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Free evolution is the notion that natural processes can cause organisms to evolve over time. This includes the appearance and development of new species.
This has been proven by many examples of stickleback fish species that can live in saltwater or fresh water and walking stick insect varieties that have a preference for particular host plants. These typically reversible traits are not able to explain fundamental changes to basic body plans.
Evolution through Natural Selection
Scientists have been fascinated by the development of all the living creatures that live on our planet for ages. The most widely accepted explanation is that of Charles Darwin's natural selection, an evolutionary process that occurs when individuals that are better adapted survive and reproduce more successfully than those who are less well adapted. Over time, the population of well-adapted individuals becomes larger and eventually develops into a new species.
Natural selection is a process that is cyclical and involves the interaction of 3 factors including reproduction, variation and inheritance. Sexual reproduction and mutation increase the genetic diversity of the species. Inheritance is the transfer of a person's genetic characteristics to their offspring which includes both recessive and dominant alleles. Reproduction is the process of generating fertile, viable offspring. This can be accomplished by both asexual or sexual methods.
All of these elements must be in harmony for natural selection to occur. If, for instance, a dominant gene allele allows an organism to reproduce and live longer than the recessive gene allele, then the dominant allele will become more common in a population. However, if the gene confers a disadvantage in survival or decreases fertility, it will be eliminated from the population. This process is self-reinforcing which means that an organism with an adaptive trait will live and reproduce more quickly than one with a maladaptive characteristic. The more offspring that an organism has the more fit it is, which is measured by its ability to reproduce and survive. Individuals with favorable traits, such as longer necks in giraffes, or bright white colors in male peacocks are more likely survive and have offspring, which means they will eventually make up the majority of the population over time.
Natural selection is only a factor in populations and not on individuals. This is a significant distinction from the Lamarckian evolution theory which holds that animals acquire traits either through use or lack of use. For example, if a giraffe's neck gets longer through reaching out to catch prey and its offspring will inherit a more long neck. The difference in neck size between generations will increase until the giraffe is unable to breed with other giraffes.
Evolution by Genetic Drift
In genetic drift, the alleles of a gene could attain different frequencies within a population due to random events. At some point, one will reach fixation (become so common that it is unable to be removed by natural selection) and other alleles will fall to lower frequencies. This could lead to a dominant allele in extreme. The other alleles have been virtually eliminated and heterozygosity been reduced to zero. In a small population, this could lead to the complete elimination of the recessive allele. This scenario is called the bottleneck effect. It is typical of an evolution process that occurs when a large number individuals migrate to form a group.
A phenotypic bottleneck may happen when the survivors of a catastrophe like an epidemic or a mass hunting event, are concentrated into a small area. The survivors will share an dominant allele, and will have the same phenotype. This situation could be caused by war, earthquakes or even plagues. Whatever the reason the genetically distinct group that is left might be susceptible to genetic drift.
Walsh Lewens, Lewens, and Ariew employ Lewens, Walsh and Ariew employ a "purely outcome-oriented" definition of drift as any deviation from the expected values for different fitness levels. They cite a famous instance of twins who are genetically identical, have identical phenotypes and yet one is struck by lightning and dies, while the other lives and reproduces.
This kind of drift can be very important in the evolution of an entire species. However, it's not the only way to develop. Natural selection is the main alternative, where mutations and migrations maintain the phenotypic diversity in the population.
Stephens asserts that there is a significant difference between treating drift as a force, or a cause and treating other causes of evolution such as selection, mutation, and migration as forces or causes. He argues that a causal process account of drift permits us to differentiate it from the other forces, and this distinction is crucial. He further argues that drift is both a direction, i.e., it tends to reduce heterozygosity. It also has a size which is determined based on the size of the population.
Evolution through Lamarckism
Students of biology in high school are often introduced to Jean-Baptiste Lamarck's (1744-1829) work. His theory of evolution is often called "Lamarckism" and it states that simple organisms grow into more complex organisms through the inheritance of characteristics that result from the natural activities of an organism usage, use and disuse. Lamarckism is illustrated through a giraffe extending its neck to reach higher branches in the trees. This would cause the longer necks of giraffes to be passed onto their offspring who would grow taller.
Lamarck was a French Zoologist. In his inaugural lecture for his course on invertebrate Zoology at the Museum of Natural History in Paris on the 17th of May in 1802, he introduced an original idea that fundamentally challenged the conventional wisdom about organic transformation. According to him living things had evolved from inanimate matter through the gradual progression of events. Lamarck was not the only one to suggest that this might be the case, but the general consensus is that he was the one being the one who gave the subject its first general and thorough treatment.
The most popular story is that Charles Darwin's theory of natural selection and Lamarckism fought during the 19th century. Darwinism ultimately prevailed and led to what biologists refer to as the Modern Synthesis. The theory denies that acquired characteristics can be passed down and instead argues that organisms evolve through the influence of environment factors, including Natural Selection.
Although Lamarck believed in the concept of inheritance by acquired characters and his contemporaries spoke of this idea, it was never an integral part of any of their evolutionary theories. This is due to the fact that it was never scientifically tested.
However, it has been more than 200 years since Lamarck was born and in the age genomics there is a vast amount of evidence to support the possibility of inheritance of acquired traits. This is sometimes referred to as "neo-Lamarckism" or, more frequently, epigenetic inheritance. It is a version of evolution that is as valid as the more well-known neo-Darwinian model.
Evolution by adaptation
One of the most widespread misconceptions about evolution is that it is driven by a type of struggle for survival. This view is inaccurate and overlooks the other forces that determine the rate of evolution. The fight for survival can be more effectively described as a struggle to survive within a specific environment, which may be a struggle that involves not only other organisms but as well the physical environment.
To understand how evolution works, it is helpful to think about what adaptation is. It refers to a specific feature that allows an organism to live and reproduce in its environment. It could be a physical feature, such as feathers or fur. It could also be a characteristic of behavior, like moving to the shade during hot weather or coming out to avoid the cold at night.
The ability of an organism to draw energy from its environment and interact with other organisms as well as their physical environments is essential to its survival. The organism must possess the right genes to create offspring, and be able to find sufficient food and resources. The organism should be able to reproduce itself at a rate that is optimal for its particular niche.
These elements, along with mutations and gene flow can cause changes in the proportion of different alleles within a population’s gene pool. As time passes, this shift in allele frequency can lead to the emergence of new traits and ultimately new species.
Many of the characteristics we find appealing in plants and animals are adaptations. For example lung or gills that extract oxygen from the air, fur and feathers as insulation and long legs to get away from predators and camouflage for hiding. To understand adaptation it is crucial to differentiate between physiological and behavioral traits.
Physiological adaptations, such as thick fur or gills are physical traits, while behavioral adaptations, such as the desire to find companions or to move to the shade during hot weather, aren't. In addition, it is important to note that a lack of forethought does not mean that something is an adaptation. Inability to think about the implications of a choice even if it seems to be logical, can make it inflexible.