Neanderthals and Denisovans, our ancient human relatives, coexisted with early Homo sapiens and interbred, leaving a lasting impact on our genetic makeup. Recent advances in ancient DNA analysis are revealing the extent of their influence on our biology. Traits inherited from these ancient cousins persist in us today, shaping various aspects of our lives, from fertility to immune responses and even how we handle viruses like COVID-19.
Mary Prendergast, an archaeologist at Rice University, notes that we are now uncovering the genetic legacies of these ancient humans and exploring their implications for our health and bodies.
In recent months, researchers have linked Neanderthal DNA to diverse human traits, such as a hand disease and the shape of our noses. They’ve even introduced Neanderthal and Denisovan genes into mice to study their biological effects, which included larger heads and an extra rib in the mice.
While many mysteries still surround our human journey, Dr. Hugo Zeberg of the Karolinska Institute in Sweden highlights that emerging technologies, research, and collaborations are helping scientists address fundamental questions about our origins and identity. The emerging picture suggests that we share a profound connection with our extinct cousins, deeper than previously imagined.
NEANDERTHALS WITHIN US
Until recently, the influence of ancient human genetics remained hidden, as scientists relied on bone shapes and sizes for insights. However, breakthroughs in studying ancient DNA, pioneered by Nobel laureate Svante Pääbo, have unveiled a wealth of information.
These advances allow scientists to observe genetic changes over time, driven by environmental adaptation or random mutations. They can also determine the extent of ancient DNA in modern populations. For instance, some African groups have minimal Neanderthal DNA, while those of European or Asian descent possess 1% to 2%. In Melanesia, spanning from New Guinea to Fiji, Denisovan DNA accounts for 4% to 6% of the population’s genetic makeup.
This seemingly small genetic contribution accumulates in modern humans. Roughly half of the Neanderthal genome persists in scattered fragments within our DNA.
The impact of this ancient DNA is multifaceted. It has been linked to both beneficial and detrimental effects. For instance, Neanderthal DNA conferred immunity advantages when Homo sapiens migrated out of Africa into Eurasia. However, this legacy may also lead to overactive immune responses, causing autoimmune diseases.
Similarly, genes inherited from Neanderthals, such as those associated with blood clotting, might have been advantageous in ancient times but can now elevate the risk of health issues, like strokes.
In a striking revelation, a significant genetic risk factor for severe COVID-19 was traced back to Neanderthals, highlighting how ancient DNA can influence contemporary health outcomes. Conversely, other Neanderthal DNA variants offer protection against severe COVID-19.
The list of Neanderthal genetic connections continues to grow, encompassing traits like skin color, hair color, behavior, skull shape, and susceptibility to Type 2 diabetes. Some individuals carry Neanderthal pain receptors, making them more sensitive to pain, while others inherit a Neanderthal receptor associated with fertility and fewer miscarriages.
Denisovan genetic legacy is less understood, but it has been associated with benefits like improved fat metabolism and adaptation to high altitudes, particularly in Tibetans.
Remarkably, scientists have also detected signs of “ghost populations” within modern humans’ genetic code, hinting at undiscovered ancient human groups that contributed to our genetic diversity.
SO WHY DID WE SURVIVE?
The traditional narrative of human survival, portraying Homo sapiens as triumphant heroes, no longer holds true, as explained by Potts. Neanderthals and Denisovans had already thrived for millennia by the time our ancestors left Africa. Contrary to past assumptions that we prevailed due to superior behavior and technology, recent research reveals their sophistication. Neanderthals exhibited traits like communication, fire-based cooking, artistic creations, advanced tools, hunting strategies, and even the use of cosmetics and jewelry.
A key factor in our survival appears to be our capacity for extensive migration. As Zeberg notes, we dispersed globally, surpassing other human forms in this regard. While Neanderthals were well-suited for cold climates, Homo sapiens demonstrated adaptability to diverse environments after originating in tropical Africa, making us culturally versatile for various regions worldwide.
In contrast, Neanderthals and Denisovans faced severe challenges in the north, contending with repeated ice ages and geographical constraints that likely limited their populations. Their stocky build required more calories to sustain, making survival and mobility challenging when food was scarce.
An intriguing hypothesis proposed by anthropologist Pat Shipman, shared by Janet Young, suggests that dogs played a significant role in our survival. Evidence of domesticated dog skulls found in Homo sapiens sites points to early collaboration in hunting, enhancing our ability to secure food.
Around 30,000 years ago, all other hominin species had vanished, leaving Homo sapiens as the sole survivors of the human family tree.
‘INTERACTION AND MIXTURE’
With each new scientific revelation, our debt to our ancient cousins becomes increasingly apparent. The story of human evolution isn’t simply one of survival and extinction, as John Hawks emphasizes, but a narrative of interaction and intermingling.
As science advances further, researchers anticipate uncovering more insights. They can now extract information from the tiniest remnants of ancient lives, including DNA extracted from soil and sediment in the locations where our distant relatives once resided.
There are still uncharted territories across the globe that hold the promise of further discoveries. Hugo Zeberg suggests the establishment of “biobanks” in more countries, collecting biological samples for future exploration.
As scientists delve deeper into the genetic legacy of humanity, they anticipate unearthing additional evidence of our intricate mingling with ancient cousins and the lasting contributions they made to our genetic makeup. Perhaps, as Zeberg suggests, it’s time to view them not as so fundamentally different from us, but as integral threads in the complex tapestry of our shared human story.