Question

Explain the saying “ontogeny repeats phylogeny.”

Answer 1

Hint: Ontogeny refers to origination and development of an organism that occurs from time of fertilization of egg to adult. Phylogeny is a tree or a branching diagram that shows the evolutionary relationship among various biological species based on similarities and differences between them.

Complete answer:
Ontogeny repeats phylogeny was expressed by Ernst Haeckel which explains that the development of embryo of an organism from fertilization to gestation goes through various stages of growth and development that resembles successive adult stages in the evolution of the organism's remote ancestors. The various stages from fertilization of an organism is known as ontogeny and resemblance with remote ancestors is known as phylogeny. This theory is also known as theory of recapitulates or biogenetic law.
The concept of recapitulates phylogeny has been applied to many areas like cognitive development that states that if there be an order in which the human race has mastered its various kinds of knowledge, there will arise in every child an aptitude to acquire these kinds of knowledge in the same order- Herbert Spencer. Therefore, development characters along with other traits and lines of evidence can be used for constructing phylogenies. This approach can also help in finding our ancestors and can give a link of how evolution occurred on Earth.

Note: As the embryos evolve in different ways it leads to shortcomings of this theory which are recognized later on. Modern evolution theory believes that to activate evolution of embryonic development as significant means of changing the timing and position within the body aspect.