Directional Selection Is One of Three Types of Natural Selection

Directional Selection Is One of Three Types of Natural Selection Directional selection  is one type of  natural selection  in which the  phenotype  (the observable characteristics) of the species tends toward one extreme rather the mean phenotype or the opposite extreme phenotype. Directional selection is one of three widely studied types of natural selection, in addition  to  stabilizing selection  and  disruptive selection. In stabilizing selection, the extreme phenotypes gradually reduce in number in favor of the mean phenotype, while in disruptive selection, the mean phenotype shrinks in favor of extremes in either direction.   Conditions Leading to Directional Selection The directional selection phenomenon is usually seen in environments that have changed over time. Changes in weather, climate, or food availability can lead to directional selection. In a very timely example connected to climate change, sockeye salmon have recently been observed shifting the timing of their spawn run in Alaska, likely due to rising water temperatures.   In a  statistical analysis of natural selection, directional selection shows a population bell curve for a particular trait that shifts either further left or further right. However, unlike  stabilizing selection, the height of the bell curve does not change. There are far fewer average individuals in a  population that has undergone directional selection. Human interaction can also speed up directional selection. For example, human hunters or fishermen pursuing quarry most often kill the bigger individuals of the population for their meat or other large ornamental or useful parts. Over time, this causes the population to skew toward the smaller individuals. A directional selection bell curve for size will show a shift to the left in this example of directional selection. Animal predators can also create directional selection. Because slower individuals in a prey population are more likely to be killed and eaten, directional selection will gradually skew the population toward faster individuals. A bell curve plotting species size will skew toward the right when documenting this form of directional selection.   Examples As one of the common forms of natural selection, there are plentiful examples of directional selection that have studied and documented. Some well-known cases:   Charles Darwin  studied what later became known as directional selection while he was in the  Galapagos Islands. He observed that the beak length of the Galapagos  finches  changed over time due to available food sources. When there was a lack of insects to eat, finches with larger and deeper beaks survived because the beak structure was useful for cracking seeds. Over time, as insects became more plentiful, directional selection began to favor  finches  with smaller and longer beaks that were more useful for catching insects.Fossil records show that black bears in Europe decreased in size during periods between continental glacial coverage during the ice ages, but increased in size during the glacial period. This was likely because larger individual enjoyed an advantage in conditions of limited  food supplies and  extreme cold.  In 18th and 19th century England peppered moths who had been predominantly white in order to blend in with light colored trees began t o evolve into a predominantly dark species in order to blend in with an environment that was becoming increasingly covered with soot from Industrial Revolution factories.

15 Groovy, Awesome, Swell and Cool Words

15 Groovy, Awesome, Swell and Cool Words 15 Groovy, Awesome, Swell and Cool Words 15 Groovy, Awesome, Swell and Cool Words By Michael Whats your favorite word of compliment or admiration? How do you express approval? These are important questions for each generation of young people, who want their vocabulary to distinguish them from previous generations. Its not fool-proof: a slang expression of approval is often fashionable in one place or time but not another, and may even coming back into fashion later. A word that is fashionable in one school might be considered outdated in another. Perhaps the longest reigning compliment is Cool! after an unusual run of popularity among several generations of young people, it remains fashionable in 2019. But in the last century, dozens of similar words have come in and out of fashion. ace Meant top quality, as in the highest playing card in a standard deck. A flying ace in World War I meant a pilot who had shot down five or more planes in combat. A student who gets an A on a test can say, I aced it! But once upon a time, it was used as a positive exclamation: Ace! meant Great! awesome typical of GenX youth (those born roughly between 1961 and 1981), but also used by American preteens in 2019. Example: This popcorn is awesome! One of several contemporary uses of a stronger word in a weaker sense, awesome originally means producing terror, then full of awe or awe: The volcano erupted in an awesome shower of fire. More recently, it has been used for anything thats moderately interesting (such as rocks, socks and clocks in the Lego Movie song Everything is Awesome.) Perhaps this usage expresses a hope for a life thats more than moderately interesting, or else, youthful enthusiasm. bad An example of contrarianism in youth slang (bad means good), but still with the original connotation of rough or evil. That is, a girl would not say, Oooh, thats a bad bouquet of flowers! Thank you! Ill put them in a vase right now. bully One of the favorite adjectives of U.S. President Teddy Roosevelt, meaning grand or excellent. Used in this sense in Great Britain by 1680 and revived in popularity America around 1844 (Bully for you!). Its meaning changed from the Middle Dutch boele, meaning lover or boyfriend, later probably used similarly to Ooh, your boele is really bad! I like him! to the current sense of someone who is cruel to those weaker than himself. But when Roosevelt was President (1901 to 1909), it was probably as popular as cool is today, and meant approximately the same thing. cool This word has also kept its Old English meaning of low temperature. Someone with a cool head is not hot-headed or easily angered he has control of his passions. But a dispassionate person might also lack compassion for others, an implication of cool in the 1957 musical West Side Story. In the 1940s, tenor saxophonist Lester Young popularized the word as an expression of calm approval and satisfaction. If you ask teens in the Teens if they need anything, maybe something to eat or drink, they may respond, No, Im cool or No, Im good. It has been spelled kewl, but thats now dated or ironic. crack Used in the phrase crack shot, an accurate marksman, but it means good or skilled in general. Samuel Johnsons dictionary definition involved quickness or smartness. epic Frequently used by young gamers but common among many young male Americans, meaning very cool and exciting, Originally used for important events or great objects worthy of long works of heroic poetry such as the Iliad, the Odyssey, the Aeneid, Beowulf, and Paradise Lost. Political campaigners like to refer to the epic accomplishments of their candidate, if any, the last time her or she was in office, if ever. groovy Popular in the 1960s among surfers and hippies. It even became the title of a Los Angeles television show in 1967, live from the beach in Santa Monica. But it originated in the Jazz Era of the 1920s, from the phrase in the groove, referring to the groove on vinyl records. If you were in the groove, you were part of the latest music scene. gucci From the high-quality clothing line, used by YouTuber Matt Smith to mean high quality or good. When a former enemy becomes your friend, you can say about your relationship, Its all gucci. In a 1999 magazine interview in Harpers Bazaar, singer Lenny Kravitz calls his bedroom very Gucci. hep According to the Merriam-Webster Dictionary, the word hep was first used in 1862 to mark the cadence of a march, like this: HEP 2 3 4 HEP 2 3 4 The words Left left left-right-left served the same purpose and also made it clear which foot you should put forward when. By 1900, it had already begun to mean trendy. decades before it was adopted by beatniks and hippies. hip Originally spelled hep, this word referred to the most current-conscious residents of the 1960s. Someone who was hip knew all the latest jargon, wore the latest fashions, and understood the latest ideas. To say Im hip with that meant I know what youre talking about and I agree. So a hippie at the time was someone who was very hip. Of course, being trendy is a moving target the word was first used in this sense in 1904, and trends have changed substantially since then. mod Beginning about 1958, the mod youth culture was typified by young sharp-dressing, scooter-riding working class Londoners, but spread around the world. So in the early 1960s, if something was mod, it was trendy. Long after mod stopped being a common compliment, an American TV series called The Mod Squad debuted in 1968 and ran until 1973. Its young undercover detective stars were more hip than mod, using solid and groovy as their compliments. The word was revived effectively later according to a middle-aged GenXer, That word was so 80s. sick Another example of contrarianism in youth slang. Being ill is disagreeable, but something that is sick is attractive. In other words, calling a skateboard sick is an expression of admiration. On Mark McCrindles list of the most annoying youth phrases in Australia, fully sick is number 2. swell By 1786, a swell was a dandy, a fashionable person with a swollen sense of self-importance. But it became an exclamation of admiration. In the musical The Music Man, set in 1912, Professor Harold Hill warns parents against sinister influences on their sons: Are certain words creeping into his conversation? Words like like swell! But it was too late: by 1930, expressions such as Thats just swell! had become common in the United States. wild The theme song of The Patty Duke Show (1963-1966) says about the two main characters (both played by Patty Duke) What a wild duet! Perhaps a 1960s reaction to the staid 1950s, where wild behavior was not acceptable. Want to improve your English in five minutes a day? Get a subscription and start receiving our writing tips and exercises daily! Keep learning! Browse the Vocabulary category, check our popular posts, or choose a related post below:Comparative Forms of Adjectives40 Synonyms for â€Å"Different†Types of Plots