Question

Define biogenetic law.

Answer 1

Hint:  The theory proposes that evolutionary stages are repeated in the growth of a young animal. It is also commonly known as recapitulation theory.

Complete Answer:

- Ernst Haeckel postulated the biogenetic law. It states that ontogeny recapitulates phylogeny,that is,in animal species the early stages of development resemble one another, with the species gradually diverging as evolution progresses. 

- According to Haeckel, the biogenetic law depends on three hypotheses. The law of correspondence, considered as the first hypothesis. It states that each stage of development of higher animals, such as humans, corresponds to the adult stage of lower animals, such as fish. 

- For instance, the gill slits of early human embryos relate with the gill slits of adult fish. The second hypothesis was that phylogenesis would occur with the inclusion of new features to the normal developmental end stage. It refers to the evolutionary history of a species. 

- Haeckel said that during early development, the early stages of the embryos of different species appear identical to each other due to evolutionary limitations. These restrictions vanish near the end of development, allowing new characters to be introduced and future evolution to occur. The third assumption was the truncation principle. 

- Haeckel proposed that the duration of embryonic growth would gradually grow longer than the gestation cycles of organisms in developed species if new characters were continually introduced at the end of natural ontogenesis. As a result, he theorised that in higher species, early growth periods would be quicker than in lower ones.

Note: The biogenetic law was suggested by Haeckel so that researchers could use the embryological growth stages to help create evolutionary (phylogenetic) trees. The biogenetic rule was introduced by Haeckel after reading the theories of Charles Darwin's The Origin of Species.