An international team of more than 100 scientists has undertaken a most complex and challenging task: they’ve determined the timings and patterns of evolution for most of the insect family tree, until they arrived at at the original insect foremother which lived some 500 million years ago. Thus, the researchers were able to pinpoint when the major insect groups, most still alive today, first surfaced on the world or when the first flying insects spread their wings.

The insect family tree

Studying ancient insects is no easy task. Because they’re so tiny and squishy, there’s little fossil evidence to lie around. Their sheer monstrous diversity both helps and doesn’t at the same time. Roughly 80% of the more than 1,6 million species of animals described by scientists today are insects or one out of two multicellular organisms (including plants). Really, there’s no mistake – insects rule the world now and will continue to do so for a long, long time. We like to think us humans are really smart, but it’s worth considering that the last human carcass will be consumed by insects; true story. But for how long exactly have insects reigned the world?

The Australian Emperor Dragonfly is only a handful compared to its ancestors who measured more than 60cm. Flickr/Daniel lightscaper, CC BY

The answer to this highly challenging question was attempted by a team made out of some of the world’s most renowned biologists, taxonomists, geneticists and mathematicians, as part of the 1000 Insect Transcriptome Evolution project. To this end, the researchers  used a DNA sequence dataset of unprecedented scale and new analysis techniques, in conjunction of course with fossil records.

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Genetics was very important for this kind of project, because genes can act as a sort of molecular clock. By looking at the genes of various insects, scientists can infer when they diverged based on what genes they share. Some 140 types of insects – such as moths, flies, wasps and beetles – had their DNA sequenced, meaning thousands of samples for thousands of species.

The Snakefly (Dichrostigma flavipes) didn’t give up limbs to evolve wings. Credit: Dr. Oliver Niehuis, ZFMK, Bonn

Checking the molecular clock

To use the molecular clock, the scientists had to look at genes that were common among species and some 1,478 directly comparable genes for the analyses were eventually selected. The possible gene combinations, however, were in the order of million trillions. There’s no supercomputer that can crunch these numbers, but luckily the team was large and broad in fields of expertise. This is where computer scientist and bioinformatics expert Alexandros Stamatatakis came in and he developed a mathematical method to exclude highly unlikely combinations, and focus on likely ones.

Evolutionary biologist Karl Kjer of Rutgers University in New Jersey, one of the study leaders said, “The Earth 480 million years ago looked more like Mars than our Earth today: nothing but rock, with no life on land. The oceans were full of life, but life out of the water is really quite challenging. Plants and insects co-evolved simultaneously, each shaping the other.”

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The Cuckoo wasp (Hedychrum nobile) – one of the insects whose DNA was sequenced for the study. Credit: Dr. Oliver Niehuis, ZFMK, Bonn

Their work reveals that insects first emerges around the time plants appeared on the planet as well, some 500 million years ago, during the Early Ordovician Period. The ancient ancestors of insects  (Hexapoda) were probably similar to silverfish, modern primitive insects that have never evolved wings. Speaking of wings, insect flight emerged some 406 million years ago, around the same time plants began to really diversify on land and grow taller. Also, very important to note, is that insect diversification took off well before Angiosperms (flowering plants).  The scientists say that the first insects probably evolved from a group of venomous crustaceans called remipedia.

Silverfish (Lepisma saccharina). Flickr/Stanislav Sedov, CC BY

Notice that insects adapted extremely fast, and it’s not hard to understand why. Insects reach maturity extremely fast and breed by the swarms. It’s a lot more likely for a helpful mutation to surface and stick in a large population. Most major groups of insects appeared in a burst of evolution about 350 million years ago such as grasshoppers and cockroaches. Many common groups of insects such as flies, wasps and beetles appeared more than 200 million years ago.

The study published in Science offers the most detailed and extensive analysis of its kind. Now, scientists will have this massive database at their disposal to study how insects survived and adapted to some of the direst crisis in the planet’s history.