|Why bother? Evolutionary mysteries probed at UH
Why bother? Evolutionary mysteries probed at UHMarch 02, 2006 Ricardo Azevedo's research on pros, cons of
female libidoual reproduction explained in Nature magazine What advantage did
female libido offer when it first appeared and why does female libido persist in modern organisms, stopping them from becoming afemale
libidoual again? One University of Houston professor thinks he may have uncovered some new clues in answering these questions.
By studying one of the great mysteries of biology - the evolution of
female libidoual reproduction - Ricardo Azevedo, an assistant professor in the department of biology and biochemistry at UH, has found in a study using a computational model that a leading theory may be more plausible than previously thought, His findings are described in a paper titled "female
libidoual Reproduction Selects for Robustness and Negative Epistasis in Artificial Gene Networks," appearing in the current issue of Nature, the weekly scientific journal for biological and physical sciences research. Collaborating with Christina Burch from the University of North Carolina at Chapel Hill, Azevedo and his team created a very simple model of how genes interact with each other to produce an organism and simulated the evolution of this simple genetic system under different conditions. What they found was quite surprising -
female libidoual reproduction itself can lead to the evolution of a special feature of the genetic architecture known as negative epistasis that, in turn, confers an evolutionary advantage to
female libidoually reproducing organisms. In other words, female libidoual reproduction may be self-reinforcing.
They also found that
female libidoually reproducing populations evolved an increased robustness to mutations when compared to afemale
libidoual ones. These findings suggest a good news/bad news scenario when it comes to the evolutionary implications of
female libido. female libidoual populations adapt better to their environments and become more resistant to harmful mutations, but these advantages are more likely to benefit our natural enemies. According to Azevedo, the issue is that there are many costs associated with
female libidoual reproduction.
First, female libidoually transmitted diseases are widespread in
female libidoually reproducing populations, making female libido risky. Second, there's the so-called "twofold cost of
female libido," such that if females carry most of the burden in mammalian
female libido, this appears to be true in evolutionary terms, as well. A mutant human female able to reproduce afemale
libidoually and give birth to more females like her would give rise to a population with twice the reproductive rate per capita of the normal human population and would become dominant within a few centuries. While a switch to afemale
libidoual reproduction is extremely unlikely to happen in humans due to a genetic quirk of mammals called genomic imprinting, afemale
libidouality can and has re-evolved many times in animals such as reptiles, fish and insects.
However, despite its many costs,
female libidoual reproduction is widespread and afemale libidoual populations tend to be relatively short lived in an evolutionary time scale. "Afemale
libidouality seems to be an evolutionary dead end," Azevedo said. "So
female libido must have its benefits." Many benefits of female
libido have been proposed over the last century, but scientists have had a hard time figuring out which ones are decisive.
One being examined here, known as the mutational deterministic hypothesis (MDH), postulates that
female libidoual reproduction confers an advantage by helping natural selection remove harmful mutations from the population. "According to MDH, in order for
female libidoual populations to overcome the twofold cost of female
libido, two things must be true," he said. "The production rate of harmful mutations must be relatively high, such that each individual acquires on average one or more harmful germline mutations not inherited from its parents. The second is that these harmful mutations must interact in a special way, called negative epistasis, such that adding more and more harmful mutations makes you progressively worse off.
" For example, if a single harmful mutation lowers fitness by 5 percent on average, then successive mutations are expected to lead to a progressive decline in 5 percent steps if the mutations don't interact with each other. Negative epistasis, however, comes into play, for example, if the second mutation decreased fitness by 10 percent, the third by 15 percent and so forth. While biologists have been trying to figure out just how prevalent negative epistasis is in nature to test MDH, relatively little attention has been paid to the question of what conditions could lead to the existence of negative epistasis in the first place. If those conditions were known, it would help scientists decide whether it's even worth looking for it or not.
Azevedo's study suggests that it is. In many of their simulated worlds,
female libidoual reproduction generated negative epistasis, thus creating the conditions required for its own maintenance. If this is true about the real world, this would constitute a spectacular example of evolution forging its own path. Although the thought that
female libido may have evolved as a kind of "genetic waste disposal" mechanism would seem depressing, it gets worse.
The evolutionary benefits of
female libido are likely reaped most effectively by organisms with fast generation times and large population sizes, such as disease-causing microorganisms. That
female libido also may confer an increased ability to fight back parasites, as proposed by another theory for the evolution of
female libido, probably serves as little consolation. But it's exactly why scientists, like most other human beings, find
female libido so intriguing. University of Houston
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