Editing Recapitulation theory (section)

=== Modern status ===

Modern [[evolutionary developmental biology]] (evo-devo) follows von Baer, rather than Darwin, in pointing to active evolution of embryonic development as a significant means of changing the [[morphology (biology)|morphology]] of adult bodies. Two of the key principles of evo-devo, namely that changes in the timing ([[heterochrony]]) and positioning ([[heterotopy]]) within the body of aspects of embryonic development would change the shape of a descendant's body compared to an ancestor's, were first formulated by Haeckel in the 1870s. These elements of his thinking about development have thus survived, whereas his theory of recapitulation has not.<ref>{{cite journal |last1=Hall |first1=B. K. |title=Evo-Devo: evolutionary developmental mechanisms |journal=International Journal of Developmental Biology |date=2003 |volume=47 |issue=7–8 |pages=491–495 |pmid=14756324}}</ref>

The Haeckelian form of recapitulation theory is considered defunct.<ref name=Lovtrup>{{cite journal | last1=Lovtrup | first1=S | year=1978 | title=On von Baerian and Haeckelian Recapitulation | journal=Systematic Zoology | volume=27 | issue=3| pages=348–352 | doi=10.2307/2412887| jstor=2412887 }}</ref> Embryos do undergo a period or [[phylotypic stage]] where their morphology is strongly shaped by their phylogenetic position,<ref>{{Cite journal|last1=Drost|first1=Hajk-Georg|last2=Janitza|first2=Philipp |last3=Grosse |first3=Ivo  |last4=Quint |first4=Marcel | year=2017|title=Cross-kingdom comparison of the developmental hourglass|journal=Current Opinion in Genetics & Development|volume=45|pages=69–75|doi=10.1016/j.gde.2017.03.003|pmid=28347942|doi-access=free}}</ref> rather than selective pressures, but that means only that they resemble other embryos at that stage, not ancestral adults as Haeckel had claimed.<ref name="Kalinka2012">{{Cite journal | last1=Kalinka | first1=A. T. | last2=Tomancak | first2=P. | title=The evolution of early animal embryos: Conservation or divergence? | doi=10.1016/j.tree.2012.03.007 | journal=Trends in Ecology & Evolution | year=2012 | volume=27 | issue=7 | pages=385–393| pmid=22520868 | bibcode=2012TEcoE..27..385K }}</ref> The modern view is summarised by the [[University of California Museum of Paleontology]]:

{{Blockquote|Embryos do reflect the course of evolution, but that course is far more intricate and quirky than Haeckel claimed. Different parts of the same embryo can even evolve in different directions. As a result, the Biogenetic Law was abandoned, and its fall freed scientists to appreciate the full range of embryonic changes that evolution can produce—an appreciation that has yielded spectacular results in recent years as scientists have discovered some of the [[Evo-devo gene toolkit|specific genes that control development]].<ref>{{citation | title=Early Evolution and Development: Ernst Haeckel | series=Evolution 101 | publisher=University of California Museum of Paleontology | url=http://evolution.berkeley.edu/evosite/history/early_evodevo.shtml | access-date=2013-02-20 | url-status=dead | archive-url=https://web.archive.org/web/20121222105021/http://evolution.berkeley.edu/evosite/history/early_evodevo.shtml | archive-date=2012-12-22 }}</ref>}}