The germline is constituted by all cells that have the potential to transmit their genetic information to the next generation. The germline can be considered as a defined sequence of genetic, cellular, and developmental processes recurring in each generation in order to ensure the continuity of a species-specific reproduction program. Although basic mechanisms of germline development in mammals are highly conserved, relatively slight yet relevant modifications of germline development evolved in different groups of mammals to adapt the entire process to the specific requirements of and conditions in each species. This review highlights selected aspects that illustrate germline adaptations and characteristics in primates mainly in comparison to the mouse, which is the best investigated mammalian model organism in reproductive biology. The germline is constituted by all cells that have the potential to submit their genetic information to the next generation. The cycle of the germline in mammals is characterized by the recurring sequence of (1) fertilization, i.e., fusion of 2 haploid gametes, resulting in (2) a diploid phase of early embryonic development, which leads to (3) the specification and separation of germ cells (primordial germ cells; PGCs) from somatic cells, followed by (4) several rounds of mitotic divisions of the germ cells. Then (5) the germ cells enter meiosis, i.e., the genetic reduction division, resulting in (6) haploid cells forming gametes again. Fusion of the haploid male and the female gametes completes the cycle of the germline and begins the next generation ( Fig. 1 ). This sequence of events occurs in all mammals. However, different species exhibit specific adaptations and characteristics of 1 or more phases of the cycle of the germline. Remarkably, the cycle of the germline is an extremely robust process that works "endlessly". On the other hand, certain dynamics of the germline is essential for evolution since only modifications of the germline cells can lead to (genetically or epigenetically) inherited traits possibly resulting in better-adapted offspring and, hence, supporting species diversion. In light of these conflicting goals, namely germline stability and genome dynamics, some selected characteristic features of male germ cell development in pri- A new generation is initiated by the formation of a zygote, i.e., the fertilized oocyte. In the morula-stage embryo, the individual cells (blastomeres) are not yet specified. They are all potential progenitor cells of the prospective germ cells. The blastocyst consists of 2 clearly distinguishable cell populations: the inner cell mass cells (highlighted by red arrows) and the outer cell layer, i.e., the trophoblast. The germ cells develop from the inner cell mass cells. In the implantation embryo the first specified germ cells, called PGCs, occur. In the somite-stage embryos they are frequently located in the epithelium of the developing hind gut (red arrows). In the fetus, most PGCs have entered the forming gonad. The magnifie...