In this series, The Week looks at the ideas and innovations that permanently changed the way we see the world. This week, the spotlight is on ecology:

Ecology is the branch of biology concerned with the study of interactions between natural systems.

One core goal of ecology is to understand the distribution and abundance of living things in the physical environment, saysAmerican non-profit organisation theKhan Academy.It investigates the patterns in nature [that] are driven by interactions among organisms as well as between organisms and their physical environment.

Ecology is concerned with two main factors - biotic, which is living-organism-related, and abiotic, which considers nonliving or physical systems.

Ecology developed as a prominent strand of scientific investigation only in the second half of the 20th century, but ecological thinking has been around for millennia, says the Environment and Ecology website.

A form of ecology started with the Ancient Greeks, around 2,400 years ago. Theophrastus, a friend and associate of Aristotle, first described the interrelationships between organisms and their environment, according to theEncyclopedia Britannica.

Modern ecology arguably started with the publication of The Oeconomy of Nature by Swedish botanist Carolus Linnaeus in 1749.Linnaeus made the argument that if one looks closely at nature it is clear that even the simplest organisms have an important role to play in this natural economy; that no living thing is useless, says Encyclopedia.com.

German explorer and scientist Alexander von Humboldt advanced these beliefs, devising the theory that nothing in nature could be studied in isolation and all phenomena were connected.

But it is Darwin whose work most significantly expanded the field of ecology, and it is often held that the roots of scientific ecology may be traced back to Darwin, says Environment and Ecology.

On the Origin of Species is full of observations and proposed mechanisms that clearly fit within the boundaries of modern ecology and the term ecology was coined in 1866 by a strong proponent of Darwinism, Ernst Haeckel.

The 20th century brought huge leaps forward in the scientific study of plants and their environments, through groups of botanists in the US and in Europe.

The European botanists concerned themselves with the study of the composition, structure, and distribution of plant communities. The American botanists studied the development of plant communities, or succession, says Encyclopedia Britannica.

The British ecologist and conservationist Arthur Tansley developed the view that since plants exist in communities the ecologist should be concerned with the structure of communities, or plant sociology, says Oxford Reference.

Tansley then coined the term ecosystem in 1935, recognising that it was not possible to consider organisms without considering their physical environment.

Ecosystem ecology became one of the principal forces in ecology in the 1960s and 1970s and the basis of a new theoretical ecology termed systems ecology, says Encyclopedia.com.

Human ecology has become a distinct and important field of study in recent years, as more weight is given to the consideration that humans are a major ecological factor.

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Ecology helps us understand the environment and humans relationship with it, something that is vital for food production, maintaining clean air and water, and sustaining biodiversity in a changing climate, says the British Ecological Society.

The human ecological impacts of climate change are key to understanding the future of the human species, and harnessing that understanding could be critical for human longevity, adds Dr Roger Rosenblatt in the Annals of Family Medicine.

Everything that we have accomplished in the fields of medicine and public health could be undermined if we do not pay attention to these rapid environmental changes, says Rosenblatt. By staying engaged in the natural world, we can help to prevent the collapse of the biological systems upon which we all depend.

Ecological research can also feed into the prevention of human disease. Earlier this month, scientists in Kenyadiscovered a microbe carried by some mosquitos that prevents the insects from being infected with malaria parasites - and by extension, from transmitting the deadly disease to humans.

As well as its importance to human survival, understanding ecology is important to nature conservation and the survival of a broad range of species.

Ecology allows us to understand the effects our actions have on our environment, says Conserve Energy Future.

With this information, it helps guide conservation efforts by first showing the primary means by which the problems we experience within our environment begin and by following this identification process, it shows us where our efforts would have the biggest effect.

Ecology is the foundation of how we can use Earths resources in ways that leave the environment healthy for future generations, says the Ecological Society of America.

Without ecological understanding, we could not protect humans, animals, the environment - it matters now and will continue to matter.

Read more:

52 ideas that changed the world - 49. Ecology - The Week (UK)