Haeckel fudged his embryo drawings — and textbooks copied them for a century

In 1868, Ernst Haeckel — a prominent German zoologist and professor at the University of Jena — published a famous series of embryo drawings. Arranged in a comparative grid, they appeared to prove his theory that 'ontogeny recapitulates phylogeny': that each creature replays its evolutionary past as it grows in the womb.

The evidence was fudged. As the biologist Matthew Cobb wrote in New Scientist in 2015, Haeckel 'placed the drawings into a comparative grid, highlighting similarities between species and blurring differences' — and 'the results are highly inaccurate.'

Critics were not fooled for long. From the 1870s, expert critics accused Haeckel of drawing the embryos more alike than they really are. German colleagues exposed the deception and pressured him into admitting it — he blamed his draftsman, and the admission was soon forgotten, with no proper retraction.

The images outlived the correction. Textbooks 'copied and recopied them through the 20th century' — including postwar textbooks in Britain and the United States and Scott F. Gilbert's developmental-biology textbook as late as 1985. In 1997, the British biologist Michael Richardson compared Haeckel's figures with real embryos and exposed them once more. A century after the fraud, it became the textbook case of scientific fraud.

Haeckel drew embryos more alike than they are, and textbooks recopied the fakes until 1997, when Richardson compared them with real embryos and exposed them once more.

He fudged the evidence to make his theory look airtight: the comparative grid highlighted similarities between species and blurred differences, and the resulting drawings were highly inaccurate.

The retraction failed: under pressure he admitted the drawings were wrong but blamed his draftsman, and no clean correction followed — so the fakes stayed in circulation.

Textbooks recopied the images for over a century without checking them against real embryos; a popular theory kept the fakes alive long after experts had exposed them.

It took a direct comparison with real specimens, in 1997, to finish what the critics of the 1870s had started.

A doctored figure that flatters a popular theory survives its critics: exposed in the 1870s, Haeckel's fakes still ran in textbooks in 1997.

The drawings were copied and recopied through the 20th century, including postwar textbooks in Britain and the United States and Scott F. Gilbert's 1985 textbook. In 1997, the British biologist Michael Richardson showed how far the figures diverged from real embryos, and the affair became one of the best-known cases of scientific fraud — still invoked today in debates over evolution and textbook accuracy. Haeckel's scientific standing never recovered from the episode.