Intelligence has been defined in many ways, including: the capacity for logic, self-awareness, emotional knowledge, planning, critical thinking, problem solving. More it can be described as the ability to perceive or infer information, to retain it as knowledge to be applied towards adaptive behaviors within an environment or context. Intelligence is most studied in humans but has been observed in both non-human animals and in plants. Intelligence in machines is called artificial intelligence, implemented in computer systems using programs and, appropriate hardware; the word "intelligence" derives from the Latin nouns intelligentia or intellēctus, which in turn stem from the verb intelligere, to comprehend or perceive. In the Middle Ages, the word intellectus became the scholarly technical term for understanding, a translation for the Greek philosophical term nous; this term, was linked to the metaphysical and cosmological theories of teleological scholasticism, including theories of the immortality of the soul, the concept of the Active Intellect.
This entire approach to the study of nature was rejected by the early modern philosophers such as Francis Bacon, Thomas Hobbes, John Locke, David Hume, all of whom preferred the word "understanding" in their English philosophical works. Hobbes for example, in his Latin De Corpore, used "intellectus intelligit", translated in the English version as "the understanding understandeth", as a typical example of a logical absurdity; the term "intelligence" has therefore become less common in English language philosophy, but it has been taken up in more contemporary psychology. The definition of intelligence is controversial; some groups of psychologists have suggested the following definitions: From "Mainstream Science on Intelligence", an op-ed statement in the Wall Street Journal signed by fifty-two researchers: A general mental capability that, among other things, involves the ability to reason, solve problems, think abstractly, comprehend complex ideas and learn from experience. It is not book learning, a narrow academic skill, or test-taking smarts.
Rather, it reflects a broader and deeper capability for comprehending our surroundings—"catching on," "making sense" of things, or "figuring out" what to do. From Intelligence: Knowns and Unknowns, a report published by the Board of Scientific Affairs of the American Psychological Association: Individuals differ from one another in their ability to understand complex ideas, to adapt to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought. Although these individual differences can be substantial, they are never consistent: a given person's intellectual performance will vary on different occasions, in different domains, as judged by different criteria. Concepts of "intelligence" are attempts to organize this complex set of phenomena. Although considerable clarity has been achieved in some areas, no such conceptualization has yet answered all the important questions, none commands universal assent. Indeed, when two dozen prominent theorists were asked to define intelligence, they gave two dozen, somewhat different, definitions.
Besides those definitions and learning researchers have suggested definitions of intelligence such as: Human intelligence is the intellectual power of humans, marked by complex cognitive feats and high levels of motivation and self-awareness. Intelligence enables humans to remember descriptions of things and use those descriptions in future behaviors, it is a cognitive process. It gives humans the cognitive abilities to learn, form concepts and reason, including the capacities to recognize patterns, comprehend ideas, solve problems, use language to communicate. Intelligence enables humans to think. Note that much of the above definition applies to the intelligence of non-human animals. Although humans have been the primary focus of intelligence researchers, scientists have attempted to investigate animal intelligence, or more broadly, animal cognition; these researchers are interested in studying both mental ability in a particular species, comparing abilities between species. They study various measures of problem solving, as well as verbal reasoning abilities.
Some challenges in this area are defining intelligence so that it has the same meaning across species, operationalizing a measure that compares mental ability across different species and contexts. Wolfgang Köhler's research on the intelligence of apes is an example of research in this area. Stanley Coren's book, The Intelligence of Dogs is a notable book on the topic of dog intelligence. Non-human animals noted and studied for their intelligence include chimpanzees and other great apes, elephants and to some extent parrots and ravens. Cephalopod intelligence provides important comparative study. Cephalopods appear to exhibit characteristics of significant intelligence, yet their nervous systems differ radically from those of backboned animals. Vertebrates such as mammals, birds and fish have shown a high degree of intellect that varies according to each species; the same is true with arthropods. Evidence of a general factor of intell
A phenotypic trait trait, or character state is a distinct variant of a phenotypic characteristic of an organism. For example, eye color is a character of an organism, while blue and hazel are traits. A phenotypic trait is an obvious and measurable trait. An example of a phenotypic trait is hair color. Underlying genes, which make up the genotype, determine the hair color, but the hair color observed is the phenotype; the phenotype is dependent on the genetic make-up of the organism, influenced by the environmental conditions to which the organism is subjected across its ontogenetic development, including various epigenetic processes. Regardless of the degree of influence of genotype versus environment, the phenotype encompasses all of the characteristics of an organism, including traits at multiple levels of biological organization, ranging from behavior and evolutionary history of life traits, through morphology, cellular characteristics, components of biochemical pathways, messenger RNA; the inheritable unit that may influence a trait is called a gene.
A gene is a portion of a chromosome, a long and compacted string of DNA and proteins. An important reference point along a chromosome is the centromere; the nucleus of a diploid cell contains two of each chromosome, with homologous pairs of chromosomes having the same genes at the same loci. Different phenotypic traits are caused by different forms of genes, or alleles, which arise by mutation in a single individual and are passed on to successive generations. A gene is only a DNA code sequence. Alleles can be different and produce different product RNAs. Combinations of different alleles thus go on to generate different traits through the information flow charted above. For example, if the alleles on homologous chromosomes exhibit a "simple dominance" relationship, the trait of the "dominant" allele shows in the phenotype. Gregor Mendel pioneered modern genetics, his most famous analyses were based on clear-cut traits with simple dominance. He determined, his tool was statistics. The biochemistry of the intermediate proteins determines.
Therefore, biochemistry predicts. Extended expression patterns seen in diploid organisms include facets of incomplete dominance and multiple alleles. Incomplete dominance is the condition in which neither allele dominates the other in one heterozygote. Instead the phenotype is intermediate in heterozygotes, thus you can tell. Codominance refers to the allelic relationship that occurs when two alleles are both expressed in the heterozygote, both phenotypes are seen simultaneously. Multiple alleles refers to the situation when there are more than 2 common alleles of a particular gene. Blood groups in humans is a classic example; the ABO blood group proteins are important in determining blood type in humans, this is determined by different alleles of the one locus. Schizotypy is an example of a psychological phenotypic trait found in schizophrenia-spectrum disorders. Studies have shown that age influences the expression of schizotypal traits. For instance, certain schizotypal traits may develop further during adolescence, whereas others stay the same during this period.
Allometric engineering of traits Character displacement Phene Race Skill Lawrence, Eleanor Henderson's Dictionary of Biology. Pearson, Prentice Hall. ISBN 0-13-127384-1 Campbell, Neil.
A "polygene” or "multiple gene inheritance" is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait. The term "monozygous" is used to refer to a hypothetical gene as it is difficult to characterise the effect of an individual gene from the effects of other genes and the environment on a particular phenotype. Advances in statistical methodology and high throughput sequencing are, allowing researchers to locate candidate genes for the trait. In the case that such a gene is identified, it is referred to as a quantitative trait locus; these genes are pleiotropic as well. The genes that contribute to type 2 diabetes are thought to be polygenes. In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor of all organisms living on Earth. Traits with polygenic determinism correspond to the classical quantitative characters, as opposed to the qualitative characters with monogenic or oligogenic determinism. In essence instead of two options, such as freckles or no freckles, there are many variations.
Like the color of skin, hair, or eyes. Polygenic locus is any individual locus, included in the system of genes responsible for the genetic component of variation in a quantitative character. Allelic substitutions contribute to the variance in a specified quantitative character. Polygenic locus may be either a single or complex genetic locus in the conventional sense, i.e. either a single gene or linked block of functionally related genes. In modern sense, the inheritance mode of polygenic patterns is called polygenic inheritance, whose main properties may be summarized as follows: Most metric and meristic traits are controlled by a number of genetic loci. Main mode of nonallelic genes interaction in corresponding gene series is addition of small particular allele contributions; the effects of allelic substitution at each of the segregating genes are relatively small and interchangeable which results that identical phenotype may be displayed by a great variety of genotypes. The phenotypic expression of the polygenic characters is undergoing considerable modification by environmental influence.
Polygenic characters show a continuous rather than discontinuous distribution. Balanced systems of polygenic inheritance in a population contain a great deal of potential genetic variability in the heterozygous condition and released by small increments through genetic recombination between linked polygenes. Polygenic inheritance occurs; the genes are large in quantity but small in effect. Examples of human polygenic inheritance are skin color, eye color and weight. Polygenes exist in other organisms, as well. Drosophila, for instance, display polygeny with traits such as wing morphology, bristle count and many others; the frequency of the phenotypes of these traits follows a normal continuous variation distribution pattern. This results from the many possible allelic combinations; when the values are plotted, a bell-shaped curve is obtained. The mode of the distribution represents the optimal, or fittest, phenotype; the more genes are involved, the smoother the estimated curve. However, in this model all genes must code for alleles with additive effects.
This assumption is unrealistic as many genes display epistasis effects which can have unpredictable effects on the distribution of outcomes when looking at the distribution on a fine scale. Traditionally, mapping polygenes requires statistical tools available to help measure the effects of polygenes as well as narrow in on single genes. One of these tools is QTL-mapping. QTL-mapping utilizes a phenomenon known as linkage disequilibrium by comparing known marker genes with correlated phenotypes. Researchers will find a large region of DNA, called a locus, that accounts for a significant amount of the variation observed in the measured trait; this locus will contain a large number of genes that are responsible. A new form of QTL has been described as expression QTL. eQTLs regulate the amount of expressed mRNA, which in turn regulates the amount of protein within the organism. Another interest of statistical geneticists using QTL mapping is to determine the complexity of the genetic architecture underlying a phenotypic trait.
For example, they may be interested in knowing whether a phenotype is shaped by many independent loci, or by a few loci, do those loci interact. This can provide information on. Polygenic inheritance Quantitative trait locus Polygenie
In biology, a mutation is the permanent alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA or other genetic elements. Mutations result from errors during DNA replication or other types of damage to DNA, which may undergo error-prone repair, or cause an error during other forms of repair, or else may cause an error during replication. Mutations may result from insertion or deletion of segments of DNA due to mobile genetic elements. Mutations may or may not produce discernible changes in the observable characteristics of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution and the development of the immune system, including junctional diversity; the genomes of RNA viruses are based on RNA rather than DNA. The RNA viral genome can be double single stranded. In some of these viruses replication occurs and there are no mechanisms to check the genome for accuracy; this error-prone process results in mutations.
Mutation can result in many different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Mutations can occur in nongenic regions. One study on genetic variations between different species of Drosophila suggests that, if a mutation changes a protein produced by a gene, the result is to be harmful, with an estimated 70 percent of amino acid polymorphisms that have damaging effects, the remainder being either neutral or marginally beneficial. Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent or correct mutations by reverting the mutated sequence back to its original state. Mutations can involve the duplication of large sections of DNA through genetic recombination; these duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years.
Most genes belong to larger gene families of shared ancestry. Novel genes are produced by several methods through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions. Here, protein domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. For example, the human eye uses four genes to make structures that sense light: three for cone cell or color vision and one for rod cell or night vision. Another advantage of duplicating a gene is. Other types of mutation create new genes from noncoding DNA. Changes in chromosome number may involve larger mutations, where segments of the DNA within chromosomes break and rearrange. For example, in the Homininae, two chromosomes fused to produce human chromosome 2. In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less to interbreed, thereby preserving genetic differences between these populations.
Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, may have been important in the evolution of genomes. For example, more than a million copies of the Alu sequence are present in the human genome, these sequences have now been recruited to perform functions such as regulating gene expression. Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity. Nonlethal mutations increase the amount of genetic variation; the abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. For example, a butterfly may produce offspring with new mutations; the majority of these mutations will have no effect. If this color change is advantageous, the chances of this butterfly's surviving and producing its own offspring are a little better, over time the number of butterflies with this mutation may form a larger percentage of the population.
Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can increase in frequency over time due to genetic drift, it is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. DNA repair mechanisms are able to mend most changes before they become permanent mutations, many organisms have mechanisms for eliminating otherwise-permanently mutated somatic cells. Beneficial mutations can improve reproductive success. Mutationism is one of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book, On the Origin of Species. In the theory, mutation was the source of novelty
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA, or in chloroplasts as chloroplast DNA. In contrast, prokaryotes store their DNA only in circular chromosomes.
Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix. The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide.
A biopolymer comprising multiple linked nucleotides is called a polynucleotide. The backbone of the DNA strand is made from alternating sugar residues; the sugar in DNA is 2-deoxyribose, a pentose sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings; these are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. When imagining DNA, each phosphoryl is considered to "belong" to the nucleotide whose 5′ carbon forms a bond therewith. Any DNA strand therefore has one end at which there is a phosphoryl attached to the 5′ carbon of a ribose and another end a
Epigenetics is the study of heritable phenotype changes that do not involve alterations in the DNA sequence. The Greek prefix epi- in epigenetics implies features that are "on top of" or "in addition to" the traditional genetic basis for inheritance. Epigenetics most denotes changes that affect gene activity and expression, but can be used to describe any heritable phenotypic change; such effects on cellular and physiological phenotypic traits may result from external or environmental factors, or be part of normal development. The standard definition of epigenetics requires these alterations to be heritable, either in the progeny of cells or of organisms; the term refers to the changes themselves: functionally relevant changes to the genome that do not involve a change in the nucleotide sequence. Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence. Gene expression can be controlled through the action of repressor proteins that attach to silencer regions of the DNA.
These epigenetic changes may last through cell divisions for the duration of the cell's life, may last for multiple generations though they do not involve changes in the underlying DNA sequence of the organism. One example of an epigenetic change in eukaryotic biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become differentiated cells. In other words, as a single fertilized egg cell – the zygote – continues to divide, the resulting daughter cells change into all the different cell types in an organism, including neurons, muscle cells, endothelium of blood vessels, etc. by activating some genes while inhibiting the expression of others. Some phenomena not heritable have been described as epigenetic. For example, the term epigenetic has been used to describe any modification of chromosomal regions histone modifications, whether or not these changes are heritable or associated with a phenotype.
The consensus definition now requires a trait to be heritable. The term epigenetics in its contemporary usage emerged in the 1990s, but for some years has been used in somewhat variable meanings. A consensus definition of the concept of epigenetic trait as "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence" was formulated at a Cold Spring Harbor meeting in 2008, although alternate definitions that include non-heritable traits are still being used; the term epigenesis has a generic meaning "extra growth". It has been used in English since the 17th century. From the generic meaning, the associated adjective epigenetic, C. H. Waddington coined the term epigenetics in 1942 as pertaining to epigenesis, in parallel to Valentin Haecker's'phenogenetics'. Epigenesis in the context of the biology of that period referred to the differentiation of cells from their initial totipotent state in embryonic development; when Waddington coined the term, the physical nature of genes and their role in heredity was not known.
Waddington held that cell fates were established in development much as a marble rolls down to the point of lowest local elevation. Waddington suggested visualising increasing irreversibility of cell type differentiation as ridges rising between the valleys where the marbles are travelling. In recent times Waddington's notion of the epigenetic landscape has been rigorously formalized in the context of the systems dynamics state approach to the study of cell-fate. Cell-fate determination is predicted to exhibit certain dynamics, such as attractor-convergence or oscillatory; the term "epigenetic" has been used in developmental psychology to describe psychological development as the result of an ongoing, bi-directional interchange between heredity and the environment. Interactivist ideas of development have been discussed in various forms and under various names throughout the 19th and 20th centuries. An early version was proposed, among the founding statements in embryology, by Karl Ernst von Baer and popularized by Ernst Haeckel.
A radical epigenetic view was developed by Paul Wintrebert. Another variation, probabilistic epigenesis, was presented by Gilbert Gottlieb in 2003; this view encompasses all of the possible developing factors on an organism and how they not only influence the organism and each other, but how the organism influences its own development. The developmental psychologist Erik Erikson wrote of an epigenetic principle in his book Identity: Youth and Crisis, encompassing the notion that we develop through an unfolding of our personality in predetermined stages, that our environment and surrounding culture influence how we progress through these stages; this biological unfolding in relation to our socio-cultural settings is done in stages of psychosocial development, where "progress through each stage is in part determined by our success, or lack of success, in all the previous stages." Robin Holliday defined epigenetics as "the study of the mechanisms of temporal and spatial control of gene activity during the development of complex organisms."
Thus epigenetic can be used to describe anything other than DNA s
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits and disorders. Twin research is considered a key tool in behavioral genetics and in content fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, etc; these studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia. Twins are a valuable source for observation because they allow the study of environmental influence and varying genetic makeup: "identical" or monozygotic twins share 100% of their genes, which means that most differences between the twins are due to experiences that one twin has but not the other twin. "Fraternal" or dizygotic twins share only about 50 % of the same as any other sibling. Twins share many aspects of their environment because they are born into the same family.
The presence of a given genetic trait in only one member of a pair of identical twins provides a powerful window into environmental effects. Twins are useful in showing the importance of the unique environment when studying trait presentation. Changes in the unique environment can stem from an event or occurrence that has only affected one twin; this could range from a head injury or a birth defect that one twin has sustained while the other remains healthy. The classical twin design compares the similarity of dizygotic twins. If identical twins are more similar than fraternal twins, this implicates that genes play an important role in these traits. By comparing many hundreds of families with twins, researchers can understand more about the roles of genetic effects, shared environment, unique environment in shaping behavior. Modern twin studies have concluded that all traits are in part influenced by genetic differences, with some characteristics showing a stronger influence, others an intermediate level and some more complex heritabilities, with evidence for different genes affecting different aspects of the trait – as in the case of autism.
The methodological assumptions on which twin studies are based, have been criticized as untenable. Twins have been of interest to scholars since early civilization, including the early physician Hippocrates, who attributed different diseases in twins to different material circumstances, the stoic philosopher Posidonius, who attributed such similarities to shared astrological circumstances. More recent study is from Sir Francis Galton's pioneering use of twins to study the role of genes and environment on human development and behavior. Galton, was unaware of the difference between identical and DZ twins; this factor was still not understood when the first study using psychological tests was conducted by Edward Thorndike using fifty pairs of twins. This paper was an early statement of the hypothesis, his study compared twin pairs age 9–10 and 13–14 to normal siblings born within a few years of one another. Thorndike incorrectly reasoned that his data supported for there being one, not twin types.
This mistake was repeated by Ronald Fisher, who argued The preponderance of twins of like sex, does indeed become a new problem, because it has been believed to be due to the proportion of identical twins. So far as I am aware, however, no attempt has been made to show that twins are sufficiently alike to be regarded as identical exist in sufficient numbers to explain the proportion of twins of like sex. An early, first, study understanding the distinction is from the German geneticist Hermann Werner Siemens in 1924. Chief among Siemens' innovations was the polysymptomatic similarity diagnosis; this allowed him to account for the oversight that had stumped Fisher, was a staple in twin research prior to the advent of molecular markers. Wilhelm Weinberg and colleagues in 1910 used the identical-DZ distinction to calculate respective rates from the ratios of same- and opposite-sex twins in a maternity population, they partitioned co-variation amongst relatives into genetic and environmental elements, anticipating the work of Fisher and Wright, including the effect of dominance on similarity of relatives, beginning the first classic-twin studies.
A study conducted by Darrick Antell and Eva Taczanowski found that "twins showing the greatest discrepancies in visible aging signs had the greatest degree of discordance between personal lifestyle choices and habits", concluded that "the genetic influences on aging may be overrated, with lifestyle choices exerting far more important effects on physical aging." Examples of prominent twin studies include the following: Maudsley Bipolar Twin Study Minnesota Twin Family Study Twins Early Development Study The power of twin designs arises from the fact that twins may be either monozygotic – or dizygotic. These known differences in genetic similarity, together with a testable assumption of equal environment