As far as we know, humans are the only living things that wear watches.
But we aren’t the only ones that can tell time.
Earth’s movement sets the rhythms of countless biological clocks.
The 24 hour solar period winds cellular gears controlling sleep, hunger, and metabolism
in creatures ranging from jellyfish to elephants.
And our 365-and-a-quarter-day journey around the sun regulates cycles of seasons, harvests,
and migrations.
But the phases of our planet’s nearest neighbor also have a surprising pull on biological
rhythms.
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For many species the moon’s glow is a cue that’s crucial to their survival.
Vampires and emo teenagers aren’t the only ones who find moonlight romantic.
Lots of animals use the 29-and-a-half day lunar cycle to sync up when it comes to finding
a mate.
Triggered by the full moon, impalas roar, which in turn triggers all their female mates
to begin ovulation.
Using a common signal like this ensures every member of a species goes looking for a partner
at the same time.
Lunar cycles are especially important in the sea.
Marine bristle worms live on rocky shorelines, where they rise to the water’s surface under
the dim light of the new moon.
The worms mass together, swirling around one another and release their gametes in sync.
This big mating party increases the chances that any one worm will contribute to the next
generation.
Some eels also reproduce all at once, and rely on the dim light of the new moon to avoid
predators.
The moon also controls the tides, and that pull can help some animals’ eggs and larvae
develop and survive.
Fish called grunion lay their eggs high up on beaches during high tides, where the sand
protects the eggs as they develop.
They hatch when the next cycle of high tides washes them out to sea.
But what *controls* these living lunar cycles?
These species must have an inner moon clock.
When scientists raised marine worms in constant light or darkness, they didn’t try to reproduce.
But when they gave them artificial light on a lunar schedule, the worms did their mesmerizing
mating dance.
The scientists found special neurons in the worms’ brains that respond to light, linked
to timing genes that control these lunar behaviors.
The moon seems to act like a signal that supercharges the worms’ desire to mate when the light
at night is just right.
But the moon is more than just a clock.
It transforms ecosystems.
The full moon is 100 times brighter than the new moon.
This lets animals see their prey, forage, and navigate better.
But all that light can be risky.
Many species of frogs avoid calling to their friends during the full moon, since the extra
light makes it more vulnerable to predators.
And all the manmade light sources now flooding the night could provide a fake, full-time
full moon that might throw ecosystems out of whack.
So what about us?
Women’s reproductive cycles are about the same length as the lunar cycle, but scientists
think that’s probably just a coincidence.
If human menstrual cycles were, in fact, linked to the moon, why not our great ape sisters?
Now that millions of women are using apps to track menstrual periods, it’s become
pretty clear there’s likely no connection.
So for antelopes, coral, fish, and even wildebeest on the Serengeti, the phases of life are set
by phases up above.
Next time you take a look at that fancy clock in your pocket, remember that you aren’t
the only creature on Earth who relies on a satellite to know what time it is.
Stay curious.
Yes.
Technically speaking, moonlight is just sunlight.
So you can stop typing that comment.
And no, there’s no such thing as werewol