Humans Began Dramatically Changing Nature as Early as 6,000 Years Ago

December 21, 2015 | Joanne Kennell

Man walking along the top of a rusty pipeline
Photo credit: Unsplash/Pixabay

We’ve been altering life on Earth for longer than we thought.

It is nothing new to hear that humans dramatically, often negatively, shape the face of the planet.  Concerns about climate change, loss of biodiversity, pollution and habitat destruction are seen daily in most new outlets, and new research points to this happening even earlier than previous known — 6,000 years ago.

A new study published Wednesday (December 16) in Nature suggests that human activities caused a major shift in plant and animal community structures nearly 6,000 years ago — after the start of the “Holocene,” a geological era which includes the growth of human populations around the world.

Scientists from the Smithsonian Museum of Natural History compared data from the fossil record of 360,000 organisms with observations from after the rise of humans to better understand how humans have changed life on Earth.

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They investigated 80 different plant and animal communities on different continents throughout the past 307 million years by examining both “aggregated” and “segregated” pairs.   Aggregated pairs are those that show up in the same place together more than one would statistically expect to happen, and segregated pairs are those that are separated more than would be expected by chance.  When either of these happen, it suggests there is some environmental pressure or force keeping the species together or driving them apart.

It turns out that from 307 million years ago up to the beginning of the Holocene, aggregated species pairs were more prevalent on Earth.  However, about 6,000 years ago there was a shift that led to segregated pairs becoming more dominant.  So what changed?

Researchers had two main theories: either changes in climate or some kind of biological pressure, likely human activities, were responsible.  They were able to rule out climatic pressures by examining the composition of ice cores taken from the polar ice caps.  Scientists can learn a lot about Earth’s climate through ice caps, and they were able to conclude that while the climate did vary over millions of years, there were no major shifts in plant and animal communities.  So guess what that leaves?  Yep, humans.

At this time, human populations were growing, and agriculture practices were on the rise in North America (where most of the data from the study came from).  “I do want to emphasize [that] we don’t have a smoking gun of mechanisms for what activities humans were doing,” said the paper’s lead author, S. Kathleen Lyons, a paleobiologist at the Smithsonian Institute’s Evolution of Terrestrial Ecosystem’s program to The Washington Post.

Lyons added that some species were probably unable to compete with humans for food or space, and species that were once found together were being forced apart to adapt to humans changing the landscape.  Was this shift good or bad?  There is no definite answer, but this information can be useful in predicting how species will react to further stresses in the future.

Furthermore it is important to recognize the powerful influence humans have on the environment, both then and now and to “wake up” to further changes we may cause.

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