Darwin’s theory of evolution

 This small ground beetle is rekindling debate on Darwin’s theory of evolution

When a mass extinction event 66 million years ago wiped out three-quarters of the world’s plants and animals – including the dinosaurs – among the survivors was a tiny, black beetle.

The Cretaceous-Paleogene extinction event triggered one of the most profound restructurings of Earth’s natural environment, and those species that survived had to change and evolve as they adapted to the new world order, following Charles Darwin’s theory of evolution.

But that tiny beetle could be turning Darwin’s theory on its head. According to two recent studies conducted by several Chinese researchers and their international collaborators, this common insect has remained unchanged for at least 100 million years.

In fact, it is in a state the researchers call “evolutionary stasis”.

The studies, published in Palaeoentomology and The Innovation in April and May respectively, were led by Cai Chenyang, a researcher at the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences in southern China’s Jiangsu province.

Scientists found a preserved Cretaceous species of Loricera, a genus of ground beetles, in three amber fossils from the Hukawng Valley in northern Myanmar dated to around 100 million years ago.

Widespread in the northern hemisphere, these beetles are found in damp soil and feed mainly on springtails. Comparing the preserved specimens with their modern day counterparts, the researchers found that the insect had not changed its shape, size or even feeding habits, despite drastic changes in its living environment, including the mass extinction event.

For example, the basal segments of the antennae of extant adult Loricera species bear long, strong setae, or bristles. Rapid closure of the segments of the antennae traps prey in a “cage” of setae, effectively reducing the ability of trapped springtails to escape by jumping. They found that this “setal trap” in the fossils was almost identical to that of living adults.

Robert Shedinger, a professor of religion at Luther College in Iowa, USA, who was not involved in the research, said this could challenge Darwin’s theory. “Over 100 million years, one would expect changing selection pressures to lead to changes in biological structures. But this is not always the case, as we see with this beetle,” he said.

Shedinger, who wrote the book Darwin’s Bluff: The Mystery of the Book Darwin Never Finished, said evolutionary stasis was actually a fairly common occurrence in the fossil record and, in his view, “presents something of a challenge to Darwinian evolution”.

But Cai said the team’s findings could not overthrow Darwin’s theory, as these beetles might not have undergone significant natural selection.

He said that when the natural environment changed significantly, strictly herbivorous or strictly carnivorous animals, such as dinosaurs, were more likely to be affected. In contrast, smaller creatures were typically more adaptable to unfavourable environments.  Their paper that appeared in The Innovation speculated that the beetle’s long-term stasis may have been due in part to the high abundance of springtails, which “would serve as a reliable food source through geological history”.

“When people think of Darwinian evolution, they often envision organisms continuously evolving and changing. However, Darwin’s scientific framework also acknowledged the possibility of evolutionary stasis, which he referred to as ‘living fossils’,” Cai said.

It is widely accepted by the scientific community that the impact of a large asteroid – 100 times the size of the International Space Station – on Earth may have triggered the mass extinction event some 66 million years ago. That impact would have ejected a huge amount of rock debris into the atmosphere, covering the Earth and obscuring the sun. With no sunlight able to penetrate this global dust cloud, photosynthesis would have ceased, resulting in the death of green plants and the disruption of the food chain.

For species to survive, they would have had to adapt.

That is what Charles Darwin proposed in his 1859 theory of evolution in the book, On the Origin of Species. His idea of “natural selection” suggested that organisms that are better adapted to their environment are more likely to survive – a process that causes species to evolve over time as the environment around them changes.

But there are some creatures such as crocodiles that somehow bypassed the forces of natural selection, evolving very little from their prehistoric ancestors. Another example is an ancient group of ray-finned fish known as gars. They are only minimally different from the same species in the fossil record from 100 million years ago.

In a paper published in May in the journal Evolution, researchers from Yale University and other US institutions found that the reason garfish have remained unchanged for millions of years could be due to their slow rate of molecular evolution. A growing number of scientists have been calling for a reassessment of Darwin’s theory in recent years. In 2014, in an article published in the journal Nature, eight scientists posed the question, “Does evolutionary theory need a rethink?” Their answer? “Yes, urgently.”

They pointed out that without an extended evolutionary framework, the theory neglects key processes. Religion professor Shedinger said: “Modern evolutionary theory is a far more sophisticated theory than that proposed by Darwin, but it is still very much based on a Darwinian foundation and is accepted by most mainstream biologists.

“But there are a number of critics both within and outside the biological establishment.”

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