How Scientists Use Teeny Bits of Leftover DNA to Solve Wildlife Mysteries

Scoop a glass of water out of your backyard stream and hold it up to the light.
Those muddy, swirling waters are full of invisible traces of life. From the dinky goldfish pond at the mall to the waves lapping at the seashore, every body of water is a slurry of sloughed-off cells. What’s more, scientists have recently devised methods by which they can sift out the DNA sequences in that slurry to differentiate between a blue crab, a blue whale or even a Loch Ness Monster—without ever laying an eye on the animal itself.
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