By Dr Valerie Jeffries.

Walking along briskly for my lockdown exercise I was watching the starlings congregate for their evening swarm on the TV aerials, and listening to quarrelling sparrows and the raucous yells of the seagulls way inland. Many birds have adapted to live alongside humans in our urban landscapes, some like the house sparrow now almost world-wide, having become established in Europe thousands of years ago from their original Asian steppe homeland. They build nests in crevices of our buildings and hunt insects in the guttering and appreciate the seeds (and flowers alas) in our gardens and grain in our fields and barns. When their numbers declined in Britain 20 years back people were urged to support them, though when more abundant they are often regarded as a nuisance, in contrast to rarer and more colourful small birds. These days it is green parakeets that are resented in the Home Counties, as unwelcome intruders, though they too are prettier than sparrows.

In parts of America sparrows are unwelcome by comparison with the native bluebirds. Introduced in the nineteenth century as a failed experiment in biological pest control, sparrows went on to multiply vigorously and compete successfully with the bluebirds, which are prettier and indigenous.

There is never a valid ‘primaeval’ time to determine what should be protected and what removed, as ecosystems are constantly evolving.

The notion of natives and unwelcome intruders depends a lot on the date picked for reference, which may be some long-gone era before Mankind even arrived, or a time preserved in myth, or linked to childhood memories. There is never a valid ‘primaeval’ time to determine what should be protected and what removed, as ecosystems are constantly evolving.

Since the quiet of social isolation has left our streets and parks to the wildlife, people are observing more animals who share our urban habitat, and realising that for some species human presence is a benefit, an opportunity. An enterprising scavenger like the fox can find so much more food outside chip shops and in dustbins that he can raise more cubs per year than his country cousins who rely on a sparser diet. His fitness is increased by his boldness, and since behaviour is as inherited as most features are, natural selection favours the boldest. Thus urban fox numbers multiply, as the ancient wolves multiplied by sharing shelter with Man and blending their pack organisation and hunting behaviour with the humans’ requirement, till a co-habiting cub could become a pet as well as a hunting companion. The descendent domestic canine, now of many breeds, vastly outnumbers wolves and has spread throughout the world.

A newly created habitat caused by people may lack the charm of pristine wilderness, but it is still an extra habitat.

Introduction of foreign species usually increases biodiversity in their new locations rather than threatening native species, but islands are more vulnerable to indigenous extinctions following human arrival, as is tragically seen in Hawaii, New Zealand, and the Galapagos and Solomon islands. In these high-profile cases the preservation of unique and popular native species is rightly pursued, but many animals and plants transported across the globe find a modest role in their new ecosystem matching the one they came from, alongside the natives. New arrivals sometimes lead to interesting hybridisations, giving rapid rise to new, extra species. Human influence can promote diversification as well as habitat destruction. In fact in 2014 a worldwide collection of 276 studies that compared the biodiversity of farmland with comparable abandoned farms, found more biodiversity on the currently farmed fields, especially in Europe. A newly created habitat caused by people may lack the charm of pristine wilderness, but it is still an extra habitat.

At least we no longer cause extinction by hunting for food as our forbears did, finishing off mammoth, mastodon, auroch, elephant bird, great auk, and dodo. That was sheer predation, but for the most part we first enslave the animals we eat now, and provide their life requirements as inputs from human agriculture and technology, with a cost not in species loss but in climate change. Domestic livestock do not go extinct.

Some nonhuman species also exploit other animals in more subtle ways than predation. European Cuckoos are brood parasites, outsourcing their child care to small birds who pay with their foraging effort as parents, and with their lives as chicks.

Slave-making ants attack a related colony and supplant its queen, so that their own food is provided and their offspring reared by another species. The enslaved nest produces no offspring of its own.

Internal parasites take it further and show specialisations for efficient exploitation of a host for food, shelter and movement. Tapeworms have no gut or digestion of their own nor means of locomotion: they use yours.

The smallest and most artful usurper of another’s resources is a virus, which is merely a genetic ‘instruction leaflet’ on how to build more virus, wrapped in an envelope of lipid and protein. Possessing just a single ‘page’ where an animal’s genes would be an encyclopaedia, the virus can do nothing except insert that page into a cell and impose it on the cell’s complex machinery of life, such that all functions cease except building virus. Its very life is outsourced to a host, the cell whose life it steals. Humans with huge brains may be the most complex thing we know in the Universe, but if there is an evolutionary option for jettisoning all but the simplest parasitic core, then something will take that path, and COVID19 is one such. We are seeing the deadly consequences to its new human host, but we shall survive and perhaps discover a new appreciation of the living things that make up the evolving global ecosystem, of which we are an integral part.

Written by Dr Valerie Jeffries.