TheWeismann barrier, proposed byAugust Weismann, is the strict distinction between the "immortal" germ cell lineages producing gametes and "disposable" somatic cells in animals (but not plants), in contrast toCharles Darwin's proposedpangenesis mechanism for inheritance.[1][2]
In more precise terminology, hereditary information is copied only fromgermline cells tosomatic cells. This means that new information from somatic mutation is not passed on to the germline. Thisbarrier concept implies that somatic mutations are not inherited.[3][4]
Weismann set out the concept in his 1892 book ″Das Keimplasma: eine Theorie der Vererbung″ (German forTheGerm Plasm: a theory of inheritance).[5] The use of this theory, commonly in the context of thegerm plasm theory of the late 19th century, before the development of better-based and more sophisticated concepts of genetics in the early 20th century, is sometimes referred to asWeismannism.[6] Some authors distinguishWeismannist development (eitherpreformistic orepigenetic) that in which there is a distinct germline, fromsomatic embryogenesis.[7] This type of development is correlated with theevolution of death of the somatic line.
The Weismann barrier was of great importance in its day and among other influences it effectively banished certainLamarckian concepts: in particular, it would make Lamarckian inheritance from changes to the body (the soma) difficult or impossible.[8] It remains important, but has however required qualification in the light of modern understanding ofhorizontal gene transfer and some other genetic and histological developments.[9]
The Russian biologist and historianZhores A. Medvedev, reviewing Weismann's theory a century later, considered that the accuracy ofgenome replicative and other synthetic systems alone could not explain the "immortal"germ cell lineages proposed by Weismann. Rather Medvedev thought that known features of the biochemistry and genetics ofsexual reproduction indicated the presence of unique information maintenance and restoration processes at the different stages ofgametogenesis. In particular, Medvedev considered that the most important opportunities for information maintenance ofgerm cells are created byrecombination during meiosis andDNA repair; he saw these as processes within the germ cells that were capable of restoring the integrity ofDNA andchromosomes from the types of damage that caused irreversible ageing insomatic cells.[10]
Basal animals such as sponges (Porifera) and corals (Anthozoa) contain multipotent stem cell lineages, that give rise to both somatic and reproductive cells. The Weismann barrier appears to be of a more recent evolutionary origin among animals.[11]
In plants, genetic changes in somatic lines can and do result in genetic changes in the germ lines, because the germ cells are produced by somatic cell lineages (vegetativemeristems), which may be old enough (many years) to have accumulated multiple mutations since seed germination, some of them subject to natural selection.[12] It is noteworthy in this context that, generally speaking, adult, reproducing plants tend to produce many more offspring in number than animal organisms.