Horsrshoe crabs - No Evolution over millions of years

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Intrinsically disordered proteins (IDPs) are proteins that lack a stable three-dimensional structure under physiological conditions. As such they are not under natural selection which according to theory acts on structured proteins. Instead, IDPs exist as a dynamic ensemble of conformations. IDPs are often involved in signaling and regulation, where their flexibility allows them to interact with multiple partners.

Horseshoe crabs are a very ancient group of animals, with a fossil record that dates back over 450 million years. They have not changed over time, and are often described as living fossils.

Other species with extreme evolutionary age include Coelacanths,Tardigrades,& Medusa jellyfish to name a few.

One possible explanation for the evolutionary "stasis" of horseshoe crabs is that their IDPs play a role in maintaining their stability. IDPs are often able to interact with multiple partners in different ways, which can give them a high degree of adaptability without evolution. This may have been particularly important for horseshoe crabs in the early stages of their development ,when they were facing new challenges and adapting to new environments. 

IDPs play an important role in the horseshoe crab's immune system and other physiological processes. The unique properties of IDPs may have helped horseshoe crabs to adapt to new environments and survive over millions of years without Darwinian evolution.


IDPs are also thought to be far more resistant to mutations than folded structured proteins. This is because IDPs do not have a specific three-dimensional structure, so mutations are much less likely to disrupt their function. IDP have intrinsically disordered regions (IDR) which have simple repetitive amino acids that provide flexibility. They are not the active binding sites therefore a mutation in these regions can be tolerated over millions of years. 

Overall, the increased presence of IDPs in horseshoe crabs is a possible explanation for their evolutionary stasis. The percentage of proteins of horseshoe crabs that are intrinsic disordered proteins (IDPs) is estimated to be around 40%. This is higher than the percentage of IDPs in other eukaryotes. The high percentage of IDPs in horseshoe crabs may be due to their unique lifestyle and exposure to a larger microbiome or waterborne microbes. Horseshoe crabs are marine invertebrates that have survived for over 450 million years. They live in harsh environments, such as tidal flats and estuaries, where they are exposed to a wide range of stresses, such as salinity changes, temperature fluctuations, and predators. The microbiome they are exposed to have adapted to these extreme environments and can transfer this adaptation to the horseshoe crabs over deep time.

The horseshoe crab (Limulus polyphemus) has approximately 1.2 billion base pairs of noncoding (Junk) DNA, which makes up about 97% of its total genome. This is significantly more noncoding DNA than with most organisms.

As microbiome TEs and IDP are not under natural selection they can accumulate over time. Horseshoe crabs have been around for over 450 million years, and their genome has had a long time to accumulate TEs.

The high amount of TEs in horseshoe crabs suggests that it may be playing an important role in their biology. 

Exposure to larger numbers of adaptive microbiomes can cause increased horizontal gene transfer (HGT) of transposable elements (TEs) and intrinsically disordered proteins (IDPs), which can increase the age of a species.


Microbiomes are the bacteria in the area and the GI tract and skin. Watery environments have larger numbers of microbiomes. Microbiomes carry TEs that can move around the genome and insert themselves into new locations by HGT. Microbes are a major source of genetic diversity in the environment. When an organism is exposed to a large number of microbes, it is more likely to encounter TEs and IDPs that it has never seen before. This can lead to the accumulation of TEs and IDPs in the organism's genome.

The accumulation of TEs and IDPs can have a number of effects on an organism, including:

  • Increased "biased" (not random) mutations (GC>AT & AT>GC) rates: TEs can cause biased mutations by inserting themselves into genes increasing gene expression. As well, TE retrotransposons affect DNA repair and recombination affecting AT>GC conversions (BGC). IDPs can also cause mutations by interacting with DNA repair proteins.

  • Increased rates of speciation: The accumulation of TEs and IDPs can lead to the formation of new species by creating genetic barriers between populations.

Over time, the accumulation of TEs and IDPs can lead to an increase in the age of a species. This is because TEs and IDPs can accumulate over time without being removed by natural selection. As a result, older species are more likely to have a higher number of TEs and IDPs in their genomes than younger species.

The effects of HGT on the age of a species are complex and depend on a number of factors, including the type of TEs and IDPs that are transferred, the frequency of HGT, and the fitness effects of the transferred genes. However, there is growing evidence that HGT play a significant role in the development and adaptation of new species and the aging of existing species.

Horizontal gene transfer (HGT) prefers transposable elements (TEs) with a greater percentage of intrinsically disordered proteins (IDPs). 

TEs with a higher percentage of IDPs are more likely to be transferred between bacteria. Scientists  found that IDPs were more likely to be found at the boundaries of TEs, suggesting that they play a role in the packaging and mobilization of TEs.

Overall, the evidence suggests that IDPs play an important role in HGT. This is likely due to their ability to bind to other proteins and nucleic acids, which makes them well-suited for mediating the transfer of genetic material between different organisms without NeoDarwinian mechanisms.

Here are some possible reasons why HGT prefers TEs with a greater percentage of IDPs:

  • IDPs are more likely to be found at the boundaries of TEs, which suggests that they play a role in the packaging and mobilization of TEs.

  • IDPs are more likely to be involved in protein-protein interactions, which is necessary for TEs to interact with other proteins and nucleic acids during HGT.

  • IDPs are more flexible and adaptable than proteins with well-defined three-dimensional structures, which may make them better suited for mediating HGT in a variety of different environments.

In summary NonDarwinian IDPs and microbiome HGT of TEs in Horseshoe crabs can cause evolutionary status or no evolution over millions of years without Darwin.

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