Theories on Evolution.. Natural Selection..

Natural Selection is the process by which individual organisms with favorable traits are more likely to survive and reproduce than those with unfavorable traits. It works on the whole individual, but only the heritable component of a trait will be passed on to the offspring, with the result that favorable, heritable traits become more common in the next generation. Given enough time, this passive process results in adaptations and speciation by Charles Darwin.

Darwin's Finches
On his journey to Galapagos Island by Beagle, Darwin have found a specie on which he discovered the theory of Natural Selection.
Darwin was especially intrigued by one group of birds, the finches. The 13 species of Galapagos finches live nowhere else in the world. One island was found to contain several species. Each species of has a particular type of beak, which is suited to a certain kind of food. His observation of the finches were to become one of the strongest arguments for the role of natural selection in the origin of species - and today the finches are still considered to be a classic example of evolution.

Although the different genera and species of finches are identified mainly by differences in beak shape and feeding habits, they are basically alike.

The tree finch, found in the forest zone, has a short, thick beak and feeds mainly on insects taken from the bark of trees and also on seeds. The ground finch and warbler finch are found on all the islands. The cactus ground finch has a long slender beak and feeds on the flowers of the prickly pear. The large ground finch has a blunt, powerful beak for breaking open hard seeds. It also eats flowers, fruits and some insects. It can eat bigger seeds than the other ground finches. The warbler finch has a slender beak and feeds only on insects.

Darwin noticed that each species of finch had a different shape or size of beak. Bird's beaks are like tools - different ones are suited to different jobs. Beaks of different shapes are adapted to eating different kinds of food.

Darwin felt that it was too much of a coincidence to assume that all 13 species had been separately created to be so basically alike. He believed that it all started with one kind of finch arriving from the Soth American mainland and that evolution working over millions of years had resulted in the 13 species.

Summary of Natural Selection:

Thories on Evolution.. Catastrophism..

George Cuvier has also proposed a theory on evolution. It is the Catastrophism. This theory suggests that changes in the size of the earth's animal population was the outcome of a series of natural disasters or catastrophes, such as volcanic eruptions which killed fauna in a certain area.. Catastrophism would ultimately change the way the world viewed evolution, and would be the first of many later evolutionary theories of its kind.

Catastrophism is the theory that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope. The dominant paradigm of geology has been uniformitarianism (also sometimes described as gradualism), but recently a more inclusive and integrated view of geologic events has developed resulting in a gradual change in the scientific consensus.

Many think that the history of Catastrophism was from the Creationism view. It was believed that it was the cause of development and creation. One great example is the Great Flood which was told in the bible.

At the beginning of the nineteenth century, the great French geologist and naturalist Baron Georges Cuvier proposed what came to be known as the Catastrophe theory or Catastrophism. According to the theory, the abrupt faunal changes geologists saw in rock strata were the result of periodic devastations that wiped out all or most extant species, each successive period being repopulated with new kinds of animals and plants, by God's hand. [Charles] Lyell rejected so nonscientific a hypothesis (as did James Hutton before him), and replaced it with the notion that geological processes proceeded gradually - all geological processes. (Lewin, 1993)

Considering Catastrohism in various events:

• Scientists have been thinking whether the extinction of dinosaurs was due to the 10-km asteroid that struck the Earth 65 million years ago at the end of Cretaceous period. It wiped out 70% of species including the dinosaurs leaving a boundary called the K-T LIne.
  
• Modern theories also suggest that Earth's anomalously large moon was formed catastrophically. In a paper published in Icarus in 1975, Dr. William K. Hartmann and Dr. Donald R. Davis proposed that a stochastic catastrophic near-miss by a large planetesimal early in Earth's formation approximately 4.5 billion years ago blew out rocky debris, remelted Earth and formed the Moon, thus explaining the Moon's lesser density and lack of an iron core. See giant impact theory for a more detailed description.

Theories on Evolution.. Lamarckian theory..

This theory named, "Use and Disuse", was proposed by a scientist Jean Baptiste de Lamarck, real name:Jean-Baptiste Pierre Antoine de Monet Chevalier de Lamarck. It says that based on heritability of acquired characteristics, the once widely accepted idea that an organism can acquire characteristics during its lifetime and pass them on to its offspring.

It proposed that individual efforts during the lifetime of the organisms were the main mechanism driving species to adaptation, as they supposedly would acquire adaptative changes and pass them on to offspring. After publication of Charles Darwin's theory of natural selection, the importance of individual efforts in the generation of adaptation was considerably diminished. Later, Mendelian genetics supplanted the notion of inheritance of acquired traits, eventually leading to the development of the modern evolutionary synthesis, and the general abandonment of the Lamarckian theory of evolution in biology. In a wider context, Lamarckism is of use when examining the evolution of cultures and ideas, and is related to the theory of Memetics.

There are two basis of his theory:

1. Use and Disuse-wherein:

Use- certain structures could be developed when they are used
Disuse-certain structures are lost or becomes vestigial when they are not used

2. Inheritance of acquired traits- individuals acquire the traits of thir predecessors or ancestors

Because of these 2 ideas, Lamarck has developed two laws:
1. In every animal which has not passed its limit of development, a more frequent and continuous use of any organ gradually strenghtens, develops and enlarges that organ, and gives it a power proportional to the length of time it has been so used; while the permanent disuse organ imperceptibly weakens and deteriorates it, and progressively diminishes its functional capacity, until it finally disappears.
2. All the acquisitions or losses wrought by nature on individuals, through the influence of the environment in which their race has long been placed, and hence through the influence of the predominantly use and permanently disuse of any organ; all these are preserved by reproduction to the new individuals which arise, provided that the acquired modifications are common to both sexes, or at least to the individuals which produce the young.

Examples:

• It has been said that long ago giraffes have long necks but due to the scarcity of food (grass) , the giraffes stretched their necks, to reach the trees, thus lengthening it and developing it.. The offsprings will have slightly longer necks.
  
• The blacksmith is also a good example for this theory. Because of his work, the blacksmith's developing his muscles. His offspring will have the same muscular development when they mature.

But his theory was discredited by other experts for reasons:


In essence, a change in the environment brings about change in "needs" (besoins), resulting in change in behavior, bringing change in organ usage and development, bringing change in form over time — and thus the gradual transmutation of the species. While such a theory might explain the observed diversity of species and the first law is generally true, the main argument against Lamarckism is that experiments simply do not support the second law — purely "acquired traits" do not appear in any meaningful sense to be inherited. For example, a human child must learn how to catch a ball even though his or her parents learned the same feat when they were children.

(Though it is important to note that just because the skill of catching a ball can not be passed on from parent to child does not mean that we can rule out all other traits from being passed on in a Lamarckian fashion).

The argument that instinct in animals is evidence for hereditary knowledge is generally regarded within science as false. Such behaviours are more probably passed on through a mechanism called the Baldwin effect. Lamarck’s theories gained initial acceptance because the mechanisms of inheritance were not elucidated until later in the 19th Century, after Lamarck's death.

Several historians have argued that Lamarck's name is linked somewhat unfairly to the theory that has come to bear his name, and that Lamarck deserves credit for being an influential early proponent of the concept of biological evolution, far more than for the mechanism of evolution, in which he simply followed the accepted wisdom of his time. Lamarck died 30 years before the first publication of Charles Darwin's Origin of Species. As science historian Stephen Jay Gould has noted, if Lamarck had been aware of Darwin's proposed mechanism of natural selection, there is no reason to assume he would not have accepted it as a more likely alternative to his "own" mechanism. Note also that Darwin, like Lamarck, lacked a plausible alternative mechanism of inheritance - the particulate nature of inheritance was only to be observed by Gregor Mendel somewhat later, published in 1866. Its importance, although Darwin cited Mendel's paper, was not recognised until the Modern evolutionary synthesis in the early 1900s. An important point in its favour at the time was that Lamarck's theory contained a mechanism describing how variation is maintained, which Darwin’s own theory lacked.

Many experts have been thinking of considering Lamarck's theory as a basis of cultural evolution.
(source:
http://en.wikipedia.org/wiki/Lamarckian)

Theories on Evolution.. Scale of Nature..

Way back many years ago, even leading back to the time of Aristotle, several scientists gave studied and proposed their theory on evolution.

One of the first scientists who have studied evolution was Aristotle. Hr proposed a theory on evolution named the "Scale of Nature."

Scale of Nature- this theory of Aristotle's states that species are arranged in a ladder-like order where the inanimate matter(non-living things) is on the lowest step while the human was on the highest.

Chain of Being- another influential philosopher at the time of Darwin, nature exists in an orderly ladder or "Great Chain of Being." At the bottom of the ladder is inanimate matter (i.e. dirt and rocks). At the top of the latter are immaterial, spiritual beings like the gods. Half way up the ladder are humans--half material and half immaterial spirit.

Introduction to Evolution

Evolution is the genetic change in population or species over generations; all the changes that transform life on Earth; the heritable changes that have produced Earth's diversity of organisms.

There are three important elements in evolution:

1. descent- it means that species come from a common ancestor


2. time- it takes time for species to evolve


3. development-there are developments as species evolve