Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Human migration tracked in Stanford computer simulation

22.01.2004


Early humans migrating from Africa carried small genetic differences like so much flotsam in an ocean current. Today’s studies give only a snapshot of where that genetic baggage came to rest without revealing the tides that brought it there. Now researchers at the Stanford University School of Medicine have devised a model for pinpointing where mutations first appeared, providing a new way to trace the migratory path of our earliest ancestors.



The study was led by Luca Cavalli-Sforza, PhD, emeritus professor of genetics, who has spent most of his career tracking the evolution of modern humans. Much of his current work involves following mutations in the Y chromosome, which is passed exclusively from father to son, as humans migrated from Africa and spread to the rest of the world during the past 50,000 years.

These mutations, most of which cause no physical change, tend to appear at a constant rate, providing a genetic timer. For example, if a population has 10 mutations after 50,000 years of evolution from the common ancestor in Africa, then the fifth mutation probably arose 25,000 years ago. But where was the population located at that time? Until now genetics hasn’t had an answer.


"If we know the time when a mutation arose we know something. If we also knew the place we’d know almost everything," Cavalli-Sforza said.

With the help of senior application software developer Christopher Edmonds and statistician Anita Lillie, both researchers at Stanford, Cavalli-Sforza built a computer model to simulate how mutations spread in a migrating population. The results of this work are published in this week’s online issue of Proceedings of the National Academies of Science.

The group reduced the world’s continents to a simple rectangular grid. They populated the first few squares with computerized human populations and gave those electronic villages realistic rates for population growth, migration and mutations. The inhabitants had more than one child, on average, and those offspring could migrate to any neighboring square as long as it wasn’t filled to capacity. This population growth filled the initial squares to capacity and pushed the computerized people to migrate at a constant rate across their rectangular territory until the next space was filled.

When a mutation appeared within a population, descendants reproduced and migrated at the same rate as other individuals. Most of the mutations, however, simply disappeared due to chance.

Those mutations that stayed in the population until the simulation ended showed one of two patterns. If the mutation appeared in a heavily populated area, it had a lower chance of surviving for many generations or reaching high numbers. In these cases, the mutation remained extremely rare in the local population.

If a mutation appeared in a person at the edge of the migration front where the population was scarce, the mutation was more likely to spread through the population. The mutation-carrying person multiplied and the offspring migrated, taking the mutation to neighboring squares. If these neighboring squares were previously unoccupied, the mutated person had a high probability of reproducing and passing along the mutation. The mutation itself remained most common in the migratory wave front, a situation Cavalli-Sforza refers to as "surfing" the migratory wave.

Over the course of 64,000 simulations, the group came up with a model for finding a mutation’s origin. First they identified the mutation’s farthest edge - corresponding with a boundary such as the ocean or mountain range in human populations. Then they calculated the average area of where the mutation is distributed - called the mutation’s centroid. According to the models, the centroid is about half the distance between where the mutation arose and where it ended up.

In at least some simulations, the mutation no longer existed in the population where it first arose. Without the group’s way of estimating distance, there might be no trace of the mutation’s place of origin. Now they can generate a dated "we were here" sign to place on the route of human migration.


Stanford University Medical Center integrates research, medical education and patient care at its three institutions - Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children’s Hospital at Stanford. For more information, please visit the Web site of the medical center’s Office of Communication & Public Affairs at http://mednews.stanford.edu.

Amy Adams | EurekAlert!
Further information:
http://mednews.stanford.edu

More articles from Studies and Analyses:

nachricht Win-win strategies for climate and food security
02.10.2017 | International Institute for Applied Systems Analysis (IIASA)

nachricht The personality factor: How to foster the sharing of research data
06.09.2017 | ZBW – Leibniz-Informationszentrum Wirtschaft

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Ocean atmosphere rife with microbes

17.10.2017 | Life Sciences

Neutrons observe vitamin B6-dependent enzyme activity useful for drug development

17.10.2017 | Life Sciences

NASA finds newly formed tropical storm lan over open waters

17.10.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>