There’s something that’s been puzzling scientists for a while.
We knew that modern humans originally came from Africa about 200,000 years ago, but...
we didn’t really know when we left.
According a paper published this week in Nature, teeth found in Fuyan Cave in the Hunan Province
of China puts prehistoric modern humans, or homo sapiens, in southern China more than
eighty thousand years ago.
That’s at least 30,000 years earlier than most scientists thought. There were models
of human migration that put homo sapiens in China that long ago, but they never had substantial
evidence until now.
It’s also 30 to 70 thousand years before modern humans reached Europe.
The 47 teeth found in Fuyan Cave came from at least 13 people, and they’re shaped almost
exactly like the teeth found in the mouths of modern Chinese people today. So these are
definitely homo sapiens.
And they were found beneath a layer of flowstone that was at least 80,000 years old. That’s
the smooth stone you see inside old limestone caves, that forms into the stalactites and
stalagmites sticking out of the ceiling and floor.
Since we can measure how long it takes those things to form by studying the geology of
the cave they’re found in, we can use them to date whatever’s underneath them -- like
teeth.
A stalagmite in Fuyan Cave that was on the layer above the new fossils was dated as being
between 80,000 and 120,000 years old. So the people who left those remains must have died
before that.
In the same layer of sandy clay under the flowstone, where we found the modern human
teeth, there were ALSO fossils from a number of animals that lived during the Upper Pleistocene
period -- 125,000 to 10,000 years ago.
So if these people were contemporaries of those animals - which they were, if they died
around the same time, and left remains in the same layer of clay - that means they can’t
be more than 125,000 years old.
Thanks to these teeth, we know that modern humans probably first left Africa around 80,000
years ago and spread to the Eastern Mediterranean and Southern China. Then, around 40,000 years
ago, they went from the Eastern Mediterranean to Northern China and Europe.
When you think about it, it makes sense: modern humans originated in a tropical African climate.
It would have been a lot easier for them to adapt to the conditions they found in southern
Asia than in the northern Mediterranean or Europe, where temperatures regularly reached
sub-zero.
Expanding north also would have meant competing with the Neanderthals, who were well-entrenched
in Europe, and much hardier in the cold.
But enough about people! Let’s talk about eels.
According to a study in Nature Communications, electric eels use their zap both as a weapon
and a tracking device.
We’ve talked about how that zap works before. Electric eels have long chains of special
cells called electrocytes that are all linked to a common nerve.
When the eel sends a signal down that nerve, all of the electrocytes open at once, creating
a current capable of discharging at around 700 volts. That’s enough to stun or kill
whatever the eel wants to eat.
We understand how they shock things. What we didn’t understand until this study is
how they found those things after they shocked them.
Electric eels live in thick, dark, muddy water in the Orinoco River and the Amazon basin
in South America. There is very little visibility down there, and because of that, electric
eels have evolved to have very weak eyesight. They navigate, and hunt, by sensing the electric
fields around them.
But once they’ve zapped their prey, it kind of just floats wherever the water wants to
take it. So if they can’t see it, and they can’t sense it, how do they get it in their
mouths?
What we know now is that electric eels are much more sophisticated hunters than we thought.
They don’t just zap everything in the water around them and then scoop up the tasty debris.
Instead, they send a small electric pulse through the water. Just enough to make a tiny
fish twitch. That twitch is their electric field responding to the current. That’s
something the eels can detect.
Then, as the eels strike, they emit a high-voltage, highly accurate volley of electrical discharges
aimed directly at their prey. So the electricity functions as both a stun, and as a homing
signal.
It’s similar to how echolocating bats will use high frequency sound to zero in on their prey.
The researchers tested this by taking a spinning disk and putting one conductive rod, and lots
of non-conductive plastic rods, inside it.
When the eel sent out an electric pulse, the conductive rod would twitch -- so that’s
what it tried to eat.
The team found that if an electric eel can’t see or smell its prey at all, it will only
strike towards prey that responds to that electric signal. And they’ll always miss
prey that doesn’t.
Turns out that electric eels are more like electro-locating homing eel-bats with stun guns.
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