The "Vicar of Bray" hypothesis (or Fisher-Muller Model [1] ) attempts to explain why sexual reproduction might have advantages over asexual reproduction. Reproduction is the process by which organisms give rise to offspring. Asexual reproduction [2] involves a single parent and results in offspring that are genetically identical to each other and to the parent.
In contrast to asexual reproduction, sexual reproduction involves two parents. Both the parents produce gametes through meiosis, a special type of cell division that reduces the chromosome number by half. [3] During an early stage of meiosis, before the chromosomes are separated in the two daughter cells, the chromosomes undergo genetic recombination. This allows them to exchange some of their genetic information. [4] Therefore, the gametes from a single organism are all genetically different from each other. The process in which the two gametes from the two parents unite is called fertilization. Half of the genetic information from both parents is combined. This results in offspring that are genetically different from each other and from the parents.
In short, sexual reproduction allows a continuous rearrangement of genes. Therefore, the offspring of a population of sexually reproducing individuals will show a more varied selection of phenotypes. Due to faster attainment of favorable genetic combinations, sexually reproducing populations evolve more rapidly in response to environmental changes. Under the Vicar of Bray hypothesis, sex benefits a population as a whole, but not individuals within it, making it a case of group selection. [5] [6]
Sexual reproduction often takes a lot of effort. Finding a mate can sometimes be an expensive, risky and time consuming process. Courtship, copulation and taking care of the new born offspring may also take up a lot of time and energy. From this point of view, asexual reproduction may seem a lot easier and more efficient. But another important thing to consider is that the individuals with the highest fitness are more likely to find a mate and reproduce. Therefore, the chances of offspring with a higher fitness increases. The Vicar of Bray hypothesis proposes that sexual reproduction is more beneficial than asexual reproduction, despite the cost of time and effort.
The hypothesis is called after the Vicar of Bray, a semi-fictionalized cleric who retained his ecclesiastic office by quickly adapting to the prevailing religious winds in England, switching between various Protestant and Catholic rites as the ruling hierarchy changed. [7] The figure described was Simon Aleyn between 1540 and 1588. The main work of Thomas Fuller (d. 1661), Worthies of England, describes this man: [8]
The vivacious vicar [of Bray] living under King Henry VIII, King Edward VI, Queen Mary, and Queen Elizabeth, was first a Papist, then a Protestant, then a Papist, then a Protestant again. He had seen some martyrs burnt (two miles off) at Windsor and found this fire too hot for his tender temper. This vicar, being taxed [attacked] by one for being a turncoat and an inconstant changeling, said, "Not so, for I always kept my principle, which is this – to live and die the Vicar of Bray." [9] – Worthies of England, published 1662
The hypothesis was first expressed in 1889 by August Weismann [10] and later by Guenther (1906). [11] Afterwards, the hypothesis was formulated in terms of population genetics by Fisher (1930) [12] and Muller (1932) [13] and with greater mathematical formalism, by Muller (1958, 1964) [14] [15] and Crow and Kimura (1965). [16] The doubts about the validity of the Vicar of Bray hypothesis caused the upcoming of alternative hypotheses such as:
Mathematical models have been used in order to try to prove or disprove these hypotheses. However, for a mathematical model, assumptions must be made. Assumptions on the size of the population, the breeding process, the environment, natural enemies and so on. That is why there will always be populations for which the model does not apply. Some models are better in explaining the ‘average’ population, while others better explain the smaller populations or populations that live in a more extreme environment. A good way to decide which model is the best might be to compare the expected result from the model with data from natural observations. [17]
People who criticize the Vicar of Bray hypothesis (and all other hypotheses that propose sexual reproduction has an advantage over asexual reproduction) say that sexual reproduction might be beneficial in some situations, but not always, which is why both ways of reproduction still exist. If either sexual reproduction or asexual reproduction would be much more beneficial, evolution should result in one of the two ways of reproduction to disappear and the other one to persist.
The Vicar of Bray Hypothesis, also referred to as Fisher-Muller Model in honour of its developers (Fisher 1930, Muller 1932) [...].
The 'classic' hypothesis (alias Fisher-Muller hypothesis) that sexual reproduction is evolutionarily advantageous because it allows a continuous rearrangement of genes [...], which Bell called 'The Vicar of Bray' [Bell, 1982], was first expressed by Weismann [Weismann, 1889] [...]. Afterwards, it has been formulated in terms of population genetics by Fisher [Fisher, 1930] and Muller [Muller, 1932] [...].
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Komodo dragons and some monitor lizards can reproduce asexually.
Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual.
In evolutionary genetics, Muller's ratchet is a process which, in the absence of recombination, results in an accumulation of irreversible deleterious mutations. This happens because in the absence of recombination, and assuming reverse mutations are rare, offspring bear at least as much mutational load as their parents. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination and consequent elimination of deleterious mutations. The negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms that do not undergo recombination.
In evolutionary genetics, mutational meltdown is a sub class of extinction vortex in which the environment and genetic predisposition mutually reinforce each other. Mutational meltdown is the accumulation of harmful mutations in a small population, which leads to loss of fitness and decline of the population size, which may lead to further accumulation of deleterious mutations due to fixation by genetic drift.
Evolution of sexual reproduction describes how sexually reproducing animals, plants, fungi and protists could have evolved from a common ancestor that was a single-celled eukaryotic species. Sexual reproduction is widespread in eukaryotes, though a few eukaryotic species have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals routinely reproduce asexually without entirely having lost sex. The evolution of sexual reproduction contains two related yet distinct themes: its origin and its maintenance. Bacteria and Archaea (prokaryotes) have processes that can transfer DNA from one cell to another, but it is unclear if these processes are evolutionarily related to sexual reproduction in Eukaryotes. In eukaryotes, true sexual reproduction by meiosis and cell fusion is thought to have arisen in the last eukaryotic common ancestor, possibly via several processes of varying success, and then to have persisted.
Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average individual taken from a population with a low genetic load will generally, when grown in the same conditions, have more surviving offspring than the average individual from a population with a high genetic load. Genetic load can also be seen as reduced fitness at the population level compared to what the population would have if all individuals had the reference high-fitness genotype. High genetic load may put a population in danger of extinction.
Human behavioral ecology (HBE) or human evolutionary ecology applies the principles of evolutionary theory and optimization to the study of human behavioral and cultural diversity. HBE examines the adaptive design of traits, behaviors, and life histories of humans in an ecological context. One aim of modern human behavioral ecology is to determine how ecological and social factors influence and shape behavioral flexibility within and between human populations. Among other things, HBE attempts to explain variation in human behavior as adaptive solutions to the competing life-history demands of growth, development, reproduction, parental care, and mate acquisition. HBE overlaps with evolutionary psychology, human or cultural ecology, and decision theory. It is most prominent in disciplines such as anthropology and psychology where human evolution is considered relevant for a holistic understanding of human behavior.
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.
The Red Queen's hypothesis is a hypothesis in evolutionary biology proposed in 1973, that species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species. The hypothesis was intended to explain the constant (age-independent) extinction probability as observed in the paleontological record caused by co-evolution between competing species; however, it has also been suggested that the Red Queen hypothesis explains the advantage of sexual reproduction at the level of individuals, and the positive correlation between speciation and extinction rates in most higher taxa.
Clonal interference is a phenomenon in evolutionary biology, related to the population genetics of organisms with significant linkage disequilibrium, especially asexually reproducing organisms. The idea of clonal interference was introduced by American geneticist Hermann Joseph Muller in 1932. It explains why beneficial mutations can take a long time to get fixated or even disappear in asexually reproducing populations. As the name suggests, clonal interference occurs in an asexual lineage ("clone") with a beneficial mutation. This mutation would be likely to get fixed if it occurred alone, but it may fail to be fixed, or even be lost, if another beneficial-mutation lineage arises in the same population; the multiple clones interfere with each other.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
The theoretical foundations of evolutionary psychology are the general and specific scientific theories that explain the ultimate origins of psychological traits in terms of evolution. These theories originated with Charles Darwin's work, including his speculations about the evolutionary origins of social instincts in humans. Modern evolutionary psychology, however, is possible only because of advances in evolutionary theory in the 20th century.
In biology, Gonozooids are any of the reproductive individuals of Tunicates, Bryozoan, or Hydrozoan colonies that produce gametes. Gonozooids may play a role in labour division or in alternation of generations. A gonozooid typically has hardly any other function than reproduction, amounting to little more than a motile gonad.
Social selection is a term used with varying meanings in biology.
Autogamy or self-fertilization refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species of protists have also been observed using autogamy as a means of reproduction. Flowering plants engage in autogamy regularly, while the protists that engage in autogamy only do so in stressful environments.
This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. Overlapping and related terms can be found in Glossary of cellular and molecular biology, Glossary of ecology, and Glossary of biology.
Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed "sperm parasitism" in reference to the somewhat pointless role of male gametes. Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually.
Germ-Soma Differentiation is the process by which organisms develop distinct germline and somatic cells. The development of cell differentiation has been one of the critical aspects of the evolution of multicellularity and sexual reproduction in organisms. Multicellularity has evolved upwards of 25 times, and due to this there is great possibility that multiple factors have shaped the differentiation of cells. There are three general types of cells: germ cells, somatic cells, and stem cells. Germ cells lead to the production of gametes, while somatic cells perform all other functions within the body. Within the broad category of somatic cells, there is further specialization as cells become specified to certain tissues and functions. In addition, stem cell are undifferentiated cells which can develop into a specialized cell and are the earliest type of cell in a cell lineage. Due to the differentiation in function, somatic cells are found only in multicellular organisms, as in unicellular ones the purposes of somatic and germ cells are consolidated in one cell.
Androgenesis occurs when a zygote is produced with only paternal nuclear genes. During standard sexual reproduction, one female and one male parent each produce haploid gametes, which recombine to create offspring with genetic material from both parents. However, in androgenesis, there is no recombination of maternal and paternal chromosomes, and only the paternal chromosomes are passed down to the offspring. The offspring produced in androgenesis will still have maternally inherited mitochondria, as is the case with most sexually reproducing species.