The Theory of Evolution

The Theory of Evolution The theory of evolution  Is evolution JUST a theory? What is a theory?   A scientific theory is defined as “a scientifically accepted general principle supported by a substantial body of evidence offered to provide an explanation of observed facts and as a basis for future discussion or investigation.” The theory of evolution  Example – the theory of heredity Mendel and his peas – Laws of particulate inheritance, dominance, and recessiveness  The theory of evolution  Other scientific “theories” • The Heliocentric • • • hypothesis – Copernicus Atomic theory Quantum theory Theory of plate tectonics The theory of evolution   Thus evolution can be considered a fact that is explained by the theory of evolution. Two major hypotheses with respect to the theory of evolution. 1. 2. Descent, with modification, from common ancestor The cause of descent with modification is that natural selection sorts among variations. The evolution of evolutionary thought  Ancient Greeks – various ideas about the origins and diversity of life including • Empedocles of Acragas (in Sicily), proposed that the universe was composed of four basic elements -- earth, air, fire, and water. Jean-Baptiste Lamarck (1744-1829) •In 1809 Lamarck published the Philosophie Zoologique, where he proposed his hypothesis for evolutionary change. God Angels Kings/Queens Archbishops Dukes/Duchesses Bishops Marquises/Marchionesses Earls/Countesses Viscounts/Viscountesses Barons/Baronesses Abbots/Deacons Knights/Local Officials Ladies-in-Waiting Priests/Monks Squires Pages Messengers Merchants/Shopkeepers Tradesmen Yeomen Farmers Soldiers/Town Watch Household Servants Tennant Farmers Shephards/Herders Beggars Actors Thieves/Pirates Gypsies Animals Birds Worms Plants Rocks Lamarck  Lamarck believed that every species had originated individually by spontaneous generation at the bottom of the chain. Because species are continuously arising, the patterns we see now are the result of variation in the age of species.  Lamarck  Lamarck recognized that not all species fit into the chain of being, and he believed that adaptation caused some species to deviate from the chain. Species in different environments had different needs, and those organs and appendages that were used more often attracted “nervous fluid” which enlarged them.  Lamarckism  These changes acquired over a lifetime are inherited Laid foundation for Lamarck’s Theory of Inheritance of Acquired Characteristics  Key Features    Desire to change Use/Disuse Passing on of Acquired Characteristics • Ex. Long neck to giraffe offspring  Lamarck was on the right track, but had evolution happening much too fast / within short time frames Artificial Selection  Humans select traits of organisms • breeds and characteristics of dogs Artificial Selection  Agriculture • corn kernel characteristics Thomas Malthus (1766-1834)  An Essay on the Principle of Population (1798/1803) • Population growth is exponential • Food growth is limited/linear • Human demand for food will outstrip supply. Population growth Malthus • 1798: 950 million • Double every 25 years • 2000: 242 billion (actual: 6.1 billion) Food production Charles Darwin  Charles Darwin was born at Shrewsbury. His father was a doctor and his mother was the daughter of Josiah Wedgwood. Darwin first studied medicine at Edinburgh. It soon became clear to the family, and particularly to Charles, that he was not cut out for a medical career; he was transferred to Cambridge) there to train for the ministry. A Cambridge, befriended a biology professor (John Stevens Henslow) and his interest in zoology and geography grew.   Charles Darwin  In 1831, Charles accepted an invitation to join an expedition on the Beagle. Charles Darwin Charles’ ideas of descent with modification began to when he noticed that the finches from the Galapagos were so different from island to island.  Darwin’s Finches Beaks of Darwin’s Finches  Darwin collected a closely related group of 14 finch species in the Galapagos Islands. • All were similar except for beak characteristics. • Beak structures suggested to Darwin that they were shaped by evolution. • Based on the nature of available food supply Charles Darwin  He was additionally inspired by artificial selection and breeding programs in domestic animals. In the fall of 1838, formulated the Theory of Natural Selection  Charles Darwin   published his book The Origin of Species,. The book had two major themes 1.All living species have descended from a common ancestor 2.Theory of natural selection Darwin’s Evolution    Common Descent – radically different from Lamarck. Darwin was the first to propose that species had diverged from common ancestors. All of life could be viewed as a family tree. Darwin’s Evolution  Gradualness or Gradualism – Differences between organisms are the result of a large number of small “steps” or intermediate forms.  Puncuated Equlibria - changes occur by large leaps without intermediates. Somewhat controversial. Natural Selection  Darwin claimed that the ENVIRONMENT selected organisms with the best adaptive traits to survive and reproduce Traits were then passed on. Traits with no advantage died with owners and “died out”  Darwin’s Evolution   Natural selection – original hypothesis, independently determined by Alfred Wallace. Process by which the proportions of variant individuals within a species change over evolutionary time (generations). Beaks of Darwin’s Finches  Darwin collected a closely related group of 14 finch species in the Galapagos Islands. • All were similar except for beak characteristics. they were shaped by evolution. • Beak correspondence suggested to Darwin that • nature of available food supply Darwin’s Finches Peppered Moths and Industrialized Melanism  Until the mid-nineteenth century, peppered moths, Biston betularia, had predominately light-colored wings. • then, dark individuals became predominant • Industrial smog helped turn lichens on tree trunks dark. • Contrasting colors between trunk color and moth color led to different hunting (selection) by birds. Peppered Moths and Industrial Melanism Peppered Moths and Industrial Melanism  The second half of the twentieth century saw widespread implementation of pollution controls, thus trends reversed and light colored moths again dominated. • pollution created generally darker environment • Clean up created a generally lighter environment Selection Against Melanism Sources of New Species Step 1 – Founding Fathers/Mothers  Organisms move into an area These critters represent the founders  Sources of New Species 2. Physical Barriers to Mating (Gene Flow)  Physical barrier prevents gene flow between populations of a species • Archipelago hotbed of speciation Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon 3. Evolutionary Changes in the Gene Pool  Adaptation to the local environment exerts pressure on “traits” Most adapted organisms are SELECTED and so are their genes  4. Reproductive Isolation  Overtime, organisms develop new traits, behaviors, mating preferences Maybe that big-billed finch isn’t so attractive to the slim-billed finch. This is reproductive isolation Consider the Chihuahua and the St. Bernard as well    Reproductive Isolation Mating really isn’t Possible Sometimes … Getting the idea here? …  Adaptive Radiation  The idea that one species gives rise to MANY SPECIES Divergent Evolution = Adaptive Radiation Convergent Evolution  When “Mother Nature” causes two TOTALLY unrelated critters to evolve in similar ways, showing similar adaptations Directional Selection Directional Selection  Directional selection favors those individuals who have extreme variations in traits within a population.   Ex breeding of the greyhound dog. Early breeders were interested in dog with the greatest speed. They carefully selected from a group of hounds those who ran the fastest. From their offspring, the greyhound breeders again selected those dogs who ran the fastest. By continuing this selection for those dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph). The greyhound was originally used to hunt the fastest of game, fox and deer. Their bred dates to Egypt in 3BC.  Disruptive Selection Disruptive Selection  Disruptive selection, like directional selection, favors the extremes traits in a population. Disruptive selection differs in that sudden changes in the environment creates a sudden forces favoring that extreme. Example – a meteor hits the earth and critters with traits to survive are the only ones that do. A population may split into two distinct species when extreme forms have an advantages. This happens with certain forms of fish Surface dwellers (limnetic) – eat / live / reproduce at surface Bottom (benthic) dwellers –eat /live/reproduce on bottom Breeding doesn’t occur with sufficient frequency and the two forms evolve into separate species.       Three-Spine Stickleback Fish benthic (top) and limnetic (bottom) females Stabilizing Selection  favors the norm, common, average traits in a population Look at the Siberian Husky, a dog bred for working in the snow. The Siberian Husky is a medium dog, males weighing 16-27kg (35-60lbs). These dogs have strong pectoral and leg muscles, allowing it to move through dense snow. The Siberian Husky is well designed for working in the snow. If the Siberian Husky had heavier muscles, it would sink deeper into the snow, so they would move slower or would sink and get stuck in the snow.  Stabilizing Selection – reduces extremes The Case for Sickle Cell Anemia Sickle cell trait helps carrier survive malarial infection – an evolutionary advantage Speciation  A species is a group of organisms that are able to interbreed successfully, producing offspring who themselves can reproduce. When one group of organisms can no longer breed successfully with another group, then those two groups are considered to be different species. Speciation of Hawaiian Honeycreepers  New species • • Poor habitats on an isolated archipelago Start of geographic separation and, over time, speciation