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The extinction of our close relatives, Homo neanderthalensis, is one of the big mysteries of human evolution. Could sunburn and sunburn and the resulting skin cancer be to blame? New research reveals their extinction coincides with a dip in the earth’s protective magnetic field1.

Ultraviolet radiation did the Neanderthals in

The earth’s magnetic field provides crucial protection from ultraviolet radiation. It extends far into space, where it deflects the ionising particles from the sun that can damage our DNA. This provides vital protection for our cells, preventing them from accumulating the harmful mutations that can lead to skin cancer, and also makes pretty aurora.

Under the right circumstances, aurora can be localised to a single room

However, our planet’s magnetic field is not a fixed thing. Back in the 60s, geophysicists were studying the magnetic record of ancient lava, which records what the geomagnetic field was like as the lava cooled. They noticed a shift in the Laschamp lava flow, indicative of a dramatic decrease in field strength2.

This was given the creative title of “Laschamp excursion” (because scientists are uncreative with their names) and has since been thoroughly studied. Notably, layers of sediment preserve details on the magnetic field as they’re deposited. As such, a stack of such sediments can be used to build a timeline of the field’s strength1.

Field strength over time, as measured by sediment stacks. Note the big dip at Laschamp1.

Recently, Channell and Vigliotti reviewed this record in Reviews of Geophysics (again, uncreative with the names). They found that dips in the strength of the magnetic field seemed to correlate with animal extinctions. Including the Laschamp excursion, which they could pinpoint to happening ~40,000 years ago1.

The time the Neanderthals went extinct.

Why didn’t Homo sapiens get skin cancer?

As a result of this, Channell and Vigliotti speculated that this drop in magnetic field strength (and the resulting increase in ultraviolet radiation) may have raised the risk of sunburn and skin cancer, contributing to the Neanderthal extinction1.

Close up of the Laschamp excursion (curvy line) With Neanderthal sites (purple lumps). The purple lumps disappear after the peak of the excursion1. Yes, it triggers me Homo sapiens is labelled cro-magnon.

Of course, this raises the question of why Homo sapiens wasn’t also wiped out by sunburns.

Well, how do we protect from sun damage now? With sunscreen! It turns out that this might be a pretty old invention, with ochre being used as a natural sunscreen by several African groups. In fact, this practice might stretch back into the Stone Age, with early evidence of ochre use being dated to at least 100,000 years ago3. However, there is also evidence of Neanderthals using ochre, so this might not be an advantage unique to our species.

Ovahimba women from Numibia are all about that natural sunscreen3.

So, if there weren’t cultural differences between us perhaps there were biological ones. Specifically, in our skin. It turns out that the Homo sapiens living alongside Neanderthals had darker skin than them4. In fact, interbreeding with Neanderthals may have introduced some of the genes responsible for lighter skin into modern human populations.

Ultimately, these differences in skin tone may have given Homo sapiens vital protection from ultraviolet radiation during the Laschamp excursion. Could this be why we survived and the Neanderthals didn’t?

References

  1. Channell, J.E.T. and Vigliotti, L., 2019. The role of geomagnetic field intensity in late Quaternary evolution of humans and large mammals. Reviews of Geophysics.
  2. Roperch, P., Bonhommet, N. and Levi, S., 1988. Paleointensity of the Earth’s magnetic field during the Laschamp excursion and its geomagnetic implications. Earth and Planetary Science Letters88(1-2), pp.209-219.
  3. Rifkin, R.F., Dayet, L., Queffelec, A., Summers, B., Lategan, M. and d’Errico, F., 2015. Evaluating the photoprotective effects of ochre on human skin by in vivo SPF assessment: implications for human evolution, adaptation and dispersal. PLoS One10(9), p.e0136090.
  4. Mathieson, I., Lazaridis, I., Rohland, N., Mallick, S., Patterson, N., Roodenberg, S.A., Harney, E., Stewardson, K., Fernandes, D., Novak, M. and Sirak, K., 2015. Genome-wide patterns of selection in 230 ancient Eurasians. Nature528(7583), p.499.

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