Genomic Giants: The Lungfish That Rewrote DNA Records

Nature delivered a stunning surprise in 2024 when scientists unveiled the genomic champion of the animal kingdom. The South American lungfish, Lepidosiren paradoxa, carries a DNA blueprint containing 91 billion chemical letters—30 times larger than the human genome. This ancient air-breathing fish has accumulated genetic material at a staggering rate, adding the equivalent of an entire human genome every 10 million years over the past 100 million years.

What makes this discovery particularly fascinating is that despite harboring this enormous genetic library, the lungfish contains roughly the same number of protein-coding genes as humans—approximately 20,000. The remaining 90% of its genome consists of repetitive DNA sequences called transposable elements, or “jumping genes,” that have run rampant throughout the species’ evolutionary history. These parasitic genetic elements copy themselves and insert new copies randomly throughout the genome, creating an ever-expanding molecular landscape that challenges our understanding of genomic organization.

The mechanism behind this unprecedented expansion involves the breakdown of cellular quality control systems. Unlike other vertebrates that maintain molecular brakes on transposable element activity through piRNA pathways and specialized protein networks, lungfishes have lost key regulatory genes. This evolutionary oversight has allowed transposable elements to proliferate unchecked, transforming the lungfish genome into a repetitive DNA warehouse. Remarkably, evidence suggests these elements remain active today, meaning the genome continues its relentless expansion.

This genomic gigantism carries profound biological costs. Each of the lungfish’s 19 chromosomes rivals the size of the entire human genome, requiring enormous cellular energy to replicate and maintain. The nuclei housing this massive DNA must expand to accommodate the genetic cargo, and cell division becomes a marathon of molecular machinery working overtime. Yet somehow, these ancient fish have survived for hundreds of millions of years with their bloated genomes, representing one of evolution’s most extreme experiments in genetic excess.

The lungfish genome offers unique insights into vertebrate evolution. As the closest living relatives to the first land animals, lungfishes serve as molecular time capsules preserving genetic information about the epic transition from water to land 370 million years ago. By comparing the genomes of South American, African, and Australian lungfish species, researchers have traced how limb-like fins evolved and sometimes disappeared, providing clues about the developmental toolkit that enabled vertebrates to colonize terrestrial environments.