Q.What is meant by embryological evidence for evolution? Explain briefly with reference to the observation that the early embryos of fish, amphibians, reptiles, birds and mammals all pass through a stage showing gill slits.

Embryological evidence for evolution rests on the observation that the early embryos of very different vertebrate groups — fish, amphibians, reptiles, birds and mammals — closely resemble one another, far more so than the very different adult forms they eventually become; most strikingly, all these embryos develop paired gill-slit structures at an early stage, which become functional gills only in fish, while in land vertebrates the same structures are remodelled into parts of the jaw and inner ear. This pattern is best explained by all vertebrates sharing a common aquatic ancestor whose gill-forming developmental instructions have been retained, though repurposed, across all descendant lineages. Molecular evidence provides an independent confirmation: comparing the sequence of DNA bases or of a shared protein such as cytochrome-c (present, in similar form, across almost every aerobically respiring orga …