Don't come over here! Don't come over here! If you come over here again, I will exterminate your entire clan!

Ever since the ancient continents broke apart, the Bering Strait, located exactly between two oceans (the Arctic and Pacific) and two continents (Asia and America), has been an important node for species dispersal.

Bering Strait | NASA

Over millions of years, the four words "the sea changes and the fields change" are most vividly demonstrated on this land: sometimes the sea water spreads, and huge algae forests drift with the waves; sometimes the tides fade away, and the biting cold wind can only stir the tundra. Such changes have happened again and again, so that the name we call it today - the Bering Strait - can only be regarded as a stage label.

It's so easy to go to the other side of the sea

Adaptation and expansion are the keys to the continuation of every species. When the narrow land bridge across the Bering Strait emerged, endless possibilities emerged to reach the other side of the sea.

Over the past tens of millions of years, this shallow land has witnessed the transformation of Tyrannosaurus Rex heading east into the overlord of America, and has also left behind the hoof prints of horses and camels heading west. However, compared with the spreading torrent of life formed by the thousands of passers-by passing through here, these dazzling stars are insignificant.

So far, there have been at least six amphibian dispersal events, 10 reptile dispersal events, five fungal dispersal events, nine invertebrate dispersal events, five mammalian dispersal events, and 57 plant dispersal events. Each dispersal has almost reshaped the life map of the entire blue planet.

God in the New World

About 750,000 years ago, a group of ancient argali sheep began their adventure to the New World from Siberia, heading south along the mountains on the west side of North America, crossing the sea and mountains.

Bighorn Sheep | pixabay

More than 700,000 years later, a group of primates also set foot on the other side. Perhaps during their wanderings in Siberia, they also hunted the relatives of the former left behind in their hometown. But when the two met in the Yellowstone River Valley in North America, these first humans who came to America must have discovered that the argali in the New World was so different - after 700,000 years of tempering, their horns were larger than those of their relatives.

Bighorn Sheep Mural | Jim Bouldin / Wikipedia

In the harshest deserts and mountains of North America, bighorn sheep wantonly display their tenacity. It is conceivable that such an extraordinary species would shock later generations. It is no wonder that bighorn sheep are always the most frequently appearing characters in the murals of the native peoples of the western United States, and have become a symbol of strength, wisdom and courage in their simple nature worship myths.

The “domestication revolution” and the germ crisis

While humans in the Americas were carving out a sacred tone for bighorn sheep, people and argali in Eurasia were undergoing an epoch-making innovation.

Rice | Pxhere

In the fishing, hunting and gathering era, people were familiar with various species of argali in the Old World. They had long been the main source of meat. However, as the population continued to increase and wild resources gradually shrank, such meat supply could no longer meet demand. The accidental mutation of several wild grasses opened the prelude to agricultural civilization. With abundant food supply, people were able to and had begun to try to bring wild animals into their daily lives.

The argali sheep living in Central Asia became one of the first species to succeed in this "domestication revolution". To this day, its domesticated offspring, sheep, continue to show their value on each of our dining tables and wardrobes.

Sheep tamed by humans | pixabay

But as Jared Diamond reviews in Guns, Germs, and Steel, the domestication and breeding of livestock reshaped human society in every way, bringing not only convenience but also germs.

At least 65% of human diseases today can be traced back to zoonotic diseases. However, after paying a lot of price, our immune system has been able to calmly face the threats of many zoonotic diseases. For the Native Americans who have never experienced this long confrontation, the germs from livestock are still like the fierce god of death. In the stories of the conquest of America during the Age of Exploration, there are stories everywhere about the ancient indigenous civilizations being defeated by the germs carried by the conquerors (not just steel and guns).

If humans in the New World were losing ground to zoonotic diseases, then would bighorn sheep, which are from the same family as sheep, also face the threat of these sudden invading diseases?

The answer is of course yes.

The sheep came, and so did the germs

In fact, in the more than 10,000 years since humans arrived in America, many native species were unable to adapt to the existence of this efficient hunter and died out one after another. Although bighorn sheep play a special role in indigenous mythology and are also facing the threat of hunting, they still have a population of nearly 2 million in the early 19th century. This is inseparable from their strong adaptability to the environment and their vigorous vitality.

Bighorn Sheep | pixabay

However, between 1870 and 1950, the population of bighorn sheep began to collapse. This was largely related to the development of animal husbandry near their habitat: European colonists brought sheep and many pathogens that lurked in the herds, among which Mycoplasma ovipneumoniae was the most deadly. Statistics over the years have found that bighorn sheep herds in some areas would lose more than 90% of their members due to an epidemic. With the development of animal husbandry in the western United States, such epidemics are still increasing.

Ranch | pixabay

The great migration of organisms (including humans, of course) after the Age of Discovery is actually also a form of biological diffusion, but compared with the story that took place over millions of years on the Bering Land Bridge, they are fundamentally different.

Naturally driven biological dispersal events have proven that bighorn sheep are not a weak species, but even they have difficulty coping when faced with more violent human-induced dispersal events.

This story may serve as a warning to us, reminding us that human activities can have such profound impacts on the world, and reminding us that we should act more cautiously in the years to come.

This article comes from the Species Calendar, welcome to forward