temperatures that result from greenhouse gas emissions, humans have, and continue to, alter the evolutionary process of the other species sharing this planet with us.

If we consider also the scientific development of diverse new biological products such as antibiotics, pesticides and novel genetically engineered organisms, humans have indeed become the world’s greatest evolutionary force capable of shaping our world by creating new species and destroying others.

If we are to help preserve the millions of species on Earth, we must consider the impact of humans in terms of these creative and destructive forces.The Conversation

Mark Maslin is professor of Climatology at UCL.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The Tory manifesto promises to both increase AND decrease the rate of housebuilding

Housing secretary Robert Jenrick. Image: Getty.

In his 2014 Mansion House speech, the then-chancellor George Osborne expressed with uncharacteristic honesty the motives at the heart of how the Conservatives see British housing politics: “The British people want our homes to go up in value, but also remain affordable; and we want more homes built, just not next to us.”

Five years later these contradictions remain unreconciled and present in their manifesto, which contains two different and contradictory – but clearly extensively targeted and focus-grouped – sets of policies.

The Conservatives have two housing targets. The first is to make significant progress to hitting “our target of 300,000 houses built a year by the mid-2020s”. The second is their aim to build “at least a million new homes” during the next parliament, which implies a target of 200,000 homes a year. This is not only 100,000 lower than their initial target but also lower than the current rate of housebuilding: 213,660 new homes a year. They have therefore implied at separate points in the same manifesto that they intend to simultaneously increase and decrease the rate of housebuilding.  

There are similar conflicts in their approach to planning. They intend to make the “planning system simpler” while simultaneously aiming to introduce community-led design standards for development and planning obligations to provide infrastructure for the local community.

None of this is unsurprising, The Tories don’t seem to know if they want to build more houses or not – so of course they don’t know whether they wish to make it easier or harder to do so.  

Politicians like obfuscation on housing policy to placate NIMBY voters. Take for example prospective Conservative MP and ‘environmentalist’ Zac Goldsmith’s crusade to save treasured local car parks. The manifesto can equally be accused of pandering to NIMBY instincts, protecting their shire voters from all housing, including ones they might actually need or want, by promising to protect the greenbelt.  

Instead, Conservatives intend to foist development on Labour-leaning inner-city communities and prioritising brownfield development and “urban regeneration”. This requires massive, infeasible increases in proposed density on brownfield sites – and research by Shelter has shown there are simply not enough brownfield sites in cities like London. Consequently, it is not clear how such a policy can co-exist with giving these inner-city communities rights on local design. Perhaps they intend to square that circle through wholesale adoption of YIMBY proposals to let residents on each street opt to pick a design code and the right to turn their two-storey semi-detached suburban houses into a more walkable, prettier street of five-storey terraces or mansion blocks. If so, they have not spelt that out. 

Many complain of NIMBYism at a local level and its toxic effects on housing affordability. But NIMBYism at the national level – central government desire to restrict housebuilding to make house prices rise – is the unspoken elephant in the room. After all, 63 per cent of UK voters are homeowners and price rises caused by a housing shortage are hardly unpopular with them. 


There is anecdotal evidence that protecting or inflating the value of homeowners’ assets is central to Conservative strategy. When George Osborne was criticised for the inflation his help to buy policy caused within the housing market, he allegedly told the Cabinet: “Hopefully we will get a little housing boom, and everyone will be happy as property values go up”. More recently Luke Barratt of Inside Housing noted that most Conservatives he spoke to at the 2018 party conference were scared “they’d be punished by their traditional voters if the values of their homes were to fall”. He was told by a Conservative activist at the conference that, “If you build too many houses, you get a Labour government”.

But the senior figures in the Conservative Party are painfully aware that the continuing housing shortage presents major long-term problems for the Party. As the manifesto itself acknowledges: “For the UK to unleash its potential, young people need the security of knowing that homeownership is within their reach.” Perpetual increases in house prices are incompatible with this goal. The problem has greatly contributed to the Conservatives’ severe unpopularity with a younger generation priced out of decent accommodation. 

Equally, there is increasing evidence that ‘gains’ from rising house prices are disproportionately concentrated in the south of England.  The differences in housing costs between regions greatly reduce labour mobility, suppressing wage growth in the north and midlands, which in turn leads to greater regional inequality. The policy of coddling southern homeowners at the expense of the economic well-being of other regions is a major long-term stumbling block to Conservative desires to make inroads into the ‘red wall’ of Leave-voting labour seats outside the south.

Before dealing with the issue of where housing should go, you must decide whether you want to build enough housing to reduce the housing crisis. On this issue, the Conservative response is, “Perhaps”. In contrast, even though they may not know where to put the necessary housing, the Labour Party at least has a desire in the abstract to deal with the crisis, even if the will to fix it, in reality, remains to be seen. 

Ultimately the Conservative Party seems to want to pay lip service to the housing crisis without stopping the ever-upward march of prices, underpinned by a needless shortage. Osborne’s dilemma – that the will of much of his party’s voter base clashes with the need to provide adequate housing – remains at the heart of Conservative housing policy. The Conservatives continue to hesitate, which is of little comfort to those who suffer because of a needless and immoral housing shortage.

Sam Watling is the director of Brighton Yimby, a group which aims to solve Brighton’s housing crisis while maintaining the character of the Sussex countryside.