“…Indeed, the circuitry for controlling stepping is assembled very early in embryonic life. Many vertebrates including tadpoles (Stehouwer & Farel, 1985), chicks (Narayana & Hamburger, 1971; O'Donovan, Sernagor, Sholomenko, Ho, Antal & Yee, 1992), rats (Kudo, Ozaki & Yamada, 1991; Greer, Smith & Feldman, 1992; Robinson & Smotherman, 1992) and cats (Graham Brown, 1915; Windle & Griffen, 1931) show spontaneous or induced stepping movements with clear alternating flexor and extensor activity early in embryonic life (reviewed in Sillar, 1994). The ability to locomote soon after birth must have been an important evolutionary advantage in many animals.…”