One's personality is both a composition and reflection, but if I have to choose one of them, I will choose reflection as the "self" is more important to me than "me". One's composition may change, walking across the cultural landscapes and climbing the social ladder but one's self is tied to one's reflections. The fun part is that reflections are not bound to "Time-Space" barriers ( it is not time-space) and respective mental constructs, which have grown so thick over ages, that they had reduced the image of humans to Sisyphus, rolling different sizes of boulders on hills of different heights.… As the name of this Blog indicates, knols are my perspectives on topics of interests, sweet/bitter experiences or just doodling :)
Tuesday, January 10, 2012
Testing Natural Selection
Let's have a look on commonly practicing definition and approach to natural selection. Futuyma (Douglas J. Futuyma, "Evolution" 2nd Edition, page; 283 ) writes,
"Natural Selection can exist only if different classes of entities differ in one or more features, or traits, that affect fitness..."
Defines fitness as,
"The fitness- often called the reproductive success - of a biological entity is its average per capita rate of increase in numbers. When we speak of natural selection among genotypes or organisms, the components of fitness generally consists of (1) the probability of survival to the various reproductive ages, (2) the average of number of offspring (e.g., eggs, seeds) produced via female function, and (3) the average number of offspring produced via male function. "Reproductive success" has the same components, since survival is a prerequisite for reproduction"....Sexual selection....
His actual definition of natural selection, "...Any consistent difference in fitness among phenotypically different classes of biological entities..."
If you carefully read from existence of natural selection to fitness and then definition of natural selection, it is all about three biological phenomenon, existence of variation and the survival and reproductive successes of organisms............very visible and easily measurable component... That is plus side but the problems come when we measure these components they become independent the abiotic factors that rule them.....
Molles (Manuel C. Molles Jr. "Ecology; concepts and application" 4th Edition, page 255) provides some examples that how environmental fluctuation control birth rate ( reproductive success) and death rate (survival),
"Sizes of populations fluctuate in terrestrial, as well as aquatic, environments. Some of the most variable terrestrial populations are found on the Galapagos Islands. The sizes of populations on these islands vary a great deal because they are subject to exceptional environmental fluctuations. Much of this fluctuation is produced by a large-scale climatic systems commonly called El Nino. El Nino warms the waters around Galapagos Islands and brings higher than average rainfall once or twice each decade. This increased rainfall stimulate germination and growth of plants. These plants produce abundance of seeds upon which Galapagos finches depend for food. In response to increased seed production, the size of finch populations can increase several folds in 1 year. However, these same populations are also exposed to periodic droughts. During droughts, which can be severe, both plants and finch population decline dramatically. Again whether in sea or on land, populations are dynamic."...........
Studies of decline and explosion of populations over long period of times is main way to study variation in population. Otherwise, measuring variation is making abstract notions out of the context interactions of biotic and abiotic interactions.....
To test this hypothesis we compare Natural Selection with an another hypothetical mechanism "Escaping competition". According to this mechanism, organisms try to be energy efficient and they tend to conserve their energy for main characteristics of life, like reproduction, growth, movements and socializations etc. (We use abbreviations like NC for natural selection and EC for escaping competition).
1. Artificial Selection:
NC: Natural selection is a biological process that is stretched for billions of years so human don't have a chance to observe it. But still there is artificial selection that is provoiding a good analogy to understant the natural selection. Human have domesticated cattles, fishes, dogs, horses, birds and have produced generations of these animals with desired traits over thousands of years. If human can change the animals and produce animals with desirable traits what about natural selection that works for billions of years?
EC: Two aspects of artificial selections is very important to note. Human have domesticated organisms to get energy (food, fuel), use for transportation (save energy) and amusements (escape competition/relax). Secondly, human didn't developed these desirable traits by competitions among these organisms but by separating them or making them escape out of competition.
Food for thought: If artificial selection is an analogy to natural selection then why human is much concerned about invasive species. Let local species compete with invasive species and desirable traits develop. But we human disagree and make laws and strong monitory policies to prevent local species from invasive species. Invasive species destroy habitate, introduce new diseases and have more tolerance to factors that local species are intolerant.
NC: On the page 84, Chapter IV, of the "On the Origin Of Species" Darwin writes, " When we see leaf-eating insects green, and bark-feeders mottled grey: the alpine ptarmigan white in winter, the red grouse the color of heather, and the black grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger. "
Camouflage is not limited to the same color as of your environments to escape predation but any tactics that save from predation could be entitled under camouflage. A unique example that Carl Sagan used is Samurai crab (Heikegani), a crab native to Japan that has a face of Samurai on its carapace. According to Carl Sagan this adaptation is the result of natural selection. As fisher men didn't eat the Samurai crab so adaptations favored against those of crabs without Samurai face.
EC: Organisms camouflage to escape competition. Competitions occur within species and camouflage is not to compete with each other but as Darwin says preserving them from danger. Escaping predation is a mechanism that evolution favors and this observation is consistent from Darwin, himself to our time.
NC: Organisms produce more offspring each generation that possibly could survive.
EC: From fishes which produce thousands of eggs in spawning season to lizards that lay tens of shell protected and to pouch mammals that give birth to a child and to human which also give birth children we see a decrease in mortality of offspring as organims become more evolved. In case of human in becomes more evident. In advanced countries there is less mortality rate in infants and fewer children per couple than backward countries where infant mortality is more with more children per couple. Hence evolution favors less offsprings.
External Link for further readings:
(This knol was part of my effort to rethink evolution and as is evident. not yet complete)