Free evolution is the concept that natural processes can lead to the development of organisms over time. This includes the emergence and development of new species.
Numerous examples have been offered of this, including different varieties of fish called sticklebacks that can live in salt or fresh water, as well as walking stick insect varieties that favor particular host plants. These reversible traits, however, cannot explain fundamental changes in body plans.
Evolution by Natural Selection
The evolution of the myriad living organisms on Earth is an enigma that has intrigued scientists for many centuries. Charles Darwin's natural selection theory is the best-established explanation. This process occurs when those who are better adapted are able to reproduce faster and longer than those who are less well-adapted. Over time, a population of well-adapted individuals expands and eventually becomes a new species.
Natural selection is a cyclical process that is characterized by the interaction of three factors including inheritance, variation, and reproduction. Variation is caused by mutation and sexual reproduction both of which increase the genetic diversity within a species. Inheritance is the passing of a person's genetic characteristics to the offspring of that person which includes both dominant and recessive alleles. Reproduction is the process of producing fertile, viable offspring, which includes both asexual and sexual methods.
All of these factors must be in balance to allow natural selection to take place. If, for instance the dominant gene allele allows an organism to reproduce and live longer than the recessive allele then the dominant allele is more prevalent in a population. However, if the gene confers an unfavorable survival advantage or decreases fertility, it will disappear from the population. The process is self-reinforcing which means that the organism with an adaptive trait will survive and reproduce much more than those with a maladaptive trait. The more offspring an organism produces the more fit it is which is measured by its capacity to reproduce itself and live. People with desirable traits, like having a long neck in Giraffes, or the bright white color patterns on male peacocks, are more likely than others to survive and reproduce which eventually leads to them becoming the majority.
Natural selection is an aspect of populations and not on individuals. This is a significant distinction from the Lamarckian theory of evolution, which states that animals acquire traits through use or disuse. For instance, if a giraffe's neck gets longer through stretching to reach prey its offspring will inherit a more long neck. The differences in neck length between generations will continue until the giraffe's neck becomes so long that it can not breed with other giraffes.
Evolution by Genetic Drift
Genetic drift occurs when alleles of the same gene are randomly distributed in a group. At some point, only one of them will be fixed (become common enough that it can no more be eliminated through natural selection), and the rest of the alleles will drop in frequency. This can result in a dominant allele at the extreme. The other alleles are eliminated, and heterozygosity decreases to zero. In a small population, this could result in the complete elimination the recessive gene. 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 population.
A phenotypic 'bottleneck' can also occur when the survivors of a disaster like an outbreak or 에볼루션 a mass hunting event are confined to a small area. The survivors will be mostly homozygous for the dominant allele, which means that they will all share the same phenotype and therefore have the same fitness traits. This situation could be caused by earthquakes, war, or even plagues. Whatever the reason the genetically distinct group that remains could be susceptible to genetic drift.
Walsh Lewens and Ariew use Lewens, Walsh, and Ariew use a "purely outcome-oriented" definition of drift as any departure from the expected values of different fitness levels. They cite the famous example of twins who are both genetically identical and have exactly the same phenotype. However, one is struck by lightning and dies, while the other is able to reproduce.
This type of drift is crucial in the evolution of the species. However, it's not the only way to progress. The main alternative is a process called natural selection, in which the phenotypic diversity of an individual is maintained through mutation and migration.
Stephens claims that there is a vast difference between treating the phenomenon of drift as an agent or cause and treating other causes like migration and selection mutation as forces and causes. He argues that a causal mechanism account of drift allows us to distinguish it from these other forces, and this distinction is vital. He further argues that drift has an orientation, i.e., it tends towards eliminating heterozygosity. It also has a size, which is determined by population size.
Evolution by Lamarckism
Students of biology in high school are often introduced to Jean-Baptiste Lemarck's (1744-1829) work. His theory of evolution, also referred to as "Lamarckism which means that simple organisms develop into more complex organisms through inheriting characteristics that result from the organism's use and misuse. Lamarckism can be illustrated by an giraffe's neck stretching to reach higher leaves in the trees. This would cause the necks of giraffes that are longer to be passed on to their offspring who would then grow even taller.
Lamarck, a French Zoologist from France, presented an innovative idea in his opening lecture at the Museum of Natural History of Paris. He challenged the traditional thinking about organic transformation. According to him, living things had evolved from inanimate matter via a series of gradual steps. Lamarck was not the first to suggest that this could be the case, but the general consensus is that he was the one being the one who gave the subject its first broad and comprehensive analysis.
The prevailing story is that Lamarckism grew into a rival to Charles Darwin's theory of evolution by natural selection and both theories battled it out in the 19th century. Darwinism eventually prevailed, leading to what biologists call the Modern Synthesis. This theory denies acquired characteristics can be passed down and instead argues organisms evolve by the selective influence of environmental factors, such as Natural Selection.
Lamarck and his contemporaries believed in the idea that acquired characters could be passed on to the next generation. However, this idea was never a key element of any of their theories on evolution. This is partly because it was never tested scientifically.
It's been more than 200 years since Lamarck was born and in the age genomics there is a huge amount of evidence to support the heritability of acquired traits. This is also referred to as "neo Lamarckism", or more often epigenetic inheritance. It is a form of evolution that is as valid as the more well-known Neo-Darwinian theory.
Evolution by Adaptation
One of the most popular misconceptions about evolution is its being driven by a struggle to survive. In reality, this notion is a misrepresentation of natural selection and ignores the other forces that are driving evolution. The fight for survival can be more accurately described as a struggle to survive in a specific environment, which could be a struggle that involves not only other organisms but as well the physical environment.
To understand how evolution operates, it is helpful to consider what adaptation is. It refers to a specific feature that allows an organism to live and reproduce within its environment. It can be a physical feature, such as feathers or fur. Or it can be a behavior trait that allows you to move towards shade during hot weather or escaping the cold at night.
The ability of an organism to extract energy from its environment and interact with other organisms and their physical environment, is crucial to its survival. The organism must possess the right genes to produce offspring, and it should be able to locate enough food and other resources. Moreover, the organism must be capable of reproducing at an optimal rate within its environment.
These factors, together with gene flow and mutations can cause changes in the proportion of different alleles in the population's gene pool. The change in frequency of alleles could lead to the development of new traits, and eventually, new species in the course of time.
A lot of the traits we admire in animals and plants are adaptations, like lungs or gills to extract oxygen from the air, feathers or fur to protect themselves, long legs for running away from predators, and camouflage to hide. However, a proper understanding of adaptation requires attention to the distinction between behavioral and physiological characteristics.
Physiological adaptations, such as thick fur or gills, are physical traits, while behavioral adaptations, such as the desire to find companions or to retreat into the shade in hot weather, aren't. Furthermore, it is important to understand that a lack of forethought does not make something an adaptation. In fact, failure to think about the implications of a choice can render it unadaptable even though it might appear reasonable or even essential.
