Abstract
An understanding of the factors behind the evolution of multicellularity is one of today’s frontiers in evolutionary biology. This is because multicellular organisms are made of one subset of cells with the capacity to transmit genes to the next generation (germline cells) and another subset responsible for maintaining the functionality of the organism, but incapable of transmitting genes to the next generation (somatic cells). The question arises: why do somatic cells sacrifice their lives for the sake of germline cells? How is germ/soma separation maintained? One conventional answer refers to inclusive fitness theory, according to which somatic cells sacrifice themselves altruistically, because in so doing they enhance the transmission of their genes by virtue of their genetic relatedness to germline cells. In the present article we will argue that this explanation ignores the key role of policing mechanisms in maintaining the germ/soma divide. Based on the pervasiveness of the latter, we argue that the role of altruistic mechanisms in the evolution of multicellularity is limited and that our understanding of this evolution must be enriched through the consideration of coercion mechanisms.
Highlights
The evolution of multicellularity is, according to Maynard Smith and Szathmary (1995), one of the major transitions in evolution, i.e., one of those events in the history of life in which certain units lose their capacity to reproduce independently as a result of their formation of higher-level units capable of reproduction as a whole
In the case we study in this article, policing mechanisms involve the biological structures that actively control the excessive reproduction of somatic cells in order to guarantee the long-term survival of a multicellular organism and the transmission of germline cells
Which of the two scenarios mentioned in the third section better explains the existence of somatic cells? Based on what we have shown in the last two sections, we think that the second scenario describes the situation of somatic cells much more accurately: somatic cells are placed in the role of units which are not in control of their inclusive fitness, coerced to sacrifice themselves; in other words, despite the genetic relatedness between somatic and germline cells, the mechanisms holding them together to form a multicellular organism are based not on altruism, but on strict policing
Summary
The evolution of multicellularity is, according to Maynard Smith and Szathmary (1995), one of the major transitions in evolution, i.e., one of those events in the history of life in which certain units lose their capacity to reproduce independently as a result of their formation of higher-level units capable of reproduction as a whole. In the case of the evolution of multicellularity, independently reproducing cells, as they evolved into multicellular individuals, lost their independent capacity for reproduction. Multicellular individuals have the capacity to reproduce themselves and to control the reproduction of the cells of which they are composed. These cells comprise two main subsets: somatic cells, whose reproductive regime is controlled and limited to the ontogeny of Adrian Stencel and Javier Suárez declare that their contributions to the article have been equal. Why did certain formerly reproducing entities give up their reproductive potential to aid the reproductive abilities of other elements within a higher-level
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