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On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life establishes that species, over many generations, experience a vast amount of different stimuli and conditions which may lead to variations within organisms. These, necessarily inheritable variations inevitably establish a kind of hierarchy within nature; the most well adapted variations within a particular environment during a given time being those that can most easily or efficiently reproduce and survive. This in no way implies that there is a definite hierarchy of species in which all species are moving toward a fixed ‘best possible scenario’, simply that species tend to adapt to become well suited for the environment of the areas they occupy under the current conditions of that environment. Any change in environment may cause this ‘best adapted’ species to become ill-equipped to survive in the area compared to another variation which may lead to its eventual replacement. The survivability of a species is in no way static and constantly changes with its environment and availability of scarce resources. Since those variants which are best adapted survive and reproduce more often, they are more likely to pass on their inheritable variability to offspring and thus, over many generations, will make up the overwhelming majority of a particular species; often, if not always, leading to the extinction of its parent species.
Variability is attributed to the conditions of the reproductive organs, possibly the most environmentally influenced organs of species, prior to mating. This is shown in domesticated plants and animals, which, under domesticated environments, no matter how healthy, unlike their natural counterparts, seldom reproduce or appear to have greatly impotent reproductive organs. However, domesticated animals that do reproduce often are selected, and have been selected, or bred, by humans throughout time based on traits through artificial selection. Because these traits can be selected for based on phenotype (physical characteristics), and because this method has been used successfully by many breeders, beneficial traits must be hereditary. Since this hereditary difference cannot be established by the species that do not mate under confinement, environment and reproductive organs must be vital to variability and thus vital to the theory of speciation by natural selection. If a variation is not heritable, it will not be passed onto future generations and thus can not lead to accumulative variability over time and would be impossible to select for or against. Thus traits must be heritable in order for selection to occur. If beneficial heritable traits can be selected for in domesticated (artificial) selection, it must be concluded that they can also be selected for naturally, or, through natural selection with the most physically equipped organisms prospering.
Variations and species are often hard to decipher for they both share very similar characteristics. However, it has been shown that variants often occupy a far smaller geographical range than its relative species. This holds true by definition: if a variant appears more frequently and has a larger range than its relative species then this variant will be the species and the group of organisms occupying the smaller range will be considered the variant, not the species. Of course, taking this logic of mere range and appearance constituting species, it becomes unclear which physical traits truly determine which organisms are which species and whether or not they are species or just mere varieties. Thus, it holds, that the only way to determine which organisms are species and which are variants of that species is by observing their intermediate links which are seldom observed due to an incomplete historical record of organisms.
However, it is observed that within genera, species tend to accumulate in groups with variants; each group of species with its variants differing significantly from the next. Within these groups, the different variants tend to occupy only small ranges because they are closely related, thus have similar environmental needs, thus undergo strong competition with each other. It must follow, that since all the similar variants of that species share similar needs, the ones which are the best adapted to fulfill those needs will survive, passing on their hereditarily beneficial traits to their offspring, and the rest, incapable of fulfilling such needs, will perish. The species, or most common variant within that population, is thus hypothesized to be the best adapted for that given time; however, with environments in constant influx, a better adapted variant can arise at any time and quickly replace the existing species. This occurring and reoccurring over several millennia will lead to such large phenotypic differences in these variants that they can eventually be considered a new species entirely different from it parent species. However, this kind of hindsight may be deceptive; in this example it is apparent that this variant became a species became a variant became a species and so on, but as stated earlier, this becomes harder to apply to current species because the historical record of organisms is quite incomplete and because variants, although usually only a select few prosper, usually appear several at a time. This may lead to the conclusion that an organism existing today is a variant because it occupies a smaller range when it may actually be the parent species becoming extinct (this occurs relatively fast when compared to the age of the Earth) as the up and coming variant defeats its parent species in the struggle for existence.
Although the above case must be true some of the time, (species rarely, if ever, become extinct in a day) it by no means, must be true in all the time. Most often, variability in nature is due to many variations of the parent species existing simultaneously due to environmental changes or random chance; more than one prospering, perhaps, because migration or geographic separation keeps them from directly competing (genetic drift). An argument against transmutation is that species and their ancestral links are not usually seen simultaneously in nature. However, this is to be expected with speciation through natural selection for if a species and its variants are struggling for the same resources and a variant becomes more capable of obtaining these resources, it is expected that the parent species will quickly be replaced by its variant as resources become scarce. Therefore, it follows that through natural selection it is quite queer, even contradictory, to assume that a parent species and its better adapted variants can live together while competing for the same limited resources. However, variety as it is observed today makes far more sense when explained through natural selection than through creation. Larger genera appear to have more variance than smaller genera which, under natural selection, is explained by more variants occurring over a larger range with numerous different environmental influences selecting for variable traits. Independent creation leads to no conclusions as to why larger genera ought to have more variants.
Hybridization occurs when two organisms mate and produce usually sterile offspring. Many have concluded that this occurs in order to prevent confusion between all the living organisms. However, when a species and very closely allied variant reproduce, it often greatly heightens fertility. If this were not true, natural selection could never take place. Thus, hybridization must not be a major determining factor in the variation of species, for the impotence of hybrid offspring greatly selects against such hybridization occurring and prospering. For example, given that hybrids are generally sterile and crosses with varieties are generally more fertile, it is safe to assume that all breeds of dog did not occur with the mating of different breeds with one another, but rather, that different breeds of dog slowly emerged over time as variants became more able to produce other variants and so on.
Some of the variation seen in the natural world today may be part of a much different kind of selection termed sexual selection. Sexual selection, partly like natural selection, is selected for based on the species’ ability to reproduce and make offspring. However, sexual selection is the result of organisms directly competing with one another for mates by means that may not always be economically valuable for an organism. For example, a peacock having a very luxuriant tail with many feathers will attract more mates, making it sexually selected for; however, this large, cumbersome tail may make it more vulnerable to attack by predators, thus not a good means to prosper by view of natural selection. Sexual selection may function in a way that has large negative influences on an organism in relation to its predator while having large benefits in its relationship to other members of the same species. Therefore, on the grand scheme of nature, sexual selection and natural selection may appear to conflict, but both lead to the same means: more reproduction, thus more offspring to inherit the traits of the parents, thus more variants within nature.
Instinct accounting for variability, in some cases, seems to produce effects that are counter productive in the process of natural selection. Many species of ants survive by producing a certain kind of offspring which cannot reproduce and whose job, solely, is to work for the good of the community. The hypothesis is that given that these kinds of ants are completely sterile, there is no way that there existence can be selected for given the means of natural selection. However, it must be accounted for that the mere existence of these worker ants improves the likelihood that the rest of the nest will survive. Given this information, it must be concluded that ants producing less of these offspring will have a smaller chance of survival when competing over the resources they must have to share with other ants in the area. Therefore, colonies with more variants producing larger amounts of sterile worker ants will be the most successful, thus the sterile worker ants are indirectly selected for through their parents. Extremely large amounts of sterile workers will be selected against, for too many workers to feed without producing offspring will have a negative affect on the survivability of the nest; this is why nests are not made up entirely of workers. Furthermore, hive bees making the most geometrically productive hives have to expend far less energy to produce large quantities of honey and thus have higher survivability than their neighboring hives, and ants that most effectively use slaves have higher survivability than those that do not. Thus, it appears as though variation in natural instinct may arise in ways very similar, if not the same as, natural selection.
To provide evidence for speciation and gradual change over time, geologists turn to the ground to find fossil structures of species that are extinct, yet closely related to those organisms which exist in the natural world today, in hopes of finding the missing or unobservable ancestral links. Remains of organisms which no longer exist in the modern world have been found in strata in countries all around the world. Such findings are difficult to explain under the independent creation theory without incorporating some kind of transitional theory in which species are not immutable fixed forms. However, it is philosophically harder to understand how a perfect creator can independently make several imperfect beings that would eventually die or be forced to change, than to imagine organisms imperfectly changing through adaptation only to survive their harsh surroundings better than their closely allied variants. However, the fossil record is grossly incomplete, making turning to it as an authority quite difficult. Where one might expect, given that the earth is billions of years old with species constantly changing at slow rates, that countless varieties ought to be found in strata, in actuality, very few are found. This occurs for several reasons: soft organisms cannot be preserved, shells and bones deteriorate where no sediment accumulates, fossils buried in sediment will deteriorate from rain water if their sediment moves to the surface, geologists have relatively little idea how to compare species relative to each other when sediment may be barren during some intervals in certain parts of the world while lush with ancient life forms in others, and many fossils preserved in the sediment of the sea deteriorate as muddy waters erode them. A key process in fossil formation is when sediment slowly accumulates, the rate of subsidence being roughly equal to the amount of sediment, thus keeping the water shallow enough to support life. Large amounts of organisms will supply enough remains to be buried in the sediment to resist erosion when the sediment reaches the level of the land and shallow water will not erode the bones or remains before they can be buried in the sediment.
Although the geological record may show that many years passed between one sediment formation and another, geologists are in no way certain how long it takes any one species to change into another. Also, usually subsidence occurs with large scale climatic change, during which times many aquatic life forms are suspected to have migrated to other areas. Thus, it must be concluded that certain forms of fish found around the world may have only lived in their area of fossilization for an extremely small amount of time. The same logic applies to land animals; all the intermediate links of land animals may not be found in the fossil record because fossils tend to only accumulate with large changes in climate. Because of this quick change in climate, it is hypothesized that either the organisms would die off before they had a chance to show variance (climate change must be assumed to occur much quicker than variation in species) or migrate away to a more convenient climate; however, away from where they would become fossilized. Only a variant given large amounts of time to overcome its parent species in the struggle for resources will eventually widen its range enough to migrate back to where its parent form originated. Thus, geologists ought to expect only to find a few intermediate links for it is preposterous to assume an organism will have enough time to adapt to its surroundings if it stays in the same area with quickly changing conditions in environment and climate.
The best way to establish the family line of a certain species is if graduating fossils are found in extremely thick deposits of the same sediment, but even then it is hard to tell whether the two remains are separate species or just variations since there is no scientifically determined way of deciphering species based on physical forms. However, when comparing two distinct yet consecutive stages of the same species, it has been observed that the wider the gap, the more dissimilar the organisms are, and vice versa. Also, when observing the fossil record, it is found that the same organism is never found to reappear after several generations. This is not hard to grasp given that organisms are in no way connected to any kind of predetermined evolutionary path; they simply vary by random chance and adapt to their environments through natural selection. Even if the environmental conditions return to their original state, there is no reason to assume an organism must in some way revert back to its parent form, simply that is must adapt to its environment by means of natural selection. Given that this variant is not the same as the organism it originated from, there is no reason to assume it must adapt in the same way. Although the fact of natural selection could practically be made a scientific certainty with a complete fossil record, given the method in which geological strata are formed, it is highly unlikely to suspect such a record will ever be found or exist. However, it must be understood that not being able to directly observe every variant of every species throughout history in the fossil record in no way makes the view of species changing into new species over time an absurd statement.
The most striking accounts for the theory of natural selection are those of geographical distribution, rudimentary forms, morphology, and embryology. The geographical distribution of organisms shows that animals divided by large geographical barriers tend to vary most significantly. For example, most marsupials live only in the Australian continent. This is because they did not have to compete with the mammals of the mainland and had a much different environment with which to adapt. The same is seen on the island country of New Zealand where many birds have lost their ability to fly with no aboriginal land animals to hunt them. It is difficult to explain why most islands are completely devoid of land mammals using creation theory for there is no reason why mammals would not be and flightless birds would be independently created on islands; however, natural selection explains this merely by explaining that mammals do not live on islands because they have had no means to journey to them and birds lost their flight because several variants no longer needed the use of their wings. Given that the birds no longer use or need their wings, it is hard to explain why a perfect designer would make anything an organism does not need; however, natural selection explains the existence or rudimentary organs like the wings of an ostrich or the legs of a snake: through disuse, the organism’s survival is no longer contingent upon the organ and thus is vulnerable to variation through natural selection. If there is a single best form of wing, arm, hoof, flipper, etc… it seems highly unlikely that they will all be based on the same basic structural form; however, all these forms, from the fin of a dolphin to the hand of a human all have the same basic bone structure, all consisting of the same bones. This shows that perhaps the forms seen in the natural world are all modified versions of the same appendage shared by a common ancestor. Lastly, the embryos of many species all appear the same because organisms are not generally selected for or against in such preliminary states in their development. Thus, looking at embryos is much like taking a glance into the past, seeing from what similar structure all organisms must have originated.
Natural selection offers a scientifically verifiable case for the reason and persistence of large amounts of variation existing within nature. Natural selection is a far better means than traditional creation theory for explaining many of the anomalies found within nature independent of a creator. Although in later editions Darwin will add the words ‘the Creator’ on the concluding pages of Origin, it is quite clear that the theory of evolution through natural selection presented in this text is assumed to provide an alternate explanation to account for the magnificent creatures seen everywhere in the world. The many cases creation theory must admit as deleterious to its theory are quite contrarily explained and understood with ease through natural selection. By observing nature, its anomalies and similarities, its contradictions and imperfections, the mind must inherently appeal to natural selection.
The idea of evolution has been around since the times of the ancient Greeks; however, since Charles Darwin published his thesis The Origin of Species in 1859, many religious conservatives and scientists have been ambivalent in their support of his claims. Although Darwin’s rendition of ancient evolutionary philosophy mixed with his unadulterated fixation on pragmatism convinced many scientists of his time and the present of the accuracy of his claims, many people remain skeptical. Many objections from the religious field are based on the sociological, psychological, and philosophical implications of Darwin’s work and ideas which will not be discussed in this blog. Objections Darwin faces from the scientific field include: Darwin had no coherent mechanism through which hereditary traits are passed to offspring (he would later attempt and fail to explain inheritance as Pangenesis) and that there simply is not enough concrete evidence to support speciation via natural selection. However, several studies in the scientific field, including the Modern Synthesis or Dawin's evolutionary theory with Mendel's theory of genetic inheritance, provide evidence for many of Darwin’s claims and reveal that Darwin, although sometimes shooting in the dark, hit fairly close to home in many of his statements.
Darwin proposes a mechanism for speciation he terms natural selection. He argues in Origin of Species that organisms are strongly interconnected to their biotic and abiotic environments in extremely complex ways. Because of this, a change in one factor will inherently result in adaptation of organisms to cope with their new environments. He concludes that this affinity for phenotypic change in certain organisms may make them more fit than their counterparts and thus more likely to reproduce and pass on their genes to future offspring.
“Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring…I have called this by which each slight variation, if useful, is preserved, by the term natural selection.” (Darwin 1859 p 60).
Given this hypothesis, one would expect to see different adaptations for organisms living under different environmental conditions as is seen in studies on snails and Amazonian tribes. Snail shell shape and size on the same shore differ very significantly within a distance of only a few meters due to natural selection. Snails living on the upper shore have larger ridged and banded shells while the ones on the lower shore have smaller smooth and unbanded shells. The smaller shells of the snails living in high wave action areas are more flat and thin with wider apertures to accommodate a larger foot for combating the impact of the waves while the larger shells of the low wave action areas work as a mechanism for warding off predators such as craps (Conde-Padı´n et al. 2007). An investigation of six isolated tribes in the Amazon show possible evidence for selection against homozygous base pairing for a specific allele. Analysis of this specific allele shows strong favor for the probable selection of heterozygous base pairing which leads to the expression of a gene that defends against infection in high pathogen areas. “[although there may be some other factors involved], it seems improbable that the [specific homozygous] allele would be lost solely by chance in villages of six different tribes” (Mendes-Junior et al. 2007).
Darwin goes on to argue that the survivability of an organism designates its ability to propagate its genes. Since survivability depends extensively on the ability to obtain sustenance, and since food exists in limited quantities in the environment, a key factor in delegating which organisms will survive is whether or not it can obtain nourishment better than its competitors. He argues that without competition and with unlimited resources, species would propagate indefinitely, and it is the struggle for existence that keeps the order of nature.
“What checks the natural tendency of species to increase in numbers is most obscure. Look at the most vigorous species; by as much as it swarms in numbers, by so much will its tendency to increase be still further increased./ The amount of food for each species of course gives the extreme limit to which it can increase; but frequently it is not the obtaining of food, but the serving as prey to other animals, which determines the average number of a species” (Darwin 1859 p 64-65).
Eliminating leaf mining parasites (dipteran, a fly, and coleopteran, a beetle), from a tropical environment of leaf-mining insects, after only a year, significantly lowered levels of predation observed while significantly influencing abundance of foraging leaf mining insect populations due to increased food supply and decreased mortality rates (Morris et al. 2004). Speciation through natural selection due to competition has been supported by Jones and Ellner in their article on evolution and prey cycles, “A system of more than two prey types invariably collapses to one or two types in the presence of a predator: either a single clone that outcompetes all others, or a pair of very different clones, one very well defended and the other highly competitive, that together drive all intermediate prey types to extinction” (Jones and Ellner 2004, 2007, Yoshida et al. 2003). Yoshida et al. show that predator-prey competition can very quickly result in natural selection favoring enhanced prey survival in asexual organisms by observing the interactions between Brachionus calyciflorus (predator, planktonic rotifer) and Chlorella vulgaris (prey, green algae). When the green algae were placed in an environment occupied by abundant amounts of rotifers, the green algae population quickly diminished; however, it was not eliminated entirely. The surviving green algae were all small in size and thus provided little nutrients for the rotifers. The smaller size of these species made them more biologically ‘fit’ for their environment because they were contingent upon fewer nutrients and supplied too little sustenance for their predator population to survive. As the predator population began to die off, the prey multiplied more frequently and again grew larger to accommodate for the lack or predation. The hypothesis is that if this cycle were allowed to continue, the predators would accommodate for the influx in prey populations via selective forces (Yoshida et al. 2003).
One of the most trying issues of Darwin’s thesis was his emphasis on the importance of inheritance with no mechanism through which inheritance worked. He concluded that traits must be inherited because breeders have used artificial selection for centuries to make specialized individuals such as horned cattle and race horses.
“Any variation which is not inheritable is not important to us./ No breeder doubts how strong is the tendency of inheritance: like produces like is his fundamental belief…” (Darwin 1859 p 21).
The works of Mendel and the human genome project have laid out much of the groundwork to provide evidence for Darwin’s assumptions regarding the inheritability of traits. All organisms are made of cells, within these cells there is DNA which essentially designates how a cell will work. This DNA is made up of chromosomes with specific loci which contain many genes that are coded for by alleles (Human Genome Project 2015). In the case of most mammals, when the sex cells of parent organisms meet, they are each only haploid, and then combine to form a diploid cell called a zygote that has inherited roughly half its genes from each parent. Since each parent may have a specific trait as a result of their genotype (genetic make-up), this trait may be heritable and passed on to the offspring (Sá 2007). Since many of the occurrences during zygote formation are relatively random, this will not always be the case, thus modern biologists often create heritability characteristics for specific genes or phenotypes. Liddle’s Syndrome, an inheritable genetic disorder, causes hypertension due to excess function of a sodium channel. This disorder has been traced down to a single mutation on a gene that is passed from parent to offspring, “mutations were either stop codons or frame shifts that resulted in truncation of the carboxyl terminus of the b or g subunit of ENaC, indicating that the carboxyl terminal regions of the b and g subunits are essential for the function of ENaC” (Uehara et al. 1998). This highly specific claim, pinpointing the exact location, reason, and explanation of a genetically inheritable trait shows that although Darwin had no mechanism for inheritance, he definitely had the correct mindset.
When Darwin first published Origin of Species, it may have been highly controversial since many skeptics claimed it to be unscientific due lack of empirical evidence; however, much of the research in modern science work in favor of many of Darwin’s claims. Had Darwin understood a mechanism through which inheritability took place when publishing Origin, perhaps the general population would have been more accepting of his concepts and ideas. Given that more than 150 years have passed since the publication of the first edition, and with the massive expansion the scientific field has undergone, the evidence is still confirming his work; refutation of natural selection seems a near impossibility. Although modern society now has a better understanding of evolution and understands more completely the complex ways in which it can occur in the absence of natural selection (genetic drift for example), Origin of Species must be attributed for laying much of the groundwork for scientific studies that would follow. Given that genes are inheritable and that natural selection is observed in nature, the scientific community must accept that in some way or another, Darwin is right.
“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real” (Darwin 1859).
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8/12/2022 12:51:08 pm
Charles Darwin was a British naturalist who planned the theory of biological evolution by natural selection. He explained evolution as "descent with modification," the concept that species modifies over time, give hit to new species, and share and usual ancestor. The system that Darwin planned for evolution is natural selection. Because resources are restricted in nature, living things with genetic traits that suit the existence and reproduction that will appear to leave more brood than their peers, causing the attributes to increase in commonness over generations. Natural selection causes populations to become transformed, or additionally well-suited, to their environments over time. Natural selection relies on the environment and needs existing genetic variation in a group. Leave a Reply. |
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