The classic explanation is that elaborate and complex structures must exist because they confer some functional benefit to the organism, so natural selection drives states of increasing complexity.
Clearly, in some cases complexity is adaptive, such as the evolution of the eye (complex eyes see better than simple ones). But at the molecular level, a new study has found that there are other simple mechanisms that drive the accumulation of complexity.
Complexity
He new study, conducted by researchers at the University of Chicago, suggests that elaborate protein structures accumulate over time, even when they serve no purpose, because a universal biochemical property and the genetic code force natural selection to conserve them.
Most of the proteins in our cells form specific complexes with other proteins, a process called multimerization. Many proteins, especially those with high molecular weights, have a quaternary structure, this means that they are made up of several polypeptide chains (from two to hundreds of them). Each of these chains is called a subunit, and the union of several subunits is what we have called a multimer, or multisubunit protein.
Multimer. This protein is a multimer formed by three polypeptide chains (protein subunits), therefore it is a trimer.
Like other types of complexity in biology, multimers are often thought to persist over evolutionary time because they confer some functional benefit favored by natural selection.
To prove it, the study analyzed the evolution of multimerization in a family of proteins called steroid hormone receptors, which assemble in pairs (called dimers). To do this, they used a technique called ancestral protein reconstruction, which allowed them to recreate ancient proteins in the laboratory and experimentally examine how they were affected by mutations that occurred hundreds of millions of years ago.
To their surprise, they found that the ancient proteins did not function any differently when assembled into a dimer than if they had never evolved to dimerize. There was nothing useful or beneficial in the formation of the complex. The explanation for why the dimeric form of the receptor has persisted for 450 million years turned out to be surprisingly simple, he explains. Georg Hochberg, one of the authors of the study:
These proteins gradually became addicted to their interaction, although there is nothing useful about them. The parts of the protein that form the interface where partners bind accumulated mutations that were tolerable after dimer evolution, but that would have been deleterious in the alone state. This made the protein completely dependent on the dimeric form, and it could no longer go back. Useless complexity took hold, essentially forever.
The researchers suggest, then, that simple biochemical, genetic and evolutionary principles make the entrenchment of molecular complexes inevitable. This mechanism, which operates on thousands of proteins for hundreds of millions of years, could drive the gradual accumulation of many useless complexes inside cells.
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The news
Natural selection seems to preserve the complex even if it has no specific usefulness
was originally published in
Xataka Science
by
Sergio Parra
.