Earthworms’ Genomes Broke The Rules of Evolution And Could Prove Charles Darwin Wrong, Claims Study

Analysis of DNA from earthworms has challenged the theory proposed by Charles Darwin. The theory dictates that creatures will go through small changes over time to enter their next evolutionary stage, according to Earth. Even at the time of the proposal, many raised questions about this aspect of the theory, claiming that these "small changes" are not reflected in the fossil record. However, Darwin argued that these "changes" were lost or had not been found. A new study indicates that evolution, at least in earthworms, was not composed of small changes. The study was published in Nature Ecology & Evolution.

Insights from Earthworm's DNA

For the study, researchers sequenced high-quality genomes of several earthworm species. They then compared these genomes to the genomes of other annelids, such as leeches and bristle worms. The genome database, formulated through this process, allowed experts to look back 200 million years into the history of these invertebrates. They were ecstatic to get insights about that particular timeframe because, as per past investigations, invertebrates like worms began to transition onto land during that period. It implies that certain features in worms must have transformed to fit in with the new habitat. According to Darwin's theory, the transformation should have been facilitated by several "small changes" across several millennia in the form of possible intermediate species. The results did not showcase this at all.

The transformation in the database was not slow or spread across a long time; instead, it was instantaneous. The worms exhibited "punctuated equilibrium," proposed by scientists Stephen Jay Gould and Niles Eldredge in 1972, claiming that species remain the same for many years, and change suddenly in response to a change in circumstances or other reasons. The evolution trajectory noted in earthworms followed this idea. The genomes "shattered," possibly in response to the sudden alteration of living space, and then reassembled to adapt. "The entire genome of the marine worms was broken down and then reorganized in a completely random way, in a very short period on the evolutionary scale," said Rosa Fernández, the lead researcher of the IBE’s Metazoa Phylogenomics and Genome Evolution Lab. "I made my team repeat the analysis again and again because I just couldn’t believe it."

Reason behind the Drastic Deconstructions' Success

The genome breakdown succeeded due to the presence of chromosomes in the DNA, according to Science Daily. These chromosomes are much more flexible than their counterparts in vertebrates and other model organisms. This flexibility allowed the chromosomes to take different spots in the genome's 3D structure amid rearrangement and yet survive. The change in habitat possibly triggered the genes to get reorganized so the worm could fulfill crucial functions like breathing air. The database also showed that not only were the genes rearranged, but some of the gene fragments that had been separated were also linked during the breakdown. This rearranged structure is called "genetic chimeras," which also impacted evolution. Before this examination, researchers believed that such chaos typically results in the extinction of species, but this analysis showcases that the rearrangement could also aid beings in surviving the drastic changes around them. 

Doubt Over Genome Stability

The results of this examination cast serious doubts over the necessity of genome stability. According to past studies, genes should be in a specific location across all species to maintain stability during evolution. Considering that earthworms still thrive on Earth, the assertion is possibly incorrect. "In fact, stability could be the exception and not the rule in animals, which could benefit from a more fluid genome," Fernández added.

Researchers want to look more into such unique evolutionary trajectories. Further investigation could shed light on the reason why such a rearrangement results in thriving for invertebrates like worms but not for humans, where it has been connected to cancers. The contrast could provide more meaningful insights about genomes in the animal kingdom.