Catherine Elizabeth Kendig

Homology is a natural kind concept, but one that has been notoriously elusive to pin down. There has been sustained debate over the nature of correspondence and the units of comparison. But this continued debate over its meaning has focused on defining homology rather than on its use in practice. The aim of this chapter is to concentrate on the practices of homologizing. I define “homologizing” to be a concept-in-use. Practices of homologizing are kinds of rule following, the satisfaction of which demarcates a category—that of being a homologue. Identifying, explaining, discovering, and understanding are exchanges that connect practice to concept through the performance of a rule by practitioners. These practices are constitutive of natural kinding activities. If homologizing is a kind of kinding, consideration of these practices of discovery, tracking, and identification not only clarifies the meaning, use, and progression of the concept of homology, but provides further understanding of the processes and progression of natural kinds and kinding practices in general.

Synthetic biology is a field of research that concentrates on the design, construction, and modification of new biomolecular parts and metabolic pathways using engineering techniques and computational models. By employing knowledge of operational pathways from engineering and mathematics such as circuits, oscillators, and digital logic gates, it uses these to understand, model, rewire, and reprogram biological networks and modules. Standard biological parts with known functions are catalogued in a number of registries (e.g. Massachusetts Institute of Technology Registry of Standard Biological Parts). Biological parts can then be selected from the catalogue and assembled in a variety of combinations to construct a system or pathway in a microbe. Through the innovative re-engineering of biological circuits and the optimization of certain metabolic pathways, biological modules can be designed to reprogram organisms to produce products or behaviors. Synthetic biology is what is known as a “platform technology”. That is, it generates highly transferrable theoretical models, engineering principles, and know-how that can be applied to create potential products in a wide variety of industries. Proponents suggest that applications of synthetic biology may be able to provide scientific and engineered solutions to a multitude of worldwide problems from health to energy. Synthetic biology research has already been successful in constructing microbial products which promise to offer cheaper pharmaceuticals such as the antimalarial synthetic drug artemisinin, engineered microbes capable of cleaning up oil spills, and the engineering of biosensors that can detect the presence of high concentrations of arsenic in drinking water. One of the potential benefits of synthetic biology research is in its application to biofuel production. It is this application which is the focus of this entry. The term “biofuel” has referred generally to all liquid fuels that are sourced from plant or plant byproducts and are used for energy necessary for transportation vehicles (Thompson 2012). Biofuels that are produced using synthetic biological techniques re-engineer microbes into biofuel factories are a subset of these.

Species concepts aim to define the species category. Many of these rely on defining species in terms of natural lineages and groupings. A dominant gene-centred metaconception has shaped notions of what constitutes both a natural lineage and a natural grouping. I suggest that relying on this metaconception provides an incomplete understanding of what constitute natural lineages and groupings. If we take seriously the role of epigenetic, behavioural, cultural, and ecological inheritance systems, rather than exclusively genetic inheritance, a broader notion of what constitutes a natural grouping or lineage may be required. I conclude by outlining an alternative metaconception that is a de-centred metaschema for species

In a very general sense, hybrid can be understood to be any organism that is the product of two (or more) organisms where each parent belongs to a different kind. For example; the offspring from two or more parent organisms, each belonging to a separate species (or genera), is called a “hybrid”. “Hybridity” refers to the phenomenal character of being a hybrid. And “hybridization ” refers to both natural and artificial processes of generating hybrids. These processes include mechanisms of selective cross-breeding and cross-fertilization of parents of different species for the purpose of producing hybrid offspring. In addition to these processes, “hybridization ” also refers to natural and artificial processes of whole genome duplication that result in the doubling or trebling of the sets of chromosomes of the organism. This entry provides an overview of the impact of hybridity on agriculture. It begins with an historical sketch that traces the early horticulturalists’ and naturalists’ investigations of hybrids. This starts with the observations of Thomas Fairchild and Georges-Louis Leclerc, Comte de Buffon; and leads to the explanation of its mechanism by Gregor Mendel, James Watson and Francis Crick, and Ernst Mayr; and the eventual manipulation of hybrids and hybridization by Barbara McClintock. Following this, the reader is introduced to a number of key terms and concepts in use within current research as well as highlighting diverse ethical concerns that center on hybridization. Recent research that attempts to ascertain the role of hybridization in adaptive change will be introduced. This will include research on the evolution of crop species, increased biodiversity, and the use of hybrids to manipulate phenotypically desirable traits in agricultural crops. The focus of the discussion is on a particularly significant type of naturally occurring hybridization, polyploidy hybridization. Polyploids are organisms which have more than two complete genomes in each cell. This kind of hybridization is ubiquitous among crop plants. The role of polyploidy in plant evolution and the affects of polyploidy on plants and animals will be reviewed. A critical discussion of its agricultural value in the production of fertile polyploid hybrids highlights key epistemological, ontological, and ethical issues. These are illuminated with reference to the distinct processes of artificial and natural hybridization. A survey of these different kinds of hybridization includes the ethical and economic impacts of hybridity on global nutrition, the environment, and considerations of some practical implications for the agricultural industry. Tracking the role of hybrids, the process of hybridization, and the current impacts of it for agriculture requires knowledge of the history of its early conceptualization, understanding, and use. This is the topic of the following section.