![]() Different species use different strategies to achieve these goals. Body plansĪll animals have evolved to survive and reproduce, and to do so they share common tasks that include the capture, ingestion, absorption, and distribution of food/nutrients the acquisition and distribution of oxygen for cellular respiration and the excretion of metabolic wastes and undigested materials 3. A glossary of terms and concepts used in the current review is included in the Appendix S2. Finally, we will use these data to draw conclusions about the evolutionary origins of the blood vascular system. Next, we will discuss concrete examples (and introduce primary ultrastructural data) from a spectrum of representative species, with a particular emphasis on invertebrates. We will begin with an overview of body plans in extant animals. By contrast, comparative biology provides a rich source of information that can be used to infer and reconstruct the evolutionary history of the cardiovascular system. Molecular phylogenetic analyses have yielded interesting, although limited insights into evolutionarily conserved mechanisms of heart development and tube formation. There is no trace of the cardiovascular system in the fossil record. The goal of this review is to explore the evolutionary origins of the blood vascular system and endothelium. When and why did the cardiovascular system evolve in the first place? Why are certain blood circulatory systems open, while others are closed? Why are some systems lined by endothelium, whereas others have no cell lining? These are important questions because they provide insights into the design constraints, path dependence, trade-offs, and selective pressures that underlie human physiology and vulnerability to disease. How does the heart generate force? How do blood vessels form during development? How do blood vessels and their endothelial lining function in health and how do they become dysfunctional in disease? By contrast, little attention is paid to the evolutionary mechanisms of the cardiovascular system. The field of cardiovascular biology is largely concerned with proximate mechanisms. Evolutionary explanations (‘when and why’) employ a combination of the fossil record, and comparative morphology and DNA sequences to describe the phylogenetic history of a trait and the fitness advantage that the trait provides at the level of a population or species 2. Proximate explanations (‘how’) employ traditional tools, including biochemistry, molecular biology, and cell biology to describe the anatomy, physiology, and ontogeny of a trait at the level of a modern-day organism. ![]() Finally, we emphasize that endothelial heterogeneity evolved as a core feature of the endothelium from the outset, reflecting its role in meeting the diverse needs of body tissues.Įvery biological trait requires both a proximate and evolutionary explanation (reviewed in 1). The endothelium evolved in an ancestral vertebrate some 540–510 million years ago to optimize flow dynamics and barrier function, and/or to localize immune and coagulation functions. Existing evidence suggests that the blood vascular system first appeared in an ancestor of the triploblasts over 600 million years ago, as a means to overcome the time-distance constraints of diffusion. In addition to drawing on the published literature, we provide primary ultrastructural data related to the lobster, earthworm, amphioxus, and hagfish. Here, we employ a comparative approach to review the phylogenetic history of the blood vascular system and endothelium. Comparatively little attention has been given to the evolutionary basis of the cardiovascular system. The field of vascular biology is focused primarily on proximate mechanisms in health and disease. Every biological trait requires both a proximate and evolutionary explanation. ![]()
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