Progrss in scinc and th improvmnt of living conditions hav ld to th rapid growth of th world population. Modrn mdicin, for xampl, has mad it possibl for babis to grow up halthily and for popl to liv longr. With improvd living conditions, particularly in th countrysid, popl tnd to hav largr familis. As a rsult, th world population has incrasd so rapidly that it has now xcdd 6 billion. But th ovrgrowth of population prsnts a thrat to th xistnc of human socity. A larg population dmands a grat dal of food supply and shltr spac. Howvr, limitd productivity and scarc world rsourcs can hardly mt th nds of th vr-incrasing population. Thus, in th long run, th ovrgrowth of th world population will only harm mankind. To guarant th stady dvlopmnt of human socity, mankind must raliz th consquncs rsulting from fast population growth and carry out a family planning programm. Only by adopting ffctiv masurs, can human socity dvlop stadily and hav a bright futur.