The naturalist Charles Robert Darwin, the geologist Charles Lyell and the botanist Joseph Dalton Hooker are depicted in this 19th century painting. De Agostini/A.C. Cooper/Getty Images hide caption

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Koko, seen here with Penny Patterson (left) at age 4 1/2 — nearly 40 years ago — was taught sign language. June Monroe, an interpreter for the deaf at St. Luke's Church who helped teach Koko, is in the center. Bettmann Archive/Getty Images hide caption

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This image shows the galaxy MCS J0416.1–2403, one of six clusters targeted by the Hubble Frontier Fields program. The varying intensity of blue haze in this image is a mass map created by using new Hubble observations combined with the magnifying power of a process known as gravitational lensing. M. Jauzac, J-P. Kneib and the CATS collaboration/ESA/Hubble/NASA hide caption

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A tourist at the Bradbury Science Museum in Los Alamos, New Mexico, in February examines a full-size replica of the "Fat Man" atomic bomb which was dropped on Nagasaki, Japan, on Aug. 9, 1945. Los Alamos is home to the Los Alamos National Laboratory which was established in 1943 as part of the Manhattan Project. Robert Alexander/Getty Images hide caption

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"Self-regulation is about identifying the causes and reducing the intensity of impulses and, when necessary, having the energy to resist," psychologist Stuart Shanker writes in his book, Self-Reg: How to Help Your Child (and You) Break the Stress Cycle and Successfully Engage with Life. LA Johnson/NPR hide caption

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