The biogenetic law, often summarised as “ontogeny recapitulates phylogeny”, was originally proposed by which biologist?

Introduction / Context:
The biogenetic law is a historical concept in evolutionary biology that attempted to link the development of an individual organism with the evolutionary history of its species. It is commonly summarised by the phrase “ontogeny recapitulates phylogeny”. Although modern biology recognises that this statement is an oversimplification, the idea remains important from a historical perspective. This question tests your knowledge of which biologist first formulated and popularised this law.

Given Data / Assumptions:

The term biogenetic law refers to a relationship between individual development (ontogeny) and evolutionary history (phylogeny). The famous phrase associated with it is “ontogeny recapitulates phylogeny”. Options list several key figures in biology and evolution: Wallace, Darwin, Haeckel, Lamarck and Mendel. We assume standard historical attributions used in evolutionary biology.

Concept / Approach:
Ernst von Haeckel, a German biologist of the nineteenth century, formally proposed the biogenetic law. He suggested that the embryonic development of an organism passes through stages that resemble the adult forms of its evolutionary ancestors. While modern embryology has shown that this is not literally true, Haeckel's idea stimulated significant research in comparative embryology. Darwin and Wallace jointly proposed the theory of natural selection, Lamarck is associated with inheritance of acquired characters, and Mendel is the father of genetics; none of them specifically proposed the biogenetic law.

Step-by-Step Solution:
Step 1: Link the phrase “ontogeny recapitulates phylogeny” with the name Haeckel, as often mentioned in textbooks. Step 2: Recall that Darwin and Wallace are best known for natural selection, not for detailed embryological laws. Step 3: Recognise that Lamarck preceded Darwin and proposed use and disuse theory and inheritance of acquired characters. Step 4: Remember that Mendel worked on pea plants and elucidated the laws of inheritance, becoming the father of genetics. Step 5: Conclude that Ernst von Haeckel is the correct match for the biogenetic law.

Verification / Alternative check:
Another check is to think about typical exam tables that pair scientists with their contributions. Haeckel is always mentioned with the biogenetic law and the statement that an organism's development reflects its evolutionary history. Darwin is listed with the book On the Origin of Species and natural selection, Lamarck with his theory of use and disuse, Wallace as co discoverer of natural selection, and Mendel with Mendelian laws. Since only Haeckel is consistently associated with the biogenetic law, this confirms your choice.

Why Other Options Are Wrong:
Alfred Russel Wallace independently arrived at the idea of natural selection but did not propose the biogenetic law. Charles Darwin made only cautious comments about embryology and never stated that ontogeny literally repeats phylogeny. Lamarck’s main idea centred on the inheritance of acquired traits, not on embryonic recapitulation. Gregor Mendel focused on genetic inheritance patterns in pea plants and did not formulate laws about developmental stages mirroring evolutionary history. Therefore, none of these alternatives fits the description given in the question.

Common Pitfalls:
A common mistake is to attribute almost every evolutionary idea to Darwin because of his central role in biology. Another pitfall is mixing up Haeckel with Lamarck or Wallace due to unfamiliarity with nineteenth century scientists. To avoid this, remember a simple association: Haeckel equals biogenetic law and ontogeny recapitulates phylogeny, Darwin and Wallace equal natural selection, Lamarck equals acquired characters and Mendel equals genetics. Having these key links clear in your mind makes such matching questions much easier.

Final Answer:
The biogenetic law was proposed by Ernst von Haeckel.