Featured Research

from universities, journals, and other organizations

Flexibility Trumps Fitness In Sexual Reproduction, Says New Theory In Evolutionary Biology

Date:
December 3, 2008
Source:
University of California - Berkeley
Summary:
An intriguing new theory of evolutionary biology says the reason sexual reproduction may be so successful is that it promotes genes that work well in combination with many other genes. This idea of genetic mixability hits on the difficulty evolutionary biologists have had in understanding sex, specifically its role in population genetics and natural selection.

New research suggests that the utility of sex may be its ability to promote genes that play well with many other partners.
Credit: iStockphoto/Grant Dougall

The utility of sex, according to an intriguing new theory of evolutionary biology, may be its ability to promote genes that play well with many other partners rather than those that shine with just one specific set of genes.

This idea of genetic mixability, described in the journal Proceedings of the National Academy of Sciences the week of Nov. 24, hits on the difficulty evolutionary biologists have had in understanding sex, specifically its role in population genetics and Darwin's survival-of-the-fittest mantra.

"It's the generalist winning over the specialist," said Christos Papadimitriou, professor of computer sciences at the University of California, Berkeley, and co-author of the paper.

"During the past century, it has often been assumed that sexual reproduction should somehow facilitate the increase in fitness under natural selection, leading to the 'best' combinations of genes," said lead author Adi Livnat, a Miller Institute post-doctoral fellow based at UC Berkeley's Department of Electrical Engineering and Computer Sciences. "But no agreement has been reached on whether and how this could really work. One might think, for example, that by bringing together genes from different individuals, sexual reproduction could create a very successful combination of genes. But just as sexual reproduction will create that very successful combination of genes, it could also break it down in the next generation."

That sex can actually impede the increase in the fitness of the population raises the question of how it can remain the dominant form of reproduction across all manner of species. Sex - at its core the merging of genes from different individuals to create genetically unique offspring - is the reproductive method of choice from humans to plants to many fungi. This form of reproduction must be doing something right, in terms of evolution.

Veering from the assumption that sexual reproduction increases the average fitness of a population, the researchers came up with a new measure they call "mixability" to represent a gene's ability to perform well across many different combinations. They tested the mixability measure in a number of scenarios within a well-established population-genetic framework.

They found that if the goal is to maximize fitness by finding a particularly good combination of genes, asexual reproduction - which increases a population's numbers at a much faster rate than sexual reproduction - works very well.

In contrast, sexual reproduction, through the process of recombination and segregation of chromosomes, strongly favors genes that work well in many different variations rather than any one good combination. In that view, the authors wrote, alleles of the same gene compete with each other based upon how well they perform on average rather than how well they perform in any one specific combination.

"It's important to note that during the process of evolution, the mixability value increases, though it doesn't increase all the time," said the paper's co-author Marcus Feldman, professor of biology at Stanford University and a world-renowned theorist in evolutionary biology. "The approach we take is different from usual because we're interested in evolutionary transience, and in the long run, our mixability value may actually decrease because too much variability is lost from the population."

Even so, sexual reproduction has a great advantage for mixability compared with asexual reproduction, according to the models in the paper.

In what may appear at first to be an unconventional comparison, sexual reproduction has something in common with the rebalancing of a stock portfolio at regular intervals, explained Livnat.

"If every year some money is taken out from stocks that have performed well and reallocated to stocks that lost money, the growth rate of the portfolio is averaged out over time," he said. "Analogously, sexual reproduction entails moving genes from one combination to another in a manner that, over the course of multiple generations, can tie the success of a gene to its average performance across genotypes rather than its maximum performance."

Livnat started thinking about this problem in discussions with Papadimitriou, a leading computer theorist whose research includes optimization algorithms. Such programs are widely used to find best outcomes in applications such as computer networks, transportation planning and financial models.

The researchers explained that of the two main techniques for optimization programming, one, known as simulated annealing, solves problems using a process analogous to asexual reproduction, while the other, known as genetic algorithms, is inspired by sexual reproduction. Genetic algorithms should theoretically be the better of the two techniques at finding the best solutions for a problem because they mimic an approach that is so dominant in nature. However, as it turns out, genetic algorithms often perform no better than simulated annealing.

"We were trying to figure out why an algorithm that mimics a good idea in nature was not coming up with better results," said Papadimitriou. "It dawned on us that what sexual reproduction is doing is not maximizing fitness, but doing something more subtle. It is bringing about genetic variants that perform well across many possibilities in connection with a great variety of genetic partners. If a particular gene variant can do well with many other alleles, not just a highly specialized variant, evolution is advanced."

The researchers noted that when the human genome was sequenced in 2003, there was some surprise that humans did not possess far more genes than other species. It turns out that how those genes are combined may be a critical factor in distinguishing humans from other species, supporting the importance of flexibility over fitness.

Feldman, who has studied the evolution of sex and recombination for more than three decades, said he expects this new theory to trigger much debate among his peers. "This problem of understanding sex will go on being one of the central issues in evolution," he said.

The Miller Institute for Basic Research in Science, National Science Foundation, the National Science and Engineering Research Council of Canada and the National Institutes of Health helped support this work.


Story Source:

The above story is based on materials provided by University of California - Berkeley. Note: Materials may be edited for content and length.


Cite This Page:

University of California - Berkeley. "Flexibility Trumps Fitness In Sexual Reproduction, Says New Theory In Evolutionary Biology." ScienceDaily. ScienceDaily, 3 December 2008. <www.sciencedaily.com/releases/2008/11/081124174903.htm>.
University of California - Berkeley. (2008, December 3). Flexibility Trumps Fitness In Sexual Reproduction, Says New Theory In Evolutionary Biology. ScienceDaily. Retrieved October 23, 2014 from www.sciencedaily.com/releases/2008/11/081124174903.htm
University of California - Berkeley. "Flexibility Trumps Fitness In Sexual Reproduction, Says New Theory In Evolutionary Biology." ScienceDaily. www.sciencedaily.com/releases/2008/11/081124174903.htm (accessed October 23, 2014).

Share This



More Plants & Animals News

Thursday, October 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Working Mother DIY: Pumpkin Pom-Pom

Working Mother DIY: Pumpkin Pom-Pom

Working Mother (Oct. 22, 2014) How to make a pumpkin pom-pom. Video provided by Working Mother
Powered by NewsLook.com
Goofy Dinosaur Blends Barney and Jar Jar Binks

Goofy Dinosaur Blends Barney and Jar Jar Binks

AP (Oct. 22, 2014) A collection of dinosaur bones reveal a creature that is far more weird and goofy-looking than scientists originally thought when they found just the arm bones nearly 50 years ago, according to a new report in the journal Nature. (Oct. 22) Video provided by AP
Powered by NewsLook.com
San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

Reuters - Light News Video Online (Oct. 22, 2014) The pair of rare white northern rhinos bring hope for their species as only six remain in the world. Elly Park reports. Video provided by Reuters
Powered by NewsLook.com
Raw: Bear Cub Strolls Through Oregon Drug Store

Raw: Bear Cub Strolls Through Oregon Drug Store

AP (Oct. 22, 2014) Shoppers at an Oregon drug store were surprised by a bear cub scurrying down the aisles this past weekend. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins