Browsing by Author "Wang, Steve C"

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    A quantitative formulation of biology's first law.
    (Evolution; international journal of organic evolution, 2019-06) McShea, Daniel W; Wang, Steve C; Brandon, Robert N
    The zero-force evolutionary law (ZFEL) states that in evolutionary systems, in the absence of forces or constraints, diversity and complexity tend to increase. The reason is that diversity and complexity are both variance measures, and variances tend to increase spontaneously as random events accumulate. Here, we use random-walk models to quantify the ZFEL expectation, producing equations that give the probabilities of diversity or complexity increasing as a function of time, and that give the expected magnitude of the increase. We produce two sets of equations, one for the case in which variation occurs in discrete steps, the other for the case in which variation is continuous. The equations provide a way to decompose actual trajectories of diversity or complexity into two components, the portion due to the ZFEL and a remainder due to selection and constraint. Application of the equations is demonstrated using real and hypothetical data.
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    Hierarchical complexity and the size limits of life.
    (Proceedings. Biological sciences, 2017-06) Heim, Noel A; Payne, Jonathan L; Finnegan, Seth; Knope, Matthew L; Kowalewski, Michał; Lyons, S Kathleen; McShea, Daniel W; Novack-Gottshall, Philip M; Smith, Felisa A; Wang, Steve C
    Over the past 3.8 billion years, the maximum size of life has increased by approximately 18 orders of magnitude. Much of this increase is associated with two major evolutionary innovations: the evolution of eukaryotes from prokaryotic cells approximately 1.9 billion years ago (Ga), and multicellular life diversifying from unicellular ancestors approximately 0.6 Ga. However, the quantitative relationship between organismal size and structural complexity remains poorly documented. We assessed this relationship using a comprehensive dataset that includes organismal size and level of biological complexity for 11 172 extant genera. We find that the distributions of sizes within complexity levels are unimodal, whereas the aggregate distribution is multimodal. Moreover, both the mean size and the range of size occupied increases with each additional level of complexity. Increases in size range are non-symmetric: the maximum organismal size increases more than the minimum. The majority of the observed increase in organismal size over the history of life on the Earth is accounted for by two discrete jumps in complexity rather than evolutionary trends within levels of complexity. Our results provide quantitative support for an evolutionary expansion away from a minimal size constraint and suggest a fundamental rescaling of the constraints on minimal and maximal size as biological complexity increases.