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Ernst Heinrich HaeckelErnst Haeckel

proponent of "recapitulation"

Ernst Heinrich Philipp August Haeckel was born in Potsdam, Germany, in 1834, and grew up in nearby Merseburg. He developed an interest in nature at an early age and was especially fond of botany, but studied medicine at his father's insistence instead; he studied at Würzburg and Berlin, and received his medical degree from the University of Berlin in 1857. He opened a medical practice in Berlin, but did not enjoy the profession and chose to return to school in Jena instead. He became professor of comparative anatomy at the University of Jena in 1862 and chair of zoology in 1865; he spent the rest of his professional life at Jena.

Haeckel spent much of the early part of his career studying invertebrates, with emphasis on Radiolaria (diatoms), and was responsible for naming thousands of new species between 1859 and 1887. His work resulted in the publication of many monographs, including Radiolaria (1862), Siphonophora (1869), Monera (1870) and Calcareous Sponges (1872), as well as several Challenger reports, such as Deep-Sea Medusae (1881), Siphonophora (1888), Deep-Sea Keratosa (1889) and Radiolaria (1887).

Haeckel is best known for General Morphology (1866), in which he attempted to work out the practical implications of evolutionary theory in a general way. The book did not sell well, so he rewrote it in a more popular form and republished it as The Natural History of Creation in 1868; the reworked version sold very well. Although Haeckel accepted the theory of mechanical evolution proposed by Charles Darwin, he did not subscribe to Darwin's theory that natural selection was the mechanism of evolution. Like predecessor Jean Baptiste Pierre Lamarck, Haeckel believed that evolution is driven by environmental influences, but, unlike Lamarck, he did not believe that the use or disuse of any given part directly led to that part's enhancement or reduction.

Haeckel's drawings showing that the embryos of different animals are remarkably similar in their earliest stagesAs part of his research, Haeckel studied the embryos of many different kinds of animals and made drawings, many of which are still used in biology books. Seeing that the embryos of very different types of animals often looked remarkably similar during their earliest stages of development, he formulated his theory of recapitulation. According to this theory, each animal repeats the changes its ancestors underwent. For example, if a land animal had ancestors which lived in water and used gills, then each embryo of that animal continues to develop gills, even though the gills may be lost during later stages of development. He explained this and other theories in his widely read book The Riddle of the Universe (1899).

left: Haeckel's drawings showing that the embryos of different animals are remarkably similar in their earliest stages

Haeckel's 'family tree' of animal lifeHaeckel was also the first to draw a "family tree" of animal life, showing the supposed relationships of the various animal groups. He divided the whole of animal creation into two categories -- the Protozoa or unicellular animals, and the Metazoa or multicellular animals, and he pointed out that while the former remain single-celled throughout their existence, the latter are only so at the beginning, and are subsequently built up of innumerable cells, the single primitive egg-cell (ovum) being transformed by cleavage into a globular mass of cells (morula), which first becomes a hollow vesicle and then changes into the gastrula. The simplest multicellular animal he conceived to resemble this gastrula with its two primary layers, ectoderm and endoderm, and the earliest hypothetical form of this kind, from which the higher animals might be supposed to be actually descended, he called the "gastraea." His writings on this theory were published as Studies on the Gastraea Theory (1873-84).

right: Haeckel's family tree of animal life

Although most of Haeckel's theories have long since been discredited, he is still considered a pioneer in the natural sciences and some of the terms he coined are still in use today, including anthropoheny, ecology, phylum, phylogeny, and Protista. He died in Jena in 1919.

SEE ALSO
Jean Baptiste Pierre Lamarck
Protozoa

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This page was last updated on 01/10/2017.