History in pairs

A Timeline of Twins and Doubles

Twins have fascinated people for as long as there have been people. This timeline picks out the moments when twins, and doubles of all kinds, changed what we know.

Engineers testing a Voyager spacecraft at NASA's Jet Propulsion Laboratory

Voyager being tested: JOHN GREGOIRE, NASA/JPL, Public domain

Twins through time

1811
Chang and Eng are born
The conjoined twins born in Siam later give the world the phrase Siamese twins.
1875
Galton's twin study
Francis Galton proposes using twins to compare the effects of nature and nurture.
1916
Freemartins explained
Frank Lillie shows that shared blood between twin calves explains the freemartin.
1931
A twin in the stratosphere
Auguste Piccard becomes one of the first two people to reach the stratosphere. His twin Jean follows in 1934.
1965
Project Gemini
NASA's two-person spacecraft programme, named after the twin stars, begins crewed flights.
1977
The Voyager twins launch
Voyager 2 and Voyager 1 leave Earth weeks apart for the outer planets.
1978
Charon is discovered
Pluto turns out to have a moon half its size, making a double world.
1979
The Jim twins
Identical twins separated at birth are reunited at 39, launching the Minnesota Study of Twins Reared Apart.
1996
Dolly the sheep
The first mammal cloned from an adult cell is born in Scotland, a twin made in the lab.
2004
Twin rovers on Mars
Spirit and Opportunity land three weeks apart and go on to outlast their 90-day missions many times over.
2007
Semi-identical twins
The first case of twins from one egg and two sperm is reported in the United States.
2012
Interstellar space
Voyager 1 becomes the first spacecraft to leave the Sun's bubble of solar wind. Voyager 2 follows in 2018.
2015
New Horizons at Pluto
The first close-up photos of Pluto and Charon reveal a heart of ice and a red-capped moon.
2019
A second semi-identical pair
Doctors in Brisbane describe semi-identical twins identified during pregnancy.