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CISCEISC (Science) ISC Class 12
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Syllabus

Embryological Evidences

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Estimated time: 10 minutes
CISCE: Class 12

Definition: Embryology

Embryology, the study of the development of an organism from egg to adult, also provides evidence for organic evolution.

CISCE: Class 12

Embryological Evidence of Evolution

  • Early embryos of different vertebrates (fish, amphibians, reptiles, birds, and mammals) closely resemble one another in overall structure.
  • Embryos of higher vertebrates pass through stages that resemble the adult or late embryonic stages of lower vertebrates.
  • Such similarity is best explained by the idea that all vertebrates have evolved from a common ancestor.
CISCE: Class 12

Common Developmental Features in Vertebrate Embryos

  • All vertebrate embryos develop from a single egg cell and pass through similar stages such as zygote, blastula, and gastrula.
  • Notochord appears in the embryos of all chordates; in vertebrates, it is later replaced by the vertebral column.
  • Gill slits/pharyngeal arches are present in all vertebrate embryos; they form gill structures in fish and are modified into other structures in land vertebrates.
  • Embryos often show a tail bud even in species whose adults have little or no visible tail.

A-F. Similarities in the embryos of some vertebrates:

CISCE: Class 12

Temporary Embryonic Structures

  • Temporary embryonic structures are present during early development but disappear or are modified in the adult.
  • Examples include the notochord, gill clefts (pharyngeal arches), and embryonic tail.
  • These structures provide clues to ancestral forms and support organic evolution.
CISCE: Class 12

Significance of Embryological Evidences

  • Strong similarity in early embryos of diverse vertebrates suggests a common basic developmental plan.
  • Embryology shows that complex vertebrates retain traces of ancestral structures during development.
  • Therefore, comparative embryology is considered important evidence in favour of organic evolution.
Maharashtra State Board: Class 10
CISCE: Class 12

Key Points: Embryological Evidences

  • Embryology provides evidence for evolution by showing that early embryos of different vertebrates closely resemble one another.
  • Embryos of higher vertebrates resemble the adult stages of lower vertebrates, indicating common ancestry.
  • All vertebrate embryos develop notochord and gill clefts, which later modify or disappear, showing evolutionary relationships.
  • Similar developmental stages of organs like the heart and brain in vertebrates support the idea that they evolved from a common ancestor.
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