Chapter 1: Ancient Wetlands as Humanity's Cradle

A provocative new study posits that the roots of modern humans can be traced back to ancient wetlands in Africa, a claim that has sparked skepticism from various researchers.

Vanessa Hayes, a geneticist at the Garvan Institute of Medical Research, found herself reflecting on the significance of her aerial view over northern Botswana's Makgadikgadi Pans earlier this year. This immense salt flat, once part of Africa's largest lake, still bears the imprints of its shoreline and fault lines, remnants of the tectonic activities that reshaped the region. Hayes believes this area was the cradle of humanity—the very place where modern human ancestors first emerged.

Her research team examined the DNA of 1,271 individuals from southern Africa, an area marked by unique genetic diversity that remains largely unexplored. Through this genetic analysis, the team constructed a family tree that suggests anatomically modern humans first appeared in the Makgadikgadi wetlands approximately 200,000 years ago. They propose that these early humans remained in this region for about 70,000 years before climatic changes prompted migrations throughout Africa and eventually to other continents.

However, Hayes's assertions have ignited controversy. Critics argue that her study relies on a limited dataset, focusing solely on contemporary DNA while neglecting ancient genomes, fossils, and cultural artifacts that may indicate an earlier and more complex history of human evolution. Eleanor Scerri, an archaeologist at the Max Planck Institute for the Science of Human History, contends that such a narrow focus overlooks substantial evidence pointing to an older origin of our species.

"The conclusions are far-fetched and greatly exaggerated," asserts Carina Schlebusch, a geneticist specializing in southern Africa. "This study provides insights into only a minute portion of the human genome, lacking broader implications for our species' origins."

The DNA analyzed primarily represents the mitochondrial genome, which is inherited only from mothers. The ancestral family tree of human mitogenomes is rooted in Africa, splitting into two major branches: L0, predominantly found among southern African populations like the Khoe and San, and L1, encompassing the majority of other human groups. Despite the focus on L0, there remains a significant gap in our understanding of the genetic diversity within this lineage, as much research has concentrated on populations in Western countries.

Hayes's team aimed to address this gap by identifying individuals who represented the lesser-known sub-branches of L0, ultimately adding approximately 200 new mitogenomes to an existing dataset of 1,000. By analyzing this expanded dataset, Hayes's colleague Eva Chan estimated that the L0 lineage likely emerged in Makgadikgadi around 200,000 years ago. They argue that this lineage remained largely stable for nearly 70,000 years, coinciding with a period of extreme drought that would have rendered the wetlands an isolated sanctuary.

As noted by Chiara Barbieri, a geneticist and anthropologist at the University of Zurich, while this information is valuable, it is challenging to accurately pinpoint the origins of the L0 lineage solely based on modern DNA. "To truly anchor genetic variation in time and space, we need carbon-dated fossil DNA," she explains, an aspect that Hayes's research did not incorporate.

Furthermore, the focus on contemporary mitogenomes limits the ability to construct comprehensive narratives about human ancestry, according to Scerri. "Attempting to reconstruct deep ancestry from mitochondrial DNA is akin to piecing together a language using just a few words."

When examining different genomic components, divergent narratives arise. For instance, the Y chromosome family tree points to a root in Cameroon, situated 2,000 miles northwest of the proposed homeland. Additional studies of complete genomes indicate that the ancestors of today's Khoe and San diverged from other African populations between 350,000 and 260,000 years ago, predating Hayes's suggested timeline for human origins. Another analysis of complete genomes even indicates even older divergences. Katerina Harvati, a human evolution researcher at the University of Tubingen, notes the lack of reference to these earlier studies in Hayes's paper.

These conflicting findings suggest that humanity's narrative in Africa is far more intricate than proposed, indicating prolonged mixing and diversification among our species. Fossil evidence also supports this complexity. For example, bones discovered in a Moroccan cave, dated to 315,000 years ago, represent the oldest known Homo sapiens remains. Additionally, a 180,000-year-old jawbone from Misliya Cave in Israel indicates that humans left Africa much earlier than Hayes's timeline. Recent findings, such as a 210,000-year-old skull from Apidima Cave in Greece, further affirm that Homo sapiens had already expanded significantly before the period defined by Hayes.

Many scientists have therefore moved away from the simplistic notion that humanity originated in a single African region. Instead, they advocate for the concept of African multiregionalism, which posits that the traits of modern humans developed in a mosaic fashion across the continent, with diverse ancestors gradually intermingling. This perspective explains the simultaneous emergence of human fossils and advanced tools across various locations.

Although Hayes's research does not directly dismiss archaeological findings, she emphasizes her focus on anatomically modern humans, which she refers to as Homo sapiens sapiens. She posits that while other human species may have existed throughout Africa, they represent "breakoff lineages that came and went," with only those in her defined homeland ultimately contributing to present-day humans.

"This is a convenient response," counters Scerri, "but it lacks convincing evidence." The defining features of modern humans did not coalesce in any single individual until between 100,000 and 40,000 years ago, well after the emergence of our species and the migrations Hayes describes. A more nuanced understanding of human origins suggests that multiple ancestral lines contributed to our history.

Hayes is no stranger to controversy. In 2010, she published the complete genomes of four San elders from Namibia, aiming to enhance the representation of southern Africans in genetic research. However, this decision drew criticism from the Working Group of Indigenous Minorities in Southern Africa (WIMSA), which accused her team of arrogance and cultural insensitivity. Although Hayes had obtained verbal consent from the participants, San leaders questioned the adequacy of this consent and criticized the use of derogatory terms and personal data without proper engagement.

In response to this incident, the South African San Council has established ethical guidelines for researchers working with their communities, emphasizing the importance of involving the San in research design and respecting their culture.

Hayes asserts that she has collaborated with the communities in her latest study for a decade, ensuring they fully understood the purpose of their participation. She plans to meet with the San Council's directors soon and recently returned to the communities involved in her research to share her findings.

But given the response to her study, it seems that the scientific community may present a more formidable challenge.