If you took a cruise along the northern stretch of the Nile some 6,000 years ago, you wouldn't have seen any pyramids, but you might have spotted a giraffe or an elephant taking a drink at the bank of the river.
At that time, the Nile wasn't surrounded by desert; rather, the warmer, wetter landscape resembled the current scenery of sub-Saharan East Africa.
Today, Egypt's elephants and giraffes are extinct. So are its cheetahs and aurochs and wildebeests. But animal bones and images of animals on ancient artifacts reveal what creatures once roamed the region. A team of researchers looked at Egypt's rich archaeological record and found that most mammal extinctions over the last six millennia were linked to periods of big change in terms of climate and human civilization. [Wipe Out: History's Most Mysterious Extinctions]
Justin Yeakel — a researcher out of the University of California, Santa Cruz, who is now a postdoctoral fellow at the Santa Fe Institute in New Mexico — said the work was first inspired by a trip with a colleague to see a traveling exhibit on King Tutankhamun while it was in San Francisco a few years ago.
"We were just amazed at the diversity of animals in the artifacts," Yeakel told Live Science. "It got us thinking about how we could use representations of animals in the historical record to understand how animal communities have changed."
Egypt turned out to be a good area for a case study, because the area has been occupied continuously for thousands of years and has an extensive archaeological record. There are rock art drawings of hippopotamuses and rhinoceroses from the early Holocene. The tombs of Egyptian pharaohs are decorated with hunting scenes that show which creatures would have been prized prey. Import records of cheetahs and lions reveal when certain animals might have been considered exotic after disappearing locally.
The researchers found that Egypt was home to 37 large-bodied mammals (those over 8.8 lbs., or 4 kilograms) during the Late Pleistocene and early Holocene. Today, just eight of those creatures remain: the golden jackal, the ibex, the Barbary goat, the Egyptian fox, the Dorcas gazelle, the wild ass, the striped hyena and the slender-horned gazelle, which is on the verge of extinction.
"Our simplest observation was that the community changed in a very nonrandom way," Yeakel said.
The stability of the ecosystem tended to unravel during periods of major climate change and socio-political turnover, the scientists found. When the so-called African Humid Period ended about 5,000 years ago, Egypt's landscape switched to a drier, desertlike climate; around the same time, humans started farming and ancient Egypt's Dynastic Period began. Another aridification period occurred about 4,170 years ago and has been linked to the collapse of Egypt's Old Kingdom, the period that saw the first pyramids. A third drying period has been linked to the fall of the New Kingdom in Egypt about 3,000 years ago.
Yeakel said he and his fellow researchers can't really tease apart the possible causes that led to these ecological changes. But the scientists have identified the potential drivers. During the first big change after the African Humid Period, for example, human populations grew and overhunting might have driven the decline of large herbivores — such as elephants, giraffes and native camels — which then indirectly affected the populations of the predators that ate the herbivores. Agriculture was also on the rise during this period. Most of the region's nutrients were concentrated in the Nile floodplain, and competition with farmers might have also hurt herbivore populations. A third possible driver could have been the climate; the drier environment might have limited the availability of plants at the bottom of the food chain.
The changes humans are inducing in the environment now are probably fundamentally different from the factors that drove ecological changes in the past, Yeakel said. Nonetheless, studying past changes is the only way scientists can predict what will happen in the future.
"We have to look at ecosystems as a continuum," Yeakel said. "We can't just look at the modern ecosystem. We have to look at how it has functioned in the past and how has it changed over time to establish a baseline for how the system will change in future."
The findings were published today (Sept. 8) in the journal Proceedings of the National Academy of Sciences.