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trands and rates of evolution
The document discusses several trends and rates of evolution, including Dollo's law of irreversibility, Cope's law of body size increase over generations, and Gause's exclusion principle of ecological niche overlap. It also covers Bergman's rule relating body size and temperature, techniques for examining evolutionary rates like DNA analysis, and the hypotheses of gradual vs punctuated change to explain rates of evolution. Resources on these topics are listed at the end.
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trands and rates of evolution
- 2. Qasim Ali BS 7th Trendsand Rates of Evolution Department of Zoology Kohat University of Science and Technology, Kohat 26000, Khyber Pakhtunkhwa, Pakistan
- 3. Outline Trends ofEvolution Dollo’s Law of Irreversibility Cope's law Gause's rules / Exclusion Principle Bergman’s rule Rate of Evolutionary Change Technique that used to examine the rate of evolutionary Two hypotheses to explain the rate of evolutionary change Punctuated equilibrium hypotheses Gradual change hypothesis Resources
- 4. Trends of Evolution An evolutionary trend can be defined as a directional change in a set of character states, resulting in a significant change through time. Dollo’s Law of Irreversibility first proposed in 1890 by French-born Belgian engineer and paleontologist Louis Dollo (1857-1931) and further elaborated into the status of a proposed law in his 1893 article “The Law of Evolution”.
- 5. Dollo stated“that an organism cannot return, even partially, to a previous state already realized in its ancestral series.” Today, this is known as Dollo’s law of irreversibility. Accordingly, most evolutionists believe that evolution simply proceeds forward. For organisms with a membrane-bound nucleus, they hold that the operation of natural processes is sufficient to account for the diversity of the organisms’ genes and traits. They believe there is no specific course that evolution is ordained to follow, but once it proceeds, there is essentially no “reverse evolution.” French-born Belgian engineer and paleontologist Louis Dollo (1857-1931), the eponym of Dollo's law
- 6. Cope's law Evolutionarytrends towards an increase in body size are common in the fossil record. For example, the Eocene ancestors of modern horses were about the size of a dog. Since then, in the lineages showing the largest increases, horses have evolved to become as much as 10 times heavier. Figure: over the last sixty million years, the average weight of horses has increased ten times.
- 7. The advantages ofbeing big: improved ability to capture prey (lions) or to escape predation (sauropod dinosaurs, elephants); greater reproductive success (sexual selection); increased intelligence (brain size relates to body size); expanded size range of acceptable food (giraffes, elephants); decreased annual mortality (as a result of the above); extended individual longevity (life span relates broadly to body size); increased heat retention per unit volume (Bergmann's rule) There are also disadvantages with large size particularly the large animals require a great deal of food, like Elephants have to migrate huge distances merely to find enough fodder. In addition, large animals size is clearly exposed to predators than a related lineage of smaller animals.
- 8. Gause's rules /Exclusion Principle The exclusion principle says that ‘‘if two species have almost completely overlapping niches they cannot continue to coexist.’’ One of the two species will outcompete the other and persist. The other will go locally extinct. The classic experiments were by Gause using two species of Paramecium Paramecium caudatum and Paramecium aurelia. When cultured separately in yeast medium. P. aurelia was found to have faster rate of increase than P. caudatum. When both species were added to the same culture vessel. P.aurelia dominated the mixture and eventually P.caudatum died out.
- 10. Bergman’s rule Effectof temperature on size of an animal. The birds & mammals of colder areas are larger in size as compared to their equivalents in warmer area, again to reduce their surface area: volume ratio. There is some evidence to support Bergmann's Rule: for example, polar bears are much larger than spectacled bears, which live closer to the equator, and a number of animals do develop size variation both within species and in closely related species which can be correlated to geographic location. Bergmann's Rule has also been used to explain the typically heavier body types of people from Arctic regions when compared to equatorial peoples. e.g : 1m long penguin in Antartica & 0.5m long in Galapagos island
- 12. Rate of EvolutionaryChange Rate of evolution is a measurement of the rate of genotype change of species and organisms over a period. Evolutionary change can be estimated by examining fossils and species that are related to each other. Technique used to examine the rate of evolutionary change: DNA analysis is technology that involves identifying the percentage of similarity between samples of DNA from two related organisms under study. The greater the similarity the more have chances from a common ancestor. The information that is obtained in this manner is compared to information obtained from other sources such as the fossil records and studies in comparative anatomy.
- 13. Two hypotheses toexplain the rate of evolutionary change Gradualism and punctuated equilibrium hypothesis That are two ways in which the evolution of a species can occur. A species can evolve by only one of these, or by both. Scientists think that species with a shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution evolved mostly by gradualism. Gradualism is selection and variation that happens more gradually. Over a short period of time it is hard to notice. Small variations that fit an organism slightly better to its environment are selected for: a few more individuals with more of the helpful trait survive, and a few more with less of the helpful trait die. Very gradually, over a long time, the population changes. Change is slow, constant.
- 14. Punctuated equilibriumhypothesis There is a period of very little change, and then one or a few huge changes occur, often through mutations in the genes of a few individuals. Mutations are random changes in the DNA that are not inherited from the previous generation, but are passed on to generations that follow. Though mutations are often harmful, the mutations that result in punctuated equilibrium are very helpful to the individuals in their environments. Because these mutations are so different and so helpful to the survival of those that have them, the proportion of individuals in the population who have the mutation/trait and those who don't changes a lot over a very short period of time.
- 15. RESOURCES Gould, StephenJay. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press, 2002. Milligan, B.G. Estimating Evolutionary Rates for Discrete Characters. Clarendon Press; Oxford, England, 1994. Ridley, Mark. Evolution. Cambridge, MA: Blackwell Scientific Publications, 1993. Dollo, L. (1893). “The Law of Evolution” (“Les lois de l’evolution”), Bulletin de la Societe beige de geologie, de plaentologie, et d'hydrologie, 7:164-67. Dollo, quoted in "Evolution: Ammonites Indicate Reversal," in Nature, March 21, 1970. Louis Dollo – Wikipedia. Brooks, Daniel R. and Wilson, E.O. (1986). Evolution as Entropy: Toward a Unified theory of Biology. (1988, 2nd ed.). University of Chicago Press.