How Fossilized Remnants Shape Your Health and Biology
Deep within your DNA, a forgotten history of viral invasions is shaping your life in ways science is just beginning to understand.
Imagine discovering that your genetic blueprint, the very code that makes you human, is partially composed of ancient viral DNA. These are not active infections, but rather fossilized remnants of viruses that infected our primate ancestors millions of years ago. Once dismissed as mere "junk DNA," these viral leftovers are now revealing themselves as surprising players in human development, disease, and evolution. Welcome to the hidden world of endogenous viral elements (EVEs)—the ancient viruses that became permanent residents in our genome, influencing everything from early development to neurodegenerative diseases.
The human genome is far more than just human. About 8% of our DNA consists of remnants of ancient viruses that embedded themselves into our genetic code over the course of human evolution 6 . When you consider that nearly half of our genome is made up of transposable elements (or "jumping genes") overall, the scale of this viral legacy comes into focus 6 .
These viral sequences got there through a process that began millions of years ago. When our primate ancestors were infected with viruses, some of these pathogens managed to insert their genetic material into the reproductive cells (sperm or egg cells). Instead of causing disease, this viral DNA became a permanent part of the host's genetic inheritance, passed down from generation to generation 6 . These embedded sequences are known as endogenous viral elements (EVEs) .
Approximately 8% of human DNA consists of ancient viral remnants, with nearly half our genome made of transposable elements.
| Type of Element | Description | Potential Biological Role |
|---|---|---|
| HML-2 | The youngest known endogenous viral elements in humans | Linked to prostate cancer, lupus, and other diseases |
| PEG10 | An ancient viral protein left behind by a virus that infected primates 30-50 million years ago | Contributes to amyotrophic lateral sclerosis (ALS) when overactive in nerve tissue 1 |
| MER11 | A group of transposable elements within primate genomes | Plays a role in early human development and gene regulation 6 |
Uncovering the functions of these ancient viral remnants requires sophisticated modern technology. Researchers use an array of specialized tools to identify and characterize these sequences and understand their biological effects.
Determining the complete DNA sequence of an organism to identify and catalog viral remnants within human and primate genomes 6 .
Measuring how actively a gene is being used by a cell to understand when and where viral elements are active during development or in disease 6 .
"The incredible diversity of these viruses, coupled with our lack of knowledge, significantly limits our ability to understand, monitor, control, and potentially benefit from their interactions" within our bodies 2 . The interdisciplinary nature of this research combines biological expertise with advanced computational approaches including artificial intelligence and machine learning to handle the massive datasets involved in virome research 2 .
The relationship between our bodies and these ancient viral sequences is complex, presenting both risks and benefits that scientists are working to unravel.
One of the most significant recent discoveries links an ancient viral remnant to the devastating neurodegenerative disease ALS (amyotrophic lateral sclerosis). Research from CU Boulder has revealed that when an ancient viral protein called PEG10—left behind by a virus that infected our primate ancestors 30-50 million years ago—is present at high levels in nerve tissue, it changes cell behavior in ways that contribute to this fatal disease 1 .
The discovery is particularly important because about half of the human genome is made up of bits of DNA, including proteins, left behind by ancient viruses 1 . Understanding which of these elements might be contributing to disease opens up new therapeutic possibilities.
Despite their potential harms, some ancient viruses have been co-opted by our bodies to serve useful functions. This process represents a remarkable example of turning an invader into an ally.
Research published in Science Advances has identified previously unknown subfamilies of viral elements that play important roles in early human development 6 . One recently integrated sequence, named MER11_G4, was found to have a strong ability to activate gene expression in human stem cells and early-stage neural cells.
This research also suggests that viral transposable elements had a part in shaping human evolution. By tracing how the DNA has changed over time, researchers found that these subfamilies had evolved differently within the genomes of different animals, contributing to the biological differences that distinguish humans, chimpanzees, and macaques 6 .
"Over the course of evolution, some viruses are degenerated or eliminated, some are largely repressed in expression in normal development and physiology, and some are domesticated to serve the human genome. While perceived as solely harmful, some ancient viruses can become part of us, providing raw materials for genome innovation." — Dr. Lin He, molecular biologist at UC Berkeley 6
To understand how scientists connect these ancient viral remnants to modern diseases, let's examine the key experiment linking the PEG10 protein to amyotrophic lateral sclerosis (ALS) in detail.
Researchers noticed that approximately half of the human genome consists of viral remnants, including the PEG10 protein, which originated from a virus that infected our primate ancestors 30-50 million years ago 1 .
Scientists measured PEG10 levels in nerve tissue and observed that this ancient viral protein was present at unusually high levels in contexts associated with ALS 1 .
Researchers examined how elevated PEG10 levels affected nerve cells, observing changes in cellular behavior consistent with the progression of neurodegenerative disease 1 .
The team began working to develop methods to inhibit the rogue PEG10 protein, exploring whether suppressing this ancient viral element could potentially treat or prevent ALS 1 .
The experiments revealed that when the PEG10 protein is overactive in nerve tissue, it triggers changes in cell behavior that contribute to the development and progression of ALS 1 . This finding was significant because it connected an ancient viral element to a modern neurodegenerative disease with no known cure.
The implications are substantial: by targeting these viral remnants, scientists might develop entirely new treatment approaches for conditions that have previously been difficult to treat. Rather than just addressing symptoms, therapies could potentially target the root cause of the disease by quieting these ancient viral sequences.
| Research Finding | Significance | Potential Application |
|---|---|---|
| High PEG10 levels in nerve tissue change cell behavior | Links an ancient viral remnant directly to a modern fatal disease | Provides a new therapeutic target for treating ALS |
| PEG10 originates from a virus that infected primates 30-50 million years ago | Demonstrates the long-term impact of ancient viral infections | Suggests other ancient viruses may contribute to modern diseases |
| Inhibition of PEG10 may be possible | Offers hope for developing effective treatments | Could lead to a new class of therapeutics targeting viral remnants |
"It is early days still, but the hope is this could potentially lead to an entirely new class of potential therapeutics to get at the root cause of ALS" — Alexandra Whiteley, lead researcher 1 .
The study of our inner viral fossils is accelerating rapidly, with several promising directions emerging. The ongoing Human Virome Program, a recently funded NIH initiative, aims to explore the vast array of viruses that live in and on our bodies—collectively known as the virome—and uncover their impact on our health 2 . Unlike traditional approaches that focus on disease-causing viruses, this program takes a broader view by looking at viruses that coexist with us but aren't tied to any known illnesses 2 .
There's growing interest in developing therapies that can target these ancient viral elements. The CU Boulder team working on the PEG10-ALS connection exemplifies this approach, as they're now working to find a way to inhibit the rogue protein 1 .
"To understand the evolution of our genome is one way to understand what makes humans unique," says Dr. Lin He. "It will empower us with tools to understand human biology, human genetic diseases, and human evolution" 6 .
The discovery that our genome contains fossilized remnants of ancient viruses has transformed our understanding of what it means to be human. We are not purely human—rather, we are a complex combination of human and viral elements that have evolved together over millions of years. These viral sequences, once dismissed as genetic junk, are now recognized as important players in our biology, influencing everything from our development to our susceptibility to disease.
As research continues to uncover the roles of these ancient viral remnants, we gain not only insights into human health and disease but also a deeper appreciation for the complex evolutionary journey that has shaped our species. The viruses that infected our ancestors long ago have become an inseparable part of who we are today—quiet passengers in our genome that continue to influence our lives in profound ways.
"Our genome was sequenced long ago, but the function of many of its parts remain unknown. Transposable elements are thought to play important roles in genome evolution, and their significance is expected to become clearer as research continues to advance." — Dr. Fumitaka Inoue of Kyoto University 6