“…Placental lactogen hormones probably appeared about 75 million years ago (Martal, 1980) from a duplication of the growth hormone cistron. Though most of the members of this hormone family have specific biological properties, some of them such as hGH (Li, 1972), ovine PL Djiane, 1975, 1977 ;Martal, 1978), bovine PL (Murthy et al, 1982) or primate PL (Josimovitch and Mac Laren, 1962;Friesen, 1965;Kaplan and Grumbach, 1965 ;Florini et al, 1966 ;Shome and Friesen, 1971 ) Primate GH is the only animal GH efficient in humans. However, the memory of its common ancestral origin with the GH of other species is found both in the high percentage of identical primary structures (table 1 ) and in the fact that certain fragments of non-human GH exert a more or less pronounced biological effect in humans (Liberti and Miller, 1978 ;Maciag et al, 1980 ;Hubbard and Liberti, 1980).…”