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Fig. 2 | Biology Direct

Fig. 2

From: Was the evolutionary road towards adaptive immunity paved with endothelium?

Fig. 2

Schematic illustration of evolutionary forces designated as ‘pressure’ or ‘release’. Whereas previous theories have attempted to identify a selective pressure that would ‘drive’ the evolution of the AIS, we argue that the physiological context of vertebrates provided the release from evolutionary constraint that allowed the effective implementation of an AIS. A shift towards a more active lifestyle imposed the need for a higher metabolic scope. This includes the development of specialised cells for the storage of energy-rich molecules (adipocytes – an innovation unique to vertebrates [7]) to buffer against sudden supply or demand shocks and a high-output vascular system typical of vertebrates. The higher metabolic scope would allow for the implementation of a costly AIS, whereas vascular parameters decrease the total cost of ownership of an AIS and promote AIS functionality

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