# Great white sharks’ DNA puzzle upends migration theory, study finds
*Apex predator, baffling genetics: the migration theory no longer fits.*
Scientists have overturned a key idea about how great white sharks spread across the oceans. A global genetic analysis, reported 16 August 2025, finds that the long‑favoured migration‑and‑breeding explanation cannot account for a striking mismatch between the sharks’ nuclear and mitochondrial DNA. The team says the result leaves an open question at the heart of white shark evolution and conservation.
## What the researchers actually found
A new analysis indicates great whites were squeezed into a single Indo‑Pacific population by the end of the last ice age around 10,000 years ago, then expanded and split. Divergence began roughly 7,000 years ago, leaving today’s sharks in three broad populations — southern hemisphere (around Australia and South Africa), the North Atlantic and the North Pacific — despite a global range.
## Why the go‑to migration theory fails
For two decades, the leading idea was sex‑biased dispersal: males roam widely while females show breeding‑site fidelity (philopatry). That should yield similar nuclear DNA but distinct mitochondrial DNA between regions. In this study, the expected signal did not appear in the nuclear genome, and time‑scale tests showed philopatry alone could not produce the observed mitochondrial split.
## Other suspects ruled out
The team tested reproductive skew — where only a few females contribute most offspring — and found it did not fit. Pure genetic drift also fails, because it would affect both nuclear and mitochondrial DNA; here the mismatch is selective to mitochondria. That leaves natural selection as a remote possibility that, if true, would need to be exceptionally strong.
## Why it matters now
Great whites remain relatively sparse. “There are probably about 20,000 individuals globally,” said Gavin Naylor of the Florida Museum of Natural History. The mystery shapes how scientists read shark history, movement and resilience. As Naylor noted: “The honest scientific answer is we have no idea.”
### Takeaway
A flagship explanation for great white genetics has been tested — and found wanting. Solving what drives the DNA mismatch now becomes central to understanding and protecting these sharks.
Read the original report via ScienceDaily: [Great white sharks have a DNA mystery science still can’t explain](https://www.sciencedaily.com/releases/2025/08/250816113505.htm).