Testing Evolutionary Brain Size Change in Bats
In his classic text on the evolution of the brain in vertebrates, Jerison (1973) demonstrated with numerous examples that brains have increased in size over time in most mammal lineages. He thus confirmed a general trend that had been progressively recognized since the time of Marsh (1874). More recent studies have confirmed Jerison’s findings for primates (Martin, 1990), cetaceans (Marino et al., 2004) and carnivores (Finarelli & Flynn, 2007). It was originally thought that the development in brain size was related to body surface area (Jerison, 1973), but then it was shown that brain size may be correlated to maternal metabolic turnover instead (Martin, 1981). This alternative interpretation was proposed because of the high energetic cost of brain tissue. However, brain size may vary by a factor of five relative to body weight. This wide range of variation cannot be explained by variation in adult basal metabolic rate alone, so the brain size of mammals must be affected by other things such as the early developmental period. Recognition of this led to formulation of the Maternal Energy Hypothesis (Martin, 1996). Larger brains may therefore be due to increase in the resources the mother provides to the developing offspring, according to the mode of reproduction. However, on an evolutionary scale, brain size usually increases due to new adaptations and generally beneficial characteristics.
This interpretation was challenged by Safi et al. (2005) with respect to bats. These authors proposed that evolution of the brain in different bat lineages had involved reduction as well as enlargement in brain size. The suggestion that bat brains may become smaller in evolution was spe...
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...h as bat brains, brain volume is approximately equal to brain mass. The body mass and brain mass of the modern bat species are known from data collected by Karen Isler (2009). For both modern bats and fossil bats, the brain mass to body mass ratio can be calculated for the different species and compared.
Preliminary analysis indicates that the data generated and collected from this past summer show that bat brain sizes in the family Rhinolophidae have increased, not decreased, in size over time. The question remains, though, what characteristics did bats gain to make them need a larger brain? Safi et al. had proposed the idea of energetic cost in favor of an evolutionary movement toward smaller bat brain sizes, so what counteracts this? This is an important question that can be explored by studying more fossil bat brains, which are quite rare.
http://www.med.nyu.edu/content?chunklID=90869>. Gerrard, David E., and Alan L. Grant. Principles of Animal Growth and Development. Dubuque, IA: Kendall/Hunt Pub., 2006. Print.
...f we are to know anything about our own evolutionary history, we must begin by looking where it counts. If we discover that the methods we are using and the things we are looking at do not tell us what we want to know then we must reassess those methods and attempt to find ones that do tell us what we want to know. From looking at bone growth and development we have learned that the features we observe do not tell us what we thought they did. We must find a different way to study the traits that have bearing on the course of adaptive trends. By studying brain growth and organization we have a new place to look. Positional analysis provides a way for us to actually sort out the traits that are applicable and meaningful, such as how the processes of bone growth reflect brain growth. This allows us to continually check ourselves and keep from making the same mistakes.
Darwin: A Norton Critical Edition, Second Edition ; ed. by Philip Appleman; copyright 1979, 1970 by W.W. Norton & Company, Inc.
Long standing arguments against the theory of natural selection stem from the occurrence of incipient structures and complex traits in organisms despite the seemingly stochastic nature of mutations. Many complex adaptations observed in nature today are thought to have arisen from less complex ones with simpler functions, therefore these characters are thought to have been “pre-adapted.” In order to go from a simple to a complex structures there must have been a transitional phase, where the two structures function simultaneously or where the new function is assumed without interfering with the old function. These structures are termed incipient or incomplete, and given what we know to be true of natural selection and the theory of evolution it becomes hard to reconcile the idea that natural selection continued to favor these structures despite the lack of selective value. Incipient structures are thought to be neither sufficiently large enough not elaborate enough to perform an adaptive function and thus it also becomes difficult to understand how larger complex characters arise. A discussion of morphological and developmental genetics explains that these structures have been performing useful functions since their simple origins, therefore being selectively favored while at the same time evolving to become large enough to accumulate new more complex functions. Modification of pre-existing genes and regulatory circuits in early development has been extensively studied in metazoans, Hox genes and the development of complex structures such as eyes, limbs and appendages. Phenotypic variation is therefore generated via the modification of existing genes, regulatory processes and developmental processes and this variation is acted o...
The second of Tinbergen’s questions Phylogeny looks at the evolutionary explanations of development, as opposed to just how behaviour has adapted, including mutations in response to environmental changes. Some of these mutations remain in species even after necessity has gone, and can influence future characteristics of that species. The third of Tinbergen’s questions looks at Causation,...
Experiments performed on animals and humans are showing that the brain has evolved to shape itself according to what it e...
The origin of modern day whales, a mystery that has puzzled paleontologists for years, may have just been solved with the discovery of an ankle bone. This discovery might sound simple and unimportant, but the bones of these ancient animals hold many unanswered questions and provide solid proof of origin and behavior. The relationship between whales and other animals has proven to be difficult because whales are warm-blooded, like humans, yet they live in the sea. The fact that they are warm-blooded suggests that they are related to some type of land animal. However, the questions of exactly which animal, and how whales evolved from land to water, have remained unanswered until now.
Encephalization is a relationship between brain mass and total body mass of an organism. Biologists often use the encephalization quotient (EQ) value, the relative size of a brain given an organism’s body mass, to gauge species’ intelligence. Humans have an average EQ of 7.44 and this is the highest EQ value of all known species (Kinser 2012). Chimpanzees and elephants, which are considered to be among the most intelligent species, have EQ values of 2.49 and 1.87, respectively. Bottlenose dolphins have the second highest EQ values of any species with an average EQ of 5.31 (Kinser 2012). Orcas have an EQ value of about 2.5 and larger cetaceans have ...
Gould, Edwin, George McKay, and David Kirshner. Encyclopedia of Mammals. San Francisco, CA: Fog City, 2003. Print.
World Archaeology, 31:3:329-350. Mitani, J.C. et al 1996 Sexual Dimorphism, the Operational Sex Ratio, and the Intensity of Male Competition in Polygamous Primates. The American Naturalist, 147:6:966-980. Rogers, Alan R. and Arindam Mukherjee 1992 Quantitative Genetics of Sexual Dimorphism in Human Body Size.
Marzluff, J., Angell, T. & Elliot, B. (2013, May. - Jun.). Birds: Brains over brawn. Audubon, 115(3), 40-41.
One of the most important and pivotal physical and biological adaptations that separate humans from other mammals is habitual bipedalism. According to Darwin, as restated by Daniel Lieberman, “It was bipedalism rather than big brains, language, or tool use that first set th...
The members of the Homo genus possess a combination of unique features that distinguish them from other related species. At the time that each respective species was alive, they were able to walk upright on two legs, use their large brains for the benefit of their species, and could thrive in many geographically and climatically diverse areas of the world. One of the most mysterious quandaries in science is how the lineage of the Homo genus became so different from their primate relatives. Bipedalism, brain size, and location diversity all have a common link that may explain this difference – dietary evolution allowed humans to adapt to their surroundings, and in turn, become a more advanced species. The Homo diet evolved in relation to food availability and nutritional necessity. With the ability to maintain a proper diet, the species of the Homo genus were able to flourish and advance toward the development of modern Homo sapiens.
This paper will look at what evidence there is that may imply that some, if not all, vertebrate animals may have the capacity for conscious thinking. Cognition, for example is something that animals may require in order to adapt to their changing environments so quickly. Cognition is an animal’s ability to make a decision by evaluating or processing current information based on some representation of prior experience (Kamil in Pepperberg 127). Some animal studies, such as Franci...
For years studies and observations have been made on the relationship between body size and physical orientation of an animal. In 1847 Carl Bergmann was one of the first to do observations with this phenomenon (Dictionary of Theories 2002). Bergmann noticed that warm-blooded animals living at climates high in latitude are bigger in size than those living in climates of lower latitudes (Dictionary of Theories 2002). Research has shown there is a correlation of surface area to volume in animals that are located in different parts of the globe. Animals living in a cooler climate have a larger volume, but decreased surface area to retain as much body heat as possible. The inverse is true for animals living in warmer regions; these animals have a smaller volume and larger surface area to allow the body to cool efficiently (McNab 1971). Bergmann’s rule has brought valuable insight into the study of character traits and how we identify where animals originated. One example that I came across is with the Andean passerine bird, a study was done in 1991 by G. R. Graves. He noticed the size of ...