Evolutionary Principles - Biology

Genetic drift can be defined as changes in allele frequencies in a population caused by random events or chance. Large populations are capable of retaining fairly stable allele frequencies, thereby maintaining a small degree of genetic drift.

In contrast, in a small population, either losing the alleles of a single individual or an over-contribution by a single individual in reproduction can significantly change the frequency of alleles within the population. This could eventually lead to the loss of alleles from the population.

The endosymbotic theory describes the evolution of eukaryotic cells from prokaryotes. Small independent organisms were engulfed by larger ones; both were prokaryotic and unicellular. This engulfment benefited both organisms, and the genes that promoted this engulfment were selected for. Over a long time, eukaryotic cells evolved with many membrane-bound organelles, each with their own specific structure.

Evolution must occur over many generations and a long time scale. Changes within the life of an individual do not constitute evolution. Thus, a tadpole becoming a frog is not evolution.

After the Industrial Revolution's smog polluted the trees and resulted in them darkening in color, it was much easier for the black moths to survive and reproduce, because the darkened trees provided them with better camouflage than the light-colored trees had. The white-colored moths, on the other hand, were now exposed to predation at a greater rate, because they were not camouflaged. Due to this change in the environment, the moth population became predominantly black-colored as it adapted. This is an example of natural selection in action.

The mechanism of evolution was described by Darwin as the "survival of the fittest." We need an answer that addresses the fact that the individuals best suited to survival pass on their genes more often than individuals that aren't as well-suited, and that over long periods of time, these changes an accumulate until new species arise. This means that the correct answer is "There are always differences in the genes of individuals of a species. Some differences give certain individuals a better chance of survival. In each generation, those individuals best-suited to survive the current conditions will have the highest success in passing on their genes. Over many generations, the accumulation of these changes leads to the creation of new species from existing species."

A selective pressure is a factor that promotes evolution by selecting for a trait that will allow better survival for the organism that is at risk for compromised survival. In the case of anoles, the presence of the brown anole has promoted an evolutionary change for the green anole. There is no evolutionary change that can be observed in the other instances.

Coevolution describes how two species that interact closely with each other for their survival can evolve in response to one another. Another example is lichens, which are fungi and bacterial cells that grow together to act as a single living organism.

Evolution occurs over a given time and may be punctuated or stagnant. As individuals are produced with different characteristics more fit for their environments, the population gradually changes. Evolution may even cause speciation or the merging of two species. Evolution is the response of a changing environment and different species interactions- individuals do not evolve; rather, natural selection works in favor of those individuals who are more fit for the current environment. Those more fit individuals will go on to produce more offspring with their same qualities, leading to a gradual change, or evolution, of a species, population, and community.

Sexual dimorphism is a phenotypic differentiation between males and females of the same species. These altered phenotypes occur in organisms that reproduce through sexual reproduction. Commonly referenced possible examples are body size, physical strength and morphology, ornamentation, behavior and other bodily traits. An example would be comparing bright green male peacocks to the brown and grey female peacocks. Genetic drift is a different, unrelated evolutionary concept. Evolutionary monomorphism and the sperm-egg model do not refer to real concepts.

The biological fitness of an organism is dependent on its ability to survive and reproduce in a given environment. If different traits or alleles increase the fitness of an organism, those alleles will consequently increase in the gene pool, and that trait will increase in the population. This is how natural selection affects a population.

There is inherent trade-off in biological fitness. A trait that increases ability to survive, but makes an individual sterile, decreases fitness because the organism cannot produce offspring to carry on the trait. Similarly, if a trait increases the ability to reproduce, but makes it harder to the organism to survive, it may die before being able to produce offspring. Both survival and reproduction are essential to defining the fitness of an organism.

Biological fitness in the evolutionary sense is only related to fitness in terms to reproduction. Because the primary goal of all organisms is to reproduce, or to pass their DNA onto offspring, fitness is defined as the ability to reproduce and create viable offspring.

"Favorable" traits, such as intelligence, size, or strength, may increase the ability of an individual to survive and reproduce, thus increasing biological fitness, but cannot be used to directly define the fitness of the individual.

All of the examples given provide an evolutionary advantage. A white rabbit in a snow covered environment has camouflage, which protects it from its predators. The same is true with the black moth living in a in a soot-covered industrial area. A cheeta that can run fastest has the greatest chance of catching prey and feeding himself/herself and his/her offspring. The same is true for a bird that can crack nuts in an area where nuts are the main source of food.

The term "fitness" in evolutionary biology means the ability of an organism to pass on its genetic material to its offspring. Biological or "Darwinian" fitness is being able to live long enough to reproduce and keep the population or species alive. Most students confuse biological fitness with physical fitness because that is the context most often associated with the word.

Biological or Darwinian fitness is defined based on the specimen's ability to reproduce and generate viable offspring. Essentially, the fitness of the individual is based on its ability to pass genetic information on to the next generation, as opposed to any physical characteristic or trait.

Measuring the number of offspring who contribute to the gene pool is the best way to determine how genetically fit the iguana is. No matter how strong, large, old, or free of predation an animal is, if it cannot reproduce, it is not considered fit.

The term biological fitness refers to reproductive success and is different than physical fitness. Since the most spotted male fathered the most cubs that survived to adulthood to reproduce themselves, he would be considered the most biologically fit. It is also important to note the inclusion of the "survived to adulthood" aspect since reproductive success is dependent on an organism's offspring being able to reproduce and contribute to the gene pool as well. For example, if the most spotted male had fathered a litter that initially had nine cubs, but only one of them survived to adulthood to have cubs of its own, he would no longer be considered the most biologically fit.

Parasitism is a relationship in which one organism benefits at the expense of the other organism. Parasites often take nutrients from their hosts, causing malnutrition, poor immunity, and death. For example, tapeworms can consume food digested by an organism before it can be absorbed by the intestine, leading to poor nutrition and death.

Commensalism is a relationship between two organisms in which one organism benefits without affecting the other. Commensalists often gain protection from their hosts, remaining self-sufficient without relying on the host for energy. For example, barnacles can live on the bellies of whales and feed on the plankton in the surrounding water, while gaining transportation and protection from the whale. The whale is not affected.

Mutualism is a relationship between two organisms in which both organisms benefit. Mutualistic organisms frequently help to prevent disease in their hosts. For example, bacteria in the gut help to digest foreign materials and other bacteria, preventing disease in humans while receiving nutrients.

Competition is an interaction between species during which two species receive limited resources and must compete with one another for survival. Evolution is the gradual change in the traits of a species.

Development of genetically modified organisms is an example of artificial selection due to human intervention. Desirable organisms are allowed to generate offspring, passing on the selected genes. Non-optimal organisms are prevented from creating offspring.

The other options are all evolutionary changes that occurred naturally. Snake coloration is a mechanism to avoid predators and stalk prey. A giraffe's neck facilitates accessibility to its food source. An insect that is resistant to a certain chemical will survive to create offspring.

As an example of decent with modification, Darwin observed different species of finches on the Galapagos Islands and thought that they had descended from a common ancestor. Individuals that have inherited advantageous traits are likely to produce more offspring than other members of the population, which drives natural selection. This occurs within a particular environment or geographic location. Decent with modification is essentially the theory of inherited mutations that can alter the gene pool of a population, eventually resulting in speciation.

Natural selection is the unequal survival and reproduction of organisms resulting in the preservation of favorable adaptations. Natural selection favors individuals with higher biological fitness, which is defined by the individual's ability to produce viable offspring.

Convergent evolution is the independent evolution of similar structures among unrealted organisms as a result of similar environmental pressures. Evolution is any change in the proportions of different genotypes in a population from one generation to the next. Genetic drift is a change in the allele frequencies of a small population purely by chance. An adaptation is a characteristic of an organism that helps it survive and reproduce in a particular environment.