Second: The Theory of Development and Evolution
On November 24,1859, Charles Darwin published his famous book On the Origin of Species By Means of Natural Selection, or, the Preservation of Favored Races in the Struggle for Life. In this book, he presented a theory stating that organisms on the earth (plants and animals) evolved, and did not come into existence suddenly or at once.
Although at the time Darwin did not have enough fossils to support his theory, he presented evidence that he obtained from an observation and research of hybridization and domestication during his famous global expedition on the HMS Beagle, and from the observations and research of other biologists. Most of Darwin’s evidence came from observation, comparative anatomy, and research on the lineage of modern organisms. However, scientiﬁc evidence for evolution continued to accumulate after Darwin through research, aided by technological advancements in the study of fossils, comparative anatomy, and genetics.
Darwin, as well as the evolutionary biologists who came after him, concluded that the combination of variation between individuals (due to variation in their genetic plans, for instance), the process of selection carried out by their natural surroundings, and heredity, results in evolution of life suitable for that environment.
If the reader understands the meaning of variations in genetic plans and nature’s preservation or selection of the favored races, then they will clearly see that evolution is inevitable, and that fossil evidence as proof of evolution is unnecessary.
Simply stated, whenever we have variation, selection, and heredity, we inevitably have evolution. Variation exists, and there is no doubt that it is present among individuals of the same species. Selection also inevitably exists, because it is an intrinsic part of nature, its demands, and the environmental changes that constantly occur, such as declining water levels, droughts, rising or dropping temperatures, or the introduction of a new predator or prey. And as long as breeding and reproduction occurs, heredity is inevitable as well. So evolution was inevitable in the past, just as it is in the present, and will be in the future, since all of its required components have and still do exist.
Therefore, the issue is not debatable, because it is as clear as the earth’s spin. In addition to this, there is evidence that has accumulated from comparative anatomy, fossils, and genetics that conﬁrms evolution, though evolution is obvious, even in the lineage of modern organisms.
Evolution Of Compound Organ Such As Eye, Ear And Nose
Therefore, evolution occurs whenever there is variation, heredity due to reproduction, and natural selection of the ﬁttest. For example, if we take the evolution of compound organs such as the eye, ear, and nose, the ﬁrst evolutionary step would be the evolution of a sensory cell in a primitive, multi-cellular animal. These cells would then multiply in later generations, due to the fact that there is variation caused by genetic mutation that provides for this multiplication. If these sensory cells provide beneﬁt and energy for the animal by helping it to elude enemies and acquire food, and the energy provided exceeds the cost, then animals with this trait will be more capable of surviving, and will be selected by the natural environment. With this, selection of these sensory cells takes place. So in this way, whenever the evolutionary step is of more beneﬁt than cost to the animal, it will be preserved.
After specialized sensory cells multiply through evolutionary steps due to variation and selection, a group of cells that sense light becomes available, and another group that senses chemicals or smell also becomes available, and so on. When a group of cells that senses light exists in the animal, and variation is also present, the environment selects the most favorable cells to progress toward the optimal state. So a concave shape is favored because it senses light better, as is a lens that concentrates light and makes the image clearer, and so forth.
When suitable improvement mutations are available, the animal favors (not through consciously favoring, but in accordance with the law of evolution that I have described) a system that combines and organizes the work of sensory cells with different functions as a group, rather than individually, because that makes it better able to survive. If mutation provides such a system, or provides the connection of such a system between the sensory cells and the organization of their work, then the system will be preserved. This represents the primitive nervous system, which we can say is the basis for the brain.
And this is how the sensory cells evolve to become an eye, a nose, etc. In general, it is a matter of economics for the animal: if the trait acquired through genetic mutation helps the animal to obtain food and increases its ability to acquire two units of energy while the energy expenditure of putting this trait into operation is one unit, then this trait will beneﬁt the animal, and will usually be preserved.
On the other hand, when the energy expenditure of operating the trait exceeds the beneﬁt (and using the above example, the energy expenditure would be three units), then the l, and it will be eliminated. Elimination in this instance does not mean that an individual animal eliminates the trait, but rather it is eliminated by the entire species, meaning that animals that acquire this trait that is more harmful than beneﬁcial will perish, because they won’t be capable of surviving or competing with their peers.
There is a difference of opinion regarding the path taken by evolution, and there are several theories to explain its course. These theories disagree about the speed of evolution and whether it always proceeds very slowly, or whether its speed is discretely variable or continuously variable. There is also the theory of extreme genetic mutation that has been abandoned, for the most part. This theory states that a compound organ comes into existence directly and at one time through a single genetic mutation.