Far fewer bee species are buzzing across Earth today, following a steep decline in bee diversity during the last three decades, according to an analysis of bee collections and observations going back a century.  

About half as many bee species are turning up in current collecting efforts for museums and other collections compared with in the 1950s, when surveys counted around 1,900 species a year, scientists report December 10 at bioRxiv.org. That high diversity in collections endured for several decades, but then began to plummet around the 1990s, likely reflecting a real drop in global bee diversity, according to the study, which is under peer review. 

“This is the first study suggesting that bee decline is a global process, and that the most significant changes have occurred in recent years,” says Margarita López-Uribe, a bee evolutionary ecologist at Penn State who was not part of the new research. 

The new work evaluates global trends in bee diversity since the 1920s by tapping the database of the Global Biodiversity Information Facility. This international data-sharing network holds what López-Uribe describes as “the most comprehensive dataset of insect collection records worldwide,” including photos of bees in the field and of museum specimens dating back to the 18th century. Previous bee studies have reported falling populations, but evidence has often been limited to Europe and North America. Numbers of western honeybees (Apis mellifera) have been decreasing in North America and Europe (SN: 6/20/19), for example, but have increased in Asia, Africa and South America. For bees overall, though, the global situation was unclear.

Eduardo Zattara and Marcelo Aizen of the Pollination Ecology Group at the Biodiversity and Environment Research Institute in Rio Negro, Argentina, found that the number of instances of observing bees has climbed in recent decades, probably due to more researchers going into the field to document and study bees. 

But the number of observed species fell. In the 1950s, collectors added about 22,000 bee records per year, of about 1,900 species each year, for a global total of 5,600 species collected over the whole decade. After correcting for sampling effort, the researchers estimate that about 6,700 species would have been found in the wild. In the 2010s, collectors tallied an average of 860 species per year from an average of more than 37,000 observations per year, leading to an estimate of only about 3,400 species to be found worldwide in the wild.

Declines in the number of species occurred on nearly every continent, starting at various points in the last four decades but largely in the 1990s on most continents. One exception was Australia and nearby islands, where the number of bee species estimated from observations spiked from about 300 to 500 in the 2000s. But species numbers in that region dropped back to 300 in the 2010s. Globally, thousands of bee species have become so rare that they are difficult to find or have gone extinct. 

These findings should convince people that bee diversity losses are not confined to specific regions, but “part of larger, worldwide trend,” says Zattara, who is now a visiting scientist at the Smithsonian National Museum of Natural History in Washington, D.C.

While the study provides an “invaluable” overview, the dataset is surely missing important insect collections from Asia, says bee biologist Natapot Warrit of Chulalongkorn University in Bangkok. He hopes the study encourages other researchers in the region to study and share data on pollinators. 

Bees and other insects such as butterflies and flies pollinate more than 75 percent of the most important crop types grown today, scientists say. But these pollinators face multiple threats including the expansion of monoculture crop cultivation, pesticides (SN: 1/17/18), climate change (SN: 9/24/15) and pathogens that can spread with the international bee trade (SN: 1/18/19). Researchers also have suggested bees may be at risk from power lines (SN: 11/12/19).

While their study reveals an ongoing “major global collapse in bee diversity,” the researchers aren’t trying to sound “gloomy or apocalyptic,” Zattara says. Rather, they hope the study prompts other scientists, policy makers and business leaders take action to reverse the decline.

Four ancient youngsters, one pair from around 8,000 years ago and another from about 3,000 years ago, have opened a window on humankind’s far older, far-flung African origins. 

Analyses of the west-central African children’s DNA indicate that at least three major human lineages —ancestral to either today’s central African hunter-gatherers, southern African hunter-gatherers or all other present-day people — genetically diverged from each other in rapid succession between roughly 250,000 and 200,000 years ago. 

A fourth, previously unknown human population also emerged in that time span and left a small genetic mark on modern western and eastern Africans, a team led by evolutionary geneticists Mark Lipson and David Reich, both of Harvard Medical School, reports online January 22 in Nature. That human line possessed a small amount of DNA from hominid populations that had originated before the rise of the human species, possibly Neandertals.

“This quadruple radiation [of human lineages] had not been identified before from DNA,” Reich says.

That genetic evidence from the long-dead kids fits a scenario in which different Homo sapiens populations emerged in different parts of Africa as early as around 300,000 years ago, followed by a mixing and mingling of populations across the continent (SN: 9/28/17).

A previous genetic study, led by evolutionary geneticist Pontus Skoglund of the Francis Crick Institute in London, identified a human population originating more than 200,000 years ago that was ancestral to later rainforest hunter-gatherer groups in western and central sub-Saharan Africa. The new study provides further evidence for that ancestral line: Ancient children in the new study carried a minority of ancestry from those ancient forerunners of rainforest groups.

Genetic data in the new study provide “the only ancient DNA record from so far west in sub-Saharan Africa,” Skoglund says.

Lipson’s group extracted DNA from four children buried at Shum Laka, a rock-shelter in northwestern Cameroon. Excavations there in the 1980s and 1990s yielded stone tools and other artifacts from hunter-gatherers spanning the last 30,000 years. The site also served as a cemetery for extended families. A total of 18 human skeletons, most from children, have been unearthed at Shum Laka. Some burials date to about 8,000 years ago, others to around 3,000 years ago.

The four Shum Laka children who yielded DNA — three boys and a girl — ranged in age at the time of death from around 4 to 15 years old.

Based on linguistic and archaeological evidence, researchers generally consider the region of Cameroon that includes Shum Laka to have been the place where Bantu languages, spoken by many Africans today, originated and spread across the continent’s southern half after around 4,000 years ago. The Bantu expansion is thought to explain why the majority of people in that swath of Africa now display close genetic connections.

Intriguingly, current Bantu speakers are not closely related to the Shum Laka children, the researchers say. The ancient kids inherited about two-thirds of their DNA from a previously unknown population distantly related to present-day West Africans. The rest of the genetic material came from the lineage outlined in the earlier Skoglund-led study that was ancestral to hunter-gatherers now living in central Africa. Present-day central African hunter-gatherers have a different ancestry from most Bantu speakers today. 

As a result, Bantu speakers across Africa likely didn’t descend from the ancient Shum Laka population, the researchers say. But other human groups could have lived in west-central Africa around the same time, including some who conversed in early Bantu tongues, Lipson and his colleagues speculate.

Another provocative new discovery concerns one of the Shum Laka youngsters, an adolescent male buried around 8,000 years ago. That boy possessed a rare set of Y chromosome gene variants, which are passed from father to son. It’s the first known ancient DNA from this unusually old paternal lineage. Today, this particular paternal lineage is found almost nowhere outside of two ethnic groups in western Cameroon today. Previous research suggests this male genetic line dates back to between 200,000 and 300,000 years ago, making it the oldest one known. It’s unclear why only one of the three ancient African boys in the new study came from that ancient male line of descent.