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Understanding the environment: Co-evolution
Understanding the environment: Co-evolution

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Reading 6.5: Co-evolution

In Readings 3.5 and 4.4, I introduced the connected ideas of interdependence and homeostasis. It can now be seen that homeostasis is just another aspect of regulation and control that was considered in Reading 4.4, in the situation where the parts of a system, the subsystems, act on each other to produce a stabilising effect. In this section, you have considered the animal managing its environment, but of course this perspective applies to any and every plant and animal in the environment. Taking a view from the outside of a particular ecological system you can consider each animal and plant as the component of a system. Each node takes inputs from a set of other nodes, processes those inputs, and provides outputs to a further set of nodes. All is dynamic. As one particular animal or plant modifies its environment, so its environment modifies the animal or plant in the feedback loop you have identified. So you must consider the environment managing the animal or plant, as much as the animal or plant managing the environment.

To survive, each system must continually adjust itself in order to maintain its particular role or roles in the ecosystem – it must maintain relationships that enable it to survive and prosper as an individual until it reproduces. The species must also maintain relationships with other species so that it may survive and prosper within the changing ecosystem.

There is no greater example of co-evolution than planet Earth. Just compare Earth’s atmosphere with those of Venus and Mars. Earth has an atmospheric carbon dioxide concentration just above 0.03 per cent, while Venus and Mars have atmospheric concentrations of carbon dioxide of 98 per cent and 95 per cent respectively; and what about average surface temperatures? Earth 13 °C, Venus 477 °C, Mars -53 °C, and yet Earth is situated between Mars and Venus, and so you might expect a temperature around the mean of these two, around 265 °C. Four billion years ago, Earth also had an atmospheric concentration of 98 per cent carbon dioxide. Its surface temperatures were also extreme. So what happened? Life! Look at almost every component of the Earth system and you see the influence of life. Planet Earth has co-evolved with life. The Solar system, including the three planets above, was created about 4.6 billion years ago; evidence of the first living cells on Earth dates back to 3.6 billion years ago. These thrived in the carbon-dioxide rich atmosphere, but suddenly, about two billion years ago, a few bacteria evolved the ability to photosynthesise – to combine carbon dioxide, water and solar energy to create structural materials and food sources. The rapid proliferation of photosynthetic bacteria, radically transformed the atmospheric composition of gases to be dominated by nitrogen (78 per cent) and oxygen (21 per cent). Carbon was removed from the atmosphere and deposited as carboniferous rocks (the calcium carbonate skeletons of phytoplankton) and, to a lesser extent, as coal, petrol and gas. The high concentrations of oxygen in the atmosphere allowed the development of the ozone layer – a protective blanket shielding the Earth’s surface from deadly levels of ultraviolet light. Living organisms were finally able to evolve on land. Almost everything that you come across – the air that you breathe, the water that you drink, the soil that you walk on – is there thanks to billions of years of co-evolution between living organisms and planet Earth: a life sustaining and promoting feedback relationship.

Rather than competition, the overriding message you get from living things around you is cooperation. Life has evolved increasingly complex mechanisms of sustaining itself in the face of environmental disturbance and change. Co-evolution is all about developing ever-increasing supporting feedback mechanisms. Are shared models of supportive co-evolution, rather than cut-throat competition, something we can learn from nature and transpose to human activity systems?