Featured Research

from universities, journals, and other organizations

Inefficient Selection: New Evolutionary Mechanism Accounts For Some Of Human Biological Complexity

Date:
November 4, 2009
Source:
Rice University
Summary:
A painstaking genomic and proteomic analysis has found a new evolutionary mechanism that accounts for some of the biological complexity of human beings. The scientists who found the mechanism say it helps humans cope with the consequences of inefficient natural selection. It fosters complexity by enabling human proteins to become more specialized over time.

Genomic and proteomic analysis has found a new evolutionary mechanism that accounts for some of the biological complexity of human beings.
Credit: iStockphoto/Liang Zhang

A painstaking analysis of thousands of genes and the proteins they encode shows that human beings are biologically complex, at least in part, because of the way humans evolved to cope with redundancies arising from duplicate genes.

"We have found a specific evolutionary mechanism to account for a portion of the intricate biological complexity of our species," said Ariel Fernandez, professor of bioengineering at Rice University. "It is a coping mechanism, a process that enables us to deal with the fitness consequences of inefficient selection. It enables some of our proteins to become more specialized over time, and in turn makes us more complex."

Fernandez is the lead author of a paper slated to appear in the December issue of the journal Genome Research. The research is available online now.

Fernandez said the study drew from previous findings by his own research group and from seminal work of Michael Lynch, Distinguished Professor of Biology at Indiana University and a recently elected a fellow of the National Academy of Science. Lynch's work has shown that natural selection is less efficient in humans as compared with simpler creatures like bacteria. This "selection inefficiency" arises from the smaller population size of humans as compared with unicellular organisms.

"In all organisms, genes get duplicated every so often, for reasons we don't fully understand," Fernandez said. "When working efficiently, natural selection eliminates many of these duplicates, which are called 'paralogs.' In our earlier work, we saw that an unusual number of gene duplicates had survived in the human genome, which makes sense given selection inefficiency in humans."

In prior research on protein structure, Fernandez's team found that some proteins are packaged more poorly than others. Moreover, they found that the least-efficiently packed proteins are structurally stable only when they bind with partner proteins to form complexes.

"These poorly packed proteins are potential troublemakers when gene duplication occurs," Fernandez said. "The paralog encodes more copies of the protein than the body needs. This is called a 'dosage imbalance,' and it can make us sick. For instance, dosage imbalance has been implicated in Alzheimer's and other diseases."

Given selection inefficiency, Fernandez knew that paralogs encoding poorly packed proteins could remain in the human genome for quite a while. So he and graduate student Jianpeng Chen decided to examine whether gene duplicates had remained in the genome long enough for random genetic mutations to affect the paralogs dissimilarly. Fernandez and Chen, now a senior researcher in Beijing, China, cross-analyzed databases on genomics, protein structure, microRNA regulation and protein expression in such troublesome paralogs.

"The longer these duplicate genes stick around due to inefficient selection, the more likely they are to suffer a random mutation," Fernandez said. "Portions of every gene act to regulate protein expression -- by binding with microRNA, for example. We found numerous instances where random mutations had caused paralogs to be expressed dissimilarly, in ways that removed detrimental dosage imbalances."

Lynch said one aspect of Fernandez's research that is potentially groundbreaking is the observed tendency of proteins to evolve a more open structure in complex organisms.

"This observation fits with the general theory that large organisms with relatively small population sizes -- compared to microbes -- are subject to the vagaries of random genetic drift and hence the accumulation of very mildly deleterious mutations," Lynch said.

In principle, he said, the accumulation of such mutations may encourage a slight breakdown in protein stability. This, in turn, opens the door to interactions with other proteins that can return a measure of that lost stability.

"These are the potential roots for the emergence of novel protein-protein interactions, which are the hallmark of evolution in complex, multicellular species," Lynch said. "In other words, the origins of some key aspects of the evolution of complexity may have their origins in completely nonadaptive processes."

Fernandez said the research reveals how increasingly specialized proteins can evolve. He drew an analogy to a business that hires two delivery drivers that initially cover the same parts of town but eventually specialize to deliver only to specific neighborhoods.

"Eventually, even if times become tough, you cannot lay off either of them because they each became so specialized that your company needs them both," he said.

The more simple a creature is, the fewer specialized proteins it possesses. Humans and other higher-order mammals need many specialized proteins to build the specialized tissues in their skin, skeleton and organs. Even more specialized proteins are needed to maintain and regulate them. This complexity requires that the duplicates of the original jack-of-all-trades gene be retained, but this does not happen unless selection is inefficient. This is frequently a point of contention between proponents of evolution and intelligent design.

Fernandez and Chen looked at duplicate genes across the human genome and found that the more poorly packed a protein was, the more likely it was to be distinguished through paralog specialization.

"This supports the case for evolution because it shows that you can drive complexity with random mutations in duplicate genes," Fernandez said. "But this also implies that random drift must prevail over Darwinian selection. In other words, if Darwinian selection were ruthlessly efficient in humans -- as it is in bacteria and unicellular eukaryotes -- then our level of complexity would not be possible."

The research is supported by the National Institutes of Health.


Story Source:

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


Journal Reference:

  1. Ariel Fernαndez, Jianping Chen. Human capacitance to dosage imbalance: Coping with inefficient selection. Genome Research, 2009; DOI: 10.1101/gr.094441.109

Cite This Page:

Rice University. "Inefficient Selection: New Evolutionary Mechanism Accounts For Some Of Human Biological Complexity." ScienceDaily. ScienceDaily, 4 November 2009. <www.sciencedaily.com/releases/2009/11/091103145603.htm>.
Rice University. (2009, November 4). Inefficient Selection: New Evolutionary Mechanism Accounts For Some Of Human Biological Complexity. ScienceDaily. Retrieved April 18, 2014 from www.sciencedaily.com/releases/2009/11/091103145603.htm
Rice University. "Inefficient Selection: New Evolutionary Mechanism Accounts For Some Of Human Biological Complexity." ScienceDaily. www.sciencedaily.com/releases/2009/11/091103145603.htm (accessed April 18, 2014).

Share This



More Fossils & Ruins News

Friday, April 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Couple Finds Love Letters From WWI In Attic

Couple Finds Love Letters From WWI In Attic

Newsy (Apr. 17, 2014) — A couple found love letters from World War I in their attic. They were able to deliver them to relatives of the writer of those letters. Video provided by Newsy
Powered by NewsLook.com
Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

AFP (Apr. 16, 2014) — Explicit Chinese art works dating back centuries go on display in Hong Kong, revealing China's ancient relationship with sex. Video provided by AFP
Powered by NewsLook.com
French Historians Fight to Save Iconic La Samaritaine Buildings

French Historians Fight to Save Iconic La Samaritaine Buildings

AFP (Apr. 15, 2014) — Parisians and local historians are fighting to save one of the French capital's iconic buildings, the La Samaritaine department store. Duration: 01:42 Video provided by AFP
Powered by NewsLook.com
Bee Fossils Provide Insight Into Ice Age Environment

Bee Fossils Provide Insight Into Ice Age Environment

Newsy (Apr. 12, 2014) — Archeologists have found many fossils in the La Brea Tar Pits, including those of saber-tooth tigers and mammoths. Video provided by Newsy
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:
from the past week

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