Wednesday, December 30, 2020

DNA Study of Caribbean Islanders Yields Surprises


These pieces reveal a range of styles and date to around 1200 A.D. 
(Corinne Hofman and Menno Hoogland / Florida Museum of Natural History)

New DNA studies have clarified migrations to islands of the Caribbean, but also raise additional questions. One question is why the European explorers of those island believed the native population to be much higher than the studies indicate?

This report on a technique developed by Harald Ringbauer, a postdoctoral fellow in the Reich Lab, explains that shared segments of DNA were used to estimate past population size, and showed that only about 10,000 to 50,000 people were living on two of the largest islands, Hispaniola and Puerto Rico, shortly before European arrival.

"While the heat and humidity of the tropics can quickly break down organic matter, the human body contains a lockbox of genetic material: a small, unusually dense part of the bone protecting the inner ear. Primarily using this structure, researchers extracted and analyzed DNA from 174 people who lived in the Caribbean and Venezuela between 400 and 3,100 years ago, combining the data with 89 previously sequenced individuals.

The team, which includes Caribbean-based scholars, received permission to carry out the genetic analysis from local governments and cultural institutions that acted as caretakers for the human remains. The authors also engaged representatives of Caribbean Indigenous communities in a discussion of their findings.

The genetic evidence offers new insights into the peopling of the Caribbean. The islands' first inhabitants, a group of stone tool-users, boated to Cuba about 6,000 years ago, gradually expanding eastward to other islands during the region's Archaic Age. Where they came from remains unclear -- while they are more closely related to Central and South Americans than to North Americans, their genetics do not match any particular Indigenous group."
The new study suggests the Caribeean islands were first populations by two waves. A group of migrants almost totally replaced the islands’ original population. Only 3 of the individuals sampled showed ancestry of two distinct populations.

Dr. William F. Keegan, whose work in the Caribbean spans more than 40 years, contributed to the study. He is curator at the Florida Museum of Natural History and co-senior author of the study. "The methods David's team developed helped address questions I didn't even know we could address."

The Arawak-speakers who arrived on these islands from northeast South America introduced ceramics about 2500 years ago. 
"During the Ceramic Age, Caribbean pottery underwent at least five marked shifts in style over 2,000 years. Ornate red pottery decorated with white painted designs gave way to simple, buff-colored vessels, while other pots were punctuated with tiny dots and incisions or bore sculpted animal faces that likely doubled as handles. Some archaeologists pointed to these transitions as evidence for new migrations to the islands. But DNA tells a different story, suggesting all of the styles were developed by descendants of the people who arrived in the Caribbean 2,500-3,000 years ago, though they may have interacted with and took inspiration from outsiders.

"That was a question we might not have known to ask had we not had an archaeological expert on our team," said co-first author Kendra Sirak, a postdoctoral fellow in the Reich Lab. "We document this remarkable genetic continuity across changes in ceramic style. We talk about 'pots vs. people,' and to our knowledge, it's just pots."

Read the full report here: Ancient DNA retells the story of Caribbean's first people, with a few plot twists; Pre-Columbian Pottery in the West Indies; Old World Migrations to the Americas

Thursday, December 17, 2020

The Crazy Colorado River

Recent geological research indicates that the Colorado river's route from the Colorado Plateau was influenced by tectonic deformation and vaciliating sea levels that caused a series of stops and starts between 6.3 and 4.8 million years ago. A team led by geologist Rebecca Dorsey of the University of Oregon has made a case for a complex history of the river, showing that, contrary to conventional thinking, a river's connection to the ocean is not a once-and-done deal.

"The birth of the Colorado River was more punctuated and filled with more uneven behavior than we expected," Dorsey said. "We've been trying to figure this out for years. This study is a major synthesis of regional stratigraphy, sedimentology and micropaleontology. By integrating these different datasets we are able to identify the different processes that controlled the birth and early evolution of this iconic river system."

Dorsey said that no single process controlled the Colorado River's initial route to the sea. "Different processes interacted in a surprisingly complicated sequence of events that led to the final integration of that river out to the ocean," she said.

The region covered in the research stretches from the southern Bouse Formation, near present-day Blythe, California, to the western Salton Trough north of where the river now trickles into the Gulf of California. The Bouse Formation and deposits in the Salton Trough have similar ages and span both sides of the San Andreas Fault, providing important clues to the river's origins.

The Colorado River starts in the peaks of the Rocky Mountain in the United States and flows into Mexico, where it empties into the Upper Sea of Cortez. Its natural course has varied over thousands of years, and the demand for water to serve an estimated 40 million people now exceeds the river’s supply, resulting in the desiccation of the Colorado’s last hundred miles.

The Colorado River's seven basin states are managing water under the Drought Contingency Plan, an agreement to safeguard water levels at the river's two main reservoirs, Lake Mead and Lake Powell. The two lakes are critical to providing water in times of drought. The Colorado River Basin states are Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.