Evolution: Origin of Life and Evidences — Part 2: Embryology, fossils, biogeography and molecules: visual lesson, ISC Class 12 Biology

Lesson

More lines of evidence

Part 2 — evidence from embryos, fossils, the distribution of organisms and their molecules.

In this lesson you will

Explain the embryological evidence and the idea of recapitulation
Explain how fossils are dated by radiocarbon dating and relate eras to their dominant life
Use biogeographical and molecular evidence, and explain adaptive radiation

Concept

Embryological evidence

Embryos of fish, amphibians, reptiles, birds and mammals look alike in early stages: all have gill slits (pharyngeal pouches), a notochord and a tail. Ernst Haeckel proposed the recapitulation theory: ontogeny recapitulates phylogeny — development of an individual repeats the evolutionary history of its group.

Table of embryological observations and interpretations
Observation	Interpretation
Gill slits in a human embryo	Inherited from fish-like ancestors
Tail in early mammal embryos	Shared ancestry with tailed vertebrates
Embryos resemble embryos, not adults, of other groups (von Baer)	Recapitulation is not literal; it shows common descent

Concept

Fossils and how they form

Fossils are remains or traces of organisms preserved in rocks. Older rock layers (strata) lie deeper and hold simpler forms. Archaeopteryx, with feathers and wings like a bird but teeth, claws and a long bony tail like a reptile, is a connecting link between reptiles and birds.

Table of kinds of fossils
Kind of fossil	Example
Petrified remains	Bones and wood replaced by minerals
Moulds and casts	Shells leaving impressions
Preserved whole	Insects in amber, mammoths in ice
Trace fossils	Footprints, burrows

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