The 'founder effect' theory — still controversial to many biologists — states that speciation occurs suddenly due to a small influx of colonists founding new populations, resulting in the creation of many new gene combinations and losing many others. But, in 28 May online Proceedings of National Academy of Sciences USA, Sonya Clegg and colleagues from Imperial College, London, show that single colonization events are rarely accompanied by severe founder effects and the formation of new species is a gradual and not a sudden process.

Clegg et al. analyzed DNA samples from a silvereye species-complex (Zosterops lateralis) captured on south west Pacific islands and compared them with samples from colonies on the Australian mainland and from island populations known to be founded over 3,000 years ago. They found that single founder events do not affect levels of heterozygosity or allelic diversity, nor do they result...

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