Dan Flores

Some of those human migrations may have been related to the reshuffling of American nature that took place in the echoes of the Pleistocene extinctions. The biology of the continent was reinventing itself. The vegetation was changing. Without ground sloths to disperse their seeds, the range of Joshua trees now began to contract. And without mammoths to curb them, honey mesquite began to spread.

There were so many missing animals that a remarkable number of ecological niches either were vacant or newly filling. The ecological rebirth was most dramatic in the western half of America. The loss of mammoths, giant bison, horses, camels, ground sloths, dire wolves, short-faced bears, scavenging birds, and a range of cat predators opened niches at every level.

There were so many missing animals that a remarkable number of ecological niches either were vacant or newly filling. The ecological rebirth was most dramatic in the western half of America. The loss of mammoths, giant bison, horses, camels, ground sloths, dire wolves, short-faced bears, scavenging birds, and a range of cat predators opened niches at every level.

There were so many missing animals that a remarkable number of ecological niches either were vacant or newly filling. The ecological rebirth was most dramatic in the western half of America. The loss of mammoths, giant bison, horses, camels, ground sloths, dire wolves, short-faced bears, scavenging birds, and a range of cat predators opened niches at every level.

In cases like wolves and bears, there were ready replacement species. With dire wolves now extinct, gray wolves and ancient American wolves emerged as the primary canid predators. But with 70% of America's grazers gone, niches for replacements were wide open. With almost no competition, a new, smaller bison supplanted horses, mammoths, and its huge bison ancestors.

In cases like wolves and bears, there were ready replacement species. With dire wolves now extinct, gray wolves and ancient American wolves emerged as the primary canid predators. But with 70% of America's grazers gone, niches for replacements were wide open. With almost no competition, a new, smaller bison supplanted horses, mammoths, and its huge bison ancestors.

In cases like wolves and bears, there were ready replacement species. With dire wolves now extinct, gray wolves and ancient American wolves emerged as the primary canid predators. But with 70% of America's grazers gone, niches for replacements were wide open. With almost no competition, a new, smaller bison supplanted horses, mammoths, and its huge bison ancestors.

Within a few centuries, this new dwarf bison grew into a biomass of animals that had almost no analog anywhere else on Earth. Biologists now believe modern bison are a classic example of anthropogenic selection, their size and rapid reproduction shaped by human predation.

Within a few centuries, this new dwarf bison grew into a biomass of animals that had almost no analog anywhere else on Earth. Biologists now believe modern bison are a classic example of anthropogenic selection, their size and rapid reproduction shaped by human predation.

Within a few centuries, this new dwarf bison grew into a biomass of animals that had almost no analog anywhere else on Earth. Biologists now believe modern bison are a classic example of anthropogenic selection, their size and rapid reproduction shaped by human predation.

Seals, sea otters, and sea lions excepted, along with the one-pronghorn species that survived to browse the forbs that camels once ate, most of the large animals west of the Mississippi were Asian immigrants. In some parts of the planet, the warmer climate that marked the end of the ice ages allowed hard-pressed humans to try out some new things.

Seals, sea otters, and sea lions excepted, along with the one-pronghorn species that survived to browse the forbs that camels once ate, most of the large animals west of the Mississippi were Asian immigrants. In some parts of the planet, the warmer climate that marked the end of the ice ages allowed hard-pressed humans to try out some new things.

Seals, sea otters, and sea lions excepted, along with the one-pronghorn species that survived to browse the forbs that camels once ate, most of the large animals west of the Mississippi were Asian immigrants. In some parts of the planet, the warmer climate that marked the end of the ice ages allowed hard-pressed humans to try out some new things.

But since humans had extensively settled America only 13,000 years ago rather than 45,000, North America didn't yet call for an agricultural revolution the way the old world did. America's human cultures segued to a stage where animals were still of primary importance, but plants were taking on a more significant role.

But since humans had extensively settled America only 13,000 years ago rather than 45,000, North America didn't yet call for an agricultural revolution the way the old world did. America's human cultures segued to a stage where animals were still of primary importance, but plants were taking on a more significant role.

But since humans had extensively settled America only 13,000 years ago rather than 45,000, North America didn't yet call for an agricultural revolution the way the old world did. America's human cultures segued to a stage where animals were still of primary importance, but plants were taking on a more significant role.

Archaic is the term anthropologists and archaeologists have long used for humans living this way, by which they mean people existing as hunter-gatherers. So while the old world experimented with agriculture and domestication, in North America, the hunting-gathering lifestyle continued over vast spans of time and diverse geographies all the way into modern history.

Archaic is the term anthropologists and archaeologists have long used for humans living this way, by which they mean people existing as hunter-gatherers. So while the old world experimented with agriculture and domestication, in North America, the hunting-gathering lifestyle continued over vast spans of time and diverse geographies all the way into modern history.

Archaic is the term anthropologists and archaeologists have long used for humans living this way, by which they mean people existing as hunter-gatherers. So while the old world experimented with agriculture and domestication, in North America, the hunting-gathering lifestyle continued over vast spans of time and diverse geographies all the way into modern history.

Clearly, we ancient hunters of animals surrendered our oldest life away with reluctance. America wasn't just in the throes of biological recreation. Around 8,500 years ago, there was another potent change. The warming cycle that ended the last ice age didn't relent, and America's climate swung into a hot, dry phase that stayed in place for a mind-blowing 3,700 years.