Somatic cellular differentiation plays a critical role in the transition from unicellular to multicellular life, but the evolution of its genetic basis remains poorly understood. By definition somatic cells do not reproduce to pass on genes and so constitute an extreme form of altruistic behavior. The volvocine green algae provide an excellent model system to study the evolution of multicellularity and somatic differentiation. In Volvox carteri, somatic cell differentiation is controlled by the regA gene, which is part of a tandem duplication of genes known as the reg cluster. While previous work found the reg cluster in divergent Volvox species, its origin and distribution in the broader group of volvocine algae has not been known. Here we show that the reg cluster is present in many species without somatic cells, and determine that the genetic basis for soma arose before the phenotype at the origin of the family Volvocaceae approximately 200 million years ago. We hypothesize the ancestral function was involved in regulating reproduction in response to stress and that this function was later co-opted to produce soma. Determining that the reg cluster was co-opted to control somatic cell development provides insight into how cellular differentiation, and with it greater levels of complexity and individuality, evolves.

While numerous criteria have been proposed in definitions of biological individuality, it is not clear whether these criteria reflect the evolutionary processes that underlie transitions in individuality. We consider the evolution of individuality during the transition from unicellular to multicellular life. We assume that "individuality" (however it is defined) has changed in the volvocine green algae lineage during the transition from single cells, to simple multicellular colonies with four to one hundred cells, to more complex multicellular organisms with thousands of differentiated cells. We map traits associated with the various proposed individuality criteria onto volvocine algae species thought to be similar to ancestral forms arising during this transition in individuality. We find that the fulfillment of some criteria, such as genetic homogeneity and genetic uniqueness, do not change across species, while traits underpinning other aspects of individuality, including degrees of integration, group-level fitness and adaptation, and group indivisibility, change dramatically. We observe that different kinds of individuals likely exist at different levels of organization (cell and group) in the same species of algae. Future research should focus on the causes and consequences of variation in individuality.

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The damaging outcomes of racist ideologies continue to influence all aspects of society. This in spite of the fact that at their core these ideologies rely on a fundamentally false assumption: that biologically there are different races among humans. The source of this fallacy is pseudoscience and historical prejudice, and yet even scientists and medical professionals continue to apply misconceptions about biological race when performing research or practicing medicine. Scientific educators are in a unique position to dismantle the central damaging assumption, and here we provide a straightforward approach that educators can employ for engaging in this conversation. It is organized around four questions that build sequentially and integrate the latest science with a history of the topic: How did the myth of biological subcategories of humans become ingrained as a scientific concept? How has scientists’ approach to taxonomy changed since Linnaeus’s first human classifications? What does biology now tell us about variation within the human species? Why is it critical to debunk this myth? We provide answers with which scientific educators can re-center the conversation around historical and scientific facts, while highlighting how misapplication of the evidence harms the integrity of science as a field.

The evolutionary transition from single-celled to multicellular individuality requires organismal fitness to shift from the cell level to a cell group. This reorganization of fitness occurs by re-allocating the two components of fitness, survival and reproduction, between two specialized cell types in the multicellular group: soma and germ, respectively. How does the genetic basis for such fitness reorganization evolve? One possible mechanism is the co-option of life history genes present in the unicellular ancestors of a multicellular lineage. For instance, single-celled organisms must regulate their investment in survival and reproduction in response to environmental changes, particularly decreasing reproduction to ensure survival under stress. Such stress response life history genes can provide the genetic basis for the evolution of cellular differentiation in multicellular lineages. The regA-like gene family in the volvocine green algal lineage provides an excellent model system to study how this co-option can occur. We discuss the origin and evolution of the volvocine regA-like gene family, including regA—the gene that controls somatic cell development in the model organism Volvox carteri. We hypothesize that the co-option of life history trade-off genes is a general mechanism involved in the transition to multicellular individuality, making volvocine algae and the regA-like family a useful template for similar investigations in other lineages.