Which evolutionary innovation has been the most influential, and why? Grace Mortiz Upper Sixth
Throughout the history of animal life, environmental and ecological shifts have resulted in both small and large scale evolutionary diversifications. Examples include the invasion of land around 400 million years ago, giving way to new habitats and niches for many organisms (Erwin 2015). Mass extinctions, namely the one at the end of the Permian period which wiped out 95% of earth’s species, have also created new evolutionary opportunities (Lumen Learning n.d.). These events have been the origins of evolutionary innovations, which are defined as ‘traits that produce something novel compared to before’ (Dall’Olio 2012). In this article the evolution of warmbloodedness, the eye and the mitochondria will be discussed, in order to conclude which of these innovations may have been the most influential. In today’s world, the only warm-blooded animals, otherwise known as endotherms, are mammals and birds. The origins of warm-bloodedness is a controversial issue because anatomical features that were thought to be linked to warm bloodedness have also been found in cold-blooded reptiles. These features include turbinates, which are bones inside the nose or snout, which increase the distance that air has to travel to get into the body. This allows it to warm up on the way in. What we do know is that the development of a warm-blooded metabolism allowed ancestors of mammals and birds to survive the giant mass extinction at the end of the Permian around 252 million years ago (Rey n.d.).
A recent study that looked at the ratios of oxygen isotopes in fossils has suggested that ancestors of mammals may have acquired warm-bloodedness between 259-252 million years ago, earlier than previously thought. This in turn suggests that climate may have been the selection pressure that triggered the evolution of warm-bloodedness (Rey n.d.). There are other theories as to why warmbloodedness arose in our ancestors - for example, as a result of pathogens. In order to achieve ‘fever’ like high body temperatures that boosts the effectiveness of some immune cells, cold-blooded animals, or ‘ectotherms’ would have had to sit in the sun for extended periods, as they cannot maintain a high body temperature
internally (Smithsonian Tropical Research Institute 2019). Endotherms can maintain a constant high body temperature internally, which allows the immune system to deal with pathogens more effectively. Logan, a Tupper Fellow at the Smithsonian Tropical Research Institute (STRI), suggests that “by keeping their bodies warm at nearly all times, mammals and birds effectively prime their immune systems to withstand virulent pathogens, and this may be part of the reason the extremely costly strategy of endothermy evolved in the first place.” Perhaps therefore, warm-bloodedness holds critical advantages over ectothermy, making it a particularly influential innovation. Endotherms are not restricted by thermal variation and can enter new habitats and niches. However ectotherms may be sensitive to environmental fluctuations, and in searching for warm spots to initiate ‘fever’, they may struggle to find food, to mate, and may be more exposed to predators. (Smithsonian Tropical Research Institute 2019).
Endotherms are not restricted by thermal variation and can enter new habitats and niches.
Smithsonian Tropical Research Institute
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Schwab (2018) describes the existence of eyes as “so basic to our profession that we do not consider how and why vision appeared or evolved on earth at all”. He believes that “sight is an evolutionary gift” but it was not an “ineluctable” one. Through the process of evolution by natural selection, different types of ‘eyes’ have emerged over
