For over two decades, scientists have been puzzled by this genetic anomaly. Three major populations of white sharks show striking variation in mitochondrial DNA, despite nearly identical nuclear DNA. Early on, migration patterns seemed to explain the mismatch. But new research, published in Proceedings of the National Academy of Sciences, has upended that theory.<\/p>\n
Origins After the Ice Age<\/strong> Today, those populations live in the southern hemisphere near Australia and South Africa, the northern Atlantic, and the northern Pacific. But their total global population is tiny\u2014around 20,000 individuals, according to study co-author Gavin Naylor of the Florida Museum of Natural History. \u201cThere are more fruit flies in any given city than there are great white sharks in the entire world,\u201d he noted.<\/p>\n An Unexpected Discovery<\/strong> The prevailing explanation was female philopatry\u2014the tendency of females to return to the same place to breed\u2014paired with wide-ranging male migrations. This could keep nuclear DNA uniform (thanks to roaming males) while allowing mitochondrial DNA to diverge (since it\u2019s passed down from females).<\/p>\n Theory Overturned<\/strong> That leaves only one possible explanation\u2014natural selection. But here\u2019s the twist: for natural selection to be responsible, given the sharks\u2019 small population sizes, it would need to be \u201cbrutally lethal,\u201d Naylor said. In other words, any deviation from the dominant mitochondrial DNA sequence would have to be fatal, preventing it from being passed on.<\/p>\n Case Still Open<\/strong> If you would like to write for The Daily Jaws, please visit our \u2018work with us<\/a>\u2019 page<\/p>\n For all the latest Jaws, shark and shark movie news, follow The Daily Jaws on Instagram<\/a>, Twitter <\/a>and Facebook<\/a>. <\/p>\n
The mystery traces back to the end of the last Ice Age, about 10,000 years ago. Back then, lower sea levels confined white sharks to a single Indo-Pacific population. As the climate warmed, sharks dispersed to new regions, and by roughly 7,000 years ago, they had split into three genetically distinct groups.<\/p>\n
In 2001, researchers studying sharks from Australia, New Zealand, and South Africa found something odd: nuclear DNA was almost identical across all samples, but mitochondrial DNA in South African sharks differed significantly from that in Australian and New Zealand sharks.<\/p>\n
The new study revisited the question with updated DNA analyses, directly testing the philopatry theory. The results were clear: migration patterns could not account for the mitochondrial differences.<\/p>\n
The researchers stress that natural selection is not yet a confirmed answer. Genetic drift is ruled out, migration is off the table, and the selection hypothesis still needs strong evidence. For now, the genetic divide in white sharks remains an open case\u2014one of the ocean\u2019s most enduring scientific mysteries.<\/p>\n