Anatomy, Evolution, and Homologous Structures

Anatomy, Evolution, and Homologous Structures If youve ever wondered why a human hand and a monkeys paw look similar, then you already know something about homologous structures. People who study anatomy define these structures as a body part of one species that closely resembles that of another. But you dont need to be a scientist to understand that recognizing homologous structures can be useful not just for comparison, but for classifying and organizing the many different kinds of animal life on the planet. Scientists say these similarities are evidence that life on earth shares a common ancient ancestor from which many or all other species have evolved over time. Evidence of this common ancestry can be seen in the structure and development of these homologous structures, even if their functions are different. Examples of Organisms The more closely organisms are related, the more similar the homologous structures are. Many mammals, for example, have similar limb structures. The flipper of a whale, the wing of a bat, and the leg of a cat are all very similar to the human arm, with a large upper arm bone (the humerus in humans) and a lower part made of two bones, a larger bone on one side (the radius in humans) and a smaller bone on the other side (the ulna). These species also have a collection of smaller bones in the wrist area (called carpal bones in humans) that lead into the fingers or phalanges. Even though the bone structure may be very similar, function varies widely. Homologous limbs can be used for flying, swimming, walking, or everything humans do with their arms. These functions evolved through natural selection over millions of years. Homology and Evolution When Swedish botanist  Carolus Linnaeus was formulating his system of taxonomy to name and categorize organisms in the 1700s, how the species looked was the determining factor of the group in which the species was placed. As time passed and technology advanced, homologous structures became more important in deciding the final placement on the phylogenetic tree of life. Linnaeuss taxonomy system places species into broad categories. The major categories from general to specific are kingdom,  phylum,  class,  order,  family,  genus, and  species. As technology evolved, allowing scientists to study life at the genetic level, these categories have been updated to include domain, the broadest category  in the taxonomic  hierarchy. Organisms are grouped primarily according to differences in ribosomal  RNA  structure. Scientific Advances These changes in technology have altered the way scientists categorize species. For example, whales were once classified as fish because they live in the water and have flippers. After it was discovered that those flippers contained homologous structures to human legs and arms, they were moved to a part of the tree more closely related to humans. Further genetic research has demonstrated that whales may be closely related to hippos. Bats were originally thought to be closely related to birds and insects. Everything with wings was put into the same branch of the phylogenetic tree. After more research and the discovery of homologous structures, it became apparent that not all wings are the same. Even though they have the same function- to make the organism able to get airborne- they are structurally very different. While the bat wing resembles the human arm in structure, the bird wing is very different, as is the insect wing. Scientists realized that bats are more closely related to humans than to birds or insects and moved them to a corresponding branch on the phylogenetic tree of life. While the evidence of homologous structures has long been known, it has just recently been widely accepted as evidence of evolution. Not until the latter half of the 20th century, when it became possible to analyze and compare DNA, could researchers reaffirm the evolutionary relatedness of species with homologous structures.

The Concept of Gemeinschaft and Gesellschaft

The Concept of Gemeinschaft and Gesellschaft Gemeinschaft and Gesellschaft  are German words that mean community and society respectively. Introduced in classical social theory, they are used to discuss the different kinds of social ties that exist in small, rural, traditional societies versus large-scale, modern, industrial ones. Gemeinschaft and Gesellschaft in Sociology Early German sociologist Ferdinand  Tà ¶nnies introduced the concepts of  Gemeinschaft (Gay-mine-shaft)  and  Gesellschaft  (Gay-zel-shaft) in his 1887 book  Gemeinschaft und Gesellschaft. Tà ¶nnies presented these as analytic concepts which he found useful for studying the differences between the kinds of rural, peasant societies that were being replaced across Europe by modern, industrial ones.  Following this, Max Weber further developed these concepts as ideal types in his book  Economy and Society  (1921)  and in his essay Class, Status, and Party. For Weber, they were useful as ideal types for tracking and studying the changes in societies, social structure, and social order over time. The Personal and Moral Nature of Social Ties Within a  Gemeinschaft   According to  Tà ¶nnies,  Gemeinschaft, or community, is comprised of  personal social ties and in-person interactions that are defined by traditional social rules and result in an overall cooperative social organization. The values and beliefs common to a  Ã¢â‚¬â€¹Gemeinschaft  are organized around appreciation for personal ties, and because of this, social interactions are personal in nature.  Tà ¶nnies believed that these kinds of interactions and social ties were driven by emotions and sentiments (Wesenwille), by a sense of moral obligation to others, and were common to rural, peasant, small-scale, homogenous societies.  When Weber wrote about these terms in  Economy and Society, he suggested that a  Gemeinschaft  is produced by the subjective feeling that is tied to affect and tradition. The Rational and Efficient Nature of Social Ties Within a  Gesellschaft On the other hand,  Gesellschaft, or society, is comprised of impersonal and indirect social ties and interactions that are not necessarily carried out face-to-face (they can be carried out via telegram, telephone, in written form, through a chain of command, etc.). The ties and interactions that characterize a  Gesellschaft  are guided by formal values and beliefs that are directed by rationality and efficiency, as well as by economic, political, and self-interests. While social interaction is guided by  Wesenwille, or seemingly naturally occurring emotions  in a  Gemeinschaft, in a  Gesellschaft,  Kà ¼rwille, or rational will, guides it. This kind of social organization is common to large-scale, modern, industrial, and cosmopolitan societies that are structured around large organizations of government and private enterprise, both of which often take the form of bureaucracies. Organizations and the social order as a whole are organized by a complex division of labor, roles, and tasks. As Weber explained, such a form of social order is the result of rational agreement by mutual consent, meaning members of society agree to participate and abide the given rules, norms, and practices because rationality tells them that they benefit by doing so. Tà ¶nnies observed that the traditional bonds of family, kinship, and religion that provide the basis for social ties, values, and interactions in a  Gemeinschaft  are displaced by scientific rationality and self-interest in a  Gesellschaft. While social relations are cooperative in a  Gemeinschaft  it is more common to find competition in a  Gesellschaft. Gemeinschaft  and  Gesellschaft  in Modern Times While it is true that one can observe distinctly different types of social organizations prior to and after the industrial age, and when comparing rural versus urban environments, its important to recognize that  Gemeinschaft  and  Gesellschaft are ideal types. This means that though they are useful conceptual tools for seeing and understanding how society works, they are rarely if ever observed exactly as they are defined, nor are they mutually exclusive. Instead, when you look at the social world around you, you are likely to see both forms of social order present. You may find that you are part of communities in which social ties and social interaction are guided by a sense of traditional and moral responsibility while simultaneously living within a complex, post-industrial society.