What is Free Evolution?
Free evolution is the notion that the natural processes that organisms go through can cause them to develop over time. This includes the appearance and development of new species.
This is evident in many examples such as the stickleback fish species that can live in fresh or saltwater and walking stick insect types that have a preference for particular host plants. These reversible traits are not able to explain fundamental changes to the basic body plan.
Evolution by Natural Selection
The evolution of the myriad living creatures on Earth is an enigma that has intrigued scientists for many centuries. The best-established explanation is Charles Darwin's natural selection process, which is triggered when more well-adapted individuals live longer and reproduce more successfully than those that are less well adapted. As time passes, the number of individuals who are well-adapted grows and eventually creates an entirely new species.
Natural selection is an ongoing 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 term used to describe the transmission of a person's genetic characteristics, which includes recessive and dominant genes and their offspring. Reproduction is the process of producing viable, fertile offspring. This can be accomplished via sexual or asexual methods.
Natural selection only occurs when all these elements are in equilibrium. If, for instance, a dominant gene allele makes an organism reproduce and live longer than the recessive allele, then the dominant allele will become more prevalent in a group. But if the allele confers a disadvantage in survival or reduces fertility, it will disappear from the population. This process is self-reinforcing which means that an organism with an adaptive trait will survive and reproduce more quickly than those with a maladaptive trait. The higher the level of fitness an organism has, measured by its ability reproduce and survive, is the more offspring it can produce. People with desirable traits, like having a longer neck 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 in the future.
Natural selection is only a force for populations, not individual organisms. This is a major distinction from the Lamarckian theory of evolution which claims that animals acquire characteristics through use or disuse. For instance, if the giraffe's neck gets longer through stretching to reach prey, its offspring will inherit a more long neck. The difference in neck length between generations will continue until the giraffe's neck becomes so long that it can no longer breed with other giraffes.
Evolution by Genetic Drift
Genetic drift occurs when the alleles of one gene are distributed randomly in a group. At some point, one will attain fixation (become so common that it is unable to be removed by natural selection) and other alleles will fall to lower frequencies. This can lead to a dominant allele in extreme. The other alleles are virtually eliminated and heterozygosity decreased to a minimum. In a small population this could lead to the complete elimination the recessive gene. This is known as the bottleneck effect. It is typical of an evolutionary process that occurs whenever an enormous number of individuals move to form a population.
A phenotypic bottleneck can also occur when the survivors of a catastrophe like an epidemic or mass hunting event, are concentrated within a narrow area. The remaining individuals will be mostly homozygous for the dominant allele, meaning that they all share the same phenotype and will therefore share the same fitness characteristics. This can be caused by earthquakes, war, or even plagues. Regardless of the cause the genetically distinct population that remains is susceptible to genetic drift.
Walsh Lewens, Walsh and Ariew define drift as a departure from the expected values due to differences in fitness. They provide the famous case of twins who are genetically identical and have exactly the same phenotype. However, one is struck by lightning and dies, whereas the other is able to reproduce.
This type of drift can play a crucial part in the evolution of an organism. However, it's not the only method to develop. Natural selection is the most common alternative, in which mutations and migrations maintain the phenotypic diversity of the population.
Stephens argues that there is a major difference between treating drift as a force, or a cause and considering other causes of evolution like mutation, selection and migration as causes or causes. He argues that a causal-process model of drift allows us to separate it from other forces and that this differentiation is crucial. He also claims that drift has a direction, that is, it tends to eliminate heterozygosity, and that it also has a magnitude, that is determined by the size of the population.
Evolution by Lamarckism
Biology students in high school are often introduced to Jean-Baptiste Lemarck's (1744-1829) work. His theory of evolution is commonly known as "Lamarckism" and it states that simple organisms develop into more complex organisms through the inheritance of characteristics which result from the natural activities of an organism usage, use and disuse. Lamarckism can be illustrated by the giraffe's neck being extended to reach higher branches in the trees. This could cause giraffes' longer necks to be passed onto their offspring who would then grow even taller.
Lamarck, a French Zoologist from France, presented an idea that was revolutionary in his opening lecture at the Museum of Natural History of Paris. He challenged the conventional wisdom on organic transformation. In his view, living things had evolved from inanimate matter via a series of gradual steps. Lamarck wasn't the first to propose this but he was regarded as the first to provide the subject a comprehensive and general explanation.
The dominant story is that Charles Darwin's theory of natural selection and Lamarckism were competing in the 19th Century. Darwinism eventually won and led to the creation of what biologists today refer to as the Modern Synthesis. The theory argues that traits acquired through evolution can be inherited and instead argues that organisms evolve by the symbiosis of environmental factors, such as natural selection.
Although Lamarck supported the notion of inheritance through acquired characters and his contemporaries paid lip-service to this notion however, it was not a central element in any of their evolutionary theories. This is due to the fact that it was never scientifically tested.
But it is now more than 200 years since Lamarck was born and in the age of genomics, there is a large amount of evidence to support the possibility of inheritance of acquired traits. This is referred to as "neo Lamarckism", or more commonly epigenetic inheritance. It is a variant of evolution that is just as relevant as the more popular neo-Darwinian model.
Evolution by adaptation
One of the most common misconceptions about evolution is that it is being driven by a struggle to survive. This view is inaccurate and overlooks other forces that drive evolution. The fight for survival can be better described as a fight to survive in a certain environment. This can include not just other organisms as well as the physical environment.
To understand how evolution operates, it is helpful to understand what is adaptation. The term "adaptation" refers to any characteristic that allows a living thing to live in its environment and reproduce. It can be a physical feature, such as feathers or fur. It could also be a trait of behavior, like moving to the shade during hot weather, or coming out to avoid the cold at night.
The survival of an organism is dependent on its ability to extract energy from the surrounding environment and interact with other organisms and their physical environments. The organism must possess the right genes to generate offspring, and it must be able to find sufficient food and other resources. The organism should also be able reproduce at an amount that is appropriate for its particular niche.
These factors, in conjunction with mutations and gene flow, can lead to a shift in the proportion of different alleles within a population’s gene pool. Over time, this change in allele frequencies can result in the emergence of new traits, and eventually new species.
Many of the characteristics we admire in plants and animals are adaptations. For instance, lungs or gills that draw oxygen from air feathers and fur as insulation long legs to run away from predators, and camouflage to hide. To understand the concept of adaptation it is essential to differentiate between physiological and behavioral traits.
Physiological adaptations, such as thick fur or gills, are physical traits, while behavioral adaptations, like the tendency to seek out companions or to move to the shade during hot weather, aren't. It is also important to keep in mind that the absence of planning doesn't make an adaptation. Failure to consider the implications of a choice even if it appears to be rational, could make it unadaptive.