embryo on dark blue backgraund

How viruses shape our world

COVID-19 is a reminder of their destructive power, but they’re crucial to humans’ development and survival.

Although feared as agents of disease, viruses also work wonders, shaping evolution from the very beginning. About 8 percent of our DNA comes from viruses that infected our long-ago ancestors and patched viral genes into their genomes. Some of these genes now play crucial roles in the early stages of the developing embryo and the placenta that surrounds this 13-week-old fetus.
Photograph by LENNART NILSSON, TT/SCIENCE PHOTO LIBRARY (COMPOSITE OF TWO IMAGES)
This story appears in the February 2021 issue of National Geographic magazine.
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