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The Biogenetic Law of Ernst Haeckel

Ernst Haeckel's Biogenetic Law, also called the theory of recapitulation, was put forth in 1866. Though it's been largely discredited, it is partly accurate. Haeckel stated his theory as "Ontogeny recapitulates phylogeny." Ontogeny is the embryological development process of a species; phylogeny is the evolutionary history of a species. He meant that the embryological development of the young in any given species reflects the evolutionary history of that species.

There are indeed similarities between ontogeny and phylogeny. However, Haeckel's embryo drawings produced to support his theory overemphasized certain similarities and de-emphasized dissimilarities.

For example, the human embryo at one point seems to have gill slits in the neck, thought by Haeckel to signify a fishlike stage in development. However, gill slits are not gills, and the similarity is not an actuality. In reality, the "gill slit" develops into the lower jaw in mammals.

Despite its problems, Haeckel's biogenetic law did help scientists note certain things in embryology that apparently have a very old genesis. In addition, when we know the evolutionary history of a species, there is definitely some correspondence with the ontology: for instance, whales, which evolved from land mammals with legs, have embryonic legs that develop, then recede into the vestigial organs they are in adult whales.

Many evolutionary scientists avoid Haeckel's biogenetic law because its innacurracies are sometimes used to discredit Darwinian evolution.

Web Resources On The Biogenetic Law of Ernst Haeckel

Haeckel and the Vertebrate Archetype
Haeckel and his Embryos

Book Resources On The Biogenetic Law of Ernst Haeckel

The History of creation, or, The development of the earth and its inhabitants by the action of natural causes by Ernst Heinrich Philipp August Haeckel
The evolution of man: A popular exposition of the principal points of human ontogeny and phylogeny by Ernst Heinrich Philipp August Haeckel

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