When the sperm fertilises the egg, two copies of each chromosome are present and therefore two copies of each gene , and so an embryo forms. The chromosomes that determine the sex of the baby X and Y chromosomes are called sex chromosomes. A person with an XX pairing of sex chromosomes is biologically female, while a person with an XY pairing is biologically male.
As well as determining sex, the sex chromosomes carry genes that control other body functions. There are many genes located on the X chromosome, but only a few on the Y chromosome. Genes that are on the X chromosome are said to be X-linked. Genes that are on the Y chromosome are said to be Y-linked.
Parents pass on traits or characteristics, such as eye colour and blood type, to their children through their genes. Some health conditions and diseases can be passed on genetically too. Sometimes, one characteristic has many different forms.
Changes or variations in the gene for that characteristic cause these different forms. These two copies of the gene contained in your chromosomes influence the way your cells work. The two alleles in a gene pair are inherited, one from each parent.
Alleles interact with each other in different ways. These are called inheritance patterns. Examples of inheritance patterns include:. An allele of a gene is said to be dominant when it effectively overrules the other recessive allele. The allele for brown eyes B is dominant over the allele for blue eyes b. So, if you have one allele for brown eyes and one allele for blue eyes Bb , your eyes will be brown.
This is also the case if you have two alleles for brown eyes, BB. However, if both alleles are for the recessive trait in this case, blue eyes, bb you will inherit blue eyes. For blood groups, the alleles are A, B and O. The A allele is dominant over the O allele. Blood group A is said to have a dominant inheritance pattern over blood group O.
If the father has two O alleles OO , he has the blood group O. For each child that couple has, each parent will pass on one or the other of those two alleles. This is shown in figure 1. This means that each one of their children has a 50 per cent chance of having blood group A AO and a 50 per cent chance of having blood group O OO , depending on which alleles they inherit. The combination of alleles that you have is called your genotype e. The observable trait that you have — in this case blood group A — is your phenotype.
If a person has one changed q and one unchanged Q copy of a gene, and they do not have the condition associated with that gene change, they are said to be a carrier of that condition. The condition is said to have a recessive inheritance pattern — it is not expressed if there is a functioning copy of the gene present.
If two people are carriers Qq of the same recessive genetic condition, there is a 25 per cent or one in four chance that they may both pass the changed copy of the gene on to their child qq, see figure 2.
As the child then does not have an unchanged, fully functioning copy of the gene, they will develop the condition. There is also a 25 per cent chance that each child of the same parents may be unaffected, and a 50 per cent chance that they may be carriers of the condition. Recessive genetic conditions are more likely to arise if two parents are related, although they are still quite rare. Examples of autosomal recessive genetic conditions include cystic fibrosis and phenylketonuria PKU.
Not all genes are either dominant or recessive. Sometimes, each allele in the gene pair carries equal weight and will show up as a combined physical characteristic. No change in genes or DNA is involved. Pass on from one generation to another. Cannot pass on from one generation to another. Red curly hair, Brown eyes. Cycling, Swimming. Acquired traits. Traits acquired by organisms during their lifetime. Not passed from one generation to another.
Inherited traits. Traits controlled by genes. Passed on from one generation to the next. Somatics is variable. Acquired features developed due to the effects of environmental factors, the use and disguise of organs, and special conscious efforts. Throughout an individual's lifetime, these features develop, and that individual's with death.
Example: learning dance, music, and so on, and the muscular body of a wrestler. Those are variations in genetics. Inherited features evolve due to genetic material rearrangement and mutation.
One was that an innate trait might be defined as a trait an organism will manifest in the normal course of development. But Stich himself offered a counterexample to this analysis: universally held beliefs, such as the belief that water quenches thirst, will count as innate traits on this analysis, which seems counterintuitive Stich , p. Ariew suggests that Stich's analysis confuses evidence for innateness with innateness itself.
Universality is evidence for the existence of a particular kind of developmental mechanism Ariew , p. A similar analysis was independently suggested by Stich , 13— Stich's suggestion has been elaborated and defended by Muhammad Ali Khalidi who like Stich seems not to have encountered Lorenz's work Khalidi ; Khalidi Both Stich and Khalidi restrict the analysis to innate cognitive traits, although it seems clear from Lorenz's work that it can be made general.
Khalidi , Khalidi admits that severe difficulties stand in the way of actually measuring the information content of developmental environments and capacities. He suggests, however, that scientists have rough-and-ready ways to assess the informational gap, using various forms of deprivation experiment see Section 1 above. It is unclear whether Khalidi would endorse Lorenz's analysis of information and of the significance of the deprivation experiment.
The deprivation experiment is designed to eliminate just those factors that could explain the trait's functional adjustment to the environment.
Khalidi makes no reference to the adaptive value of innate traits, and like Stich he thinks that the idea of innateness should be applicable to disease phenotypes as well as to functional phenotypes Khalidi , But Khalidi's idea of an informational gap between the developmental environment and the innate trait seems rather problematic in the case of innate diseases.
What information is manifest in a child born anencephalic and thus, presumably, with no cognitive traits at all? This concept was introduced by the influential mid th century embryologist and theoretical biologist Conrad H. Waddington ; ; ; Developmental canalization was part of a broader vision of how an organism develops from the fertilized egg. Many features of the phenotype are explained by the dynamical properties of that developmental system as a whole, rather than by the influence of one or a few specific alleles.
Thus, for example, Waddington sought to explain one of the major biological discoveries of his day — the fact that extreme phenotypic uniformity can be observed in many wild populations despite extensive genetic variation in those same populations — by appealing to the global dynamics of developmental systems.
A genetically canalized developmental system takes development to the same endpoint from many different genetic starting points. The development of wild-type phenotypes can thus be buffered against genetic variation. Figure 4. The state space is depicted as a surface, each point of which represents a phenotype.
The genetic parameters are depicted as pegs that pull on the surface and thus determine its contours. Epistatic interactions between genetic loci are represented by links between the strings by which those loci pull on the surface. Waddington intended this diagram to make vivid the idea that the effect of a change at one genetic locus depends upon the states of all the other genetic loci, since it is all the loci together which determine the shape of the landscape.
The phenotypic impact of a genetic change is not proportional to the magnitude of the genomic change, but depends on the structure of the developmental system. Furthermore, the phenotypic difference produced by a genetic difference is not explained by that genetic difference in itself, but by how that change interacts with the rest of the developmental system. This picture retains considerably validity in the light of contemporary developmental genetics.
A phenotypic outcome is environmentally canalised if those features of the surface which direct development to that endpoint are relatively insensitive to the manipulation of the environmental parameters. A phenotypic outcome is genetically canalised if those features of the surface which direct development to that endpoint are relatively insensitive to the manipulation of the genetic parameters.
Ariew proposes to identify innateness with environmental canalization. Innateness-as-canalization is a matter of degree. A trait is more innate the more environmental parameters its development is buffered against and the wider the range of variation in those parameters against which it is buffered.
Griffiths and Machery have offered a counterexample to Ariew's analysis Griffiths and Machery The developmental psychobiologist Celia Moore showed that the spinal cord nuclei of male rats differ from those of female rats in ways that allow the male to use his penis during copulation Moore ; Moore These neural differences result from differences in gene expression in the developing spinal cord of the rat pup, which in turn result from differences in the amount of licking of the genital area by the mother, which in turn results from greater expression in male pups of a chemical that elicits maternal licking.
According to Ariew's characterization of innateness as canalization, these experiments show that the rat's ability to copulate is not innate:. The rat's ability to copulate depends on an environmental condition that is found everywhere the system develops and so, according to Ariew, it is not innate. But intuitively the rat's ability to copulate is innate. Griffiths and Machery argue that this intuition results from the fact that the ability to copulate is an evolutionary adaptation and universal in male rats.
Additional counterexamples can be constructed using this formula. However, Ariew has argued, and his critics accept, that the existence of intuitive counterexamples is not really to the point. Instead, the analysis is meant to explicate a research strategy used by scientists like Chomsky. According to Ariew, canalised development is the hallmark of the development of these paradigmatically biological traits, and the research programs of scientists like Chomsky should be seen as attempts to demonstrate the canalised development of psychological traits.
Other recent contributors to the philosophical literature on innateness have adopted a similar methodological stance. The idea of a closed process remains in need of further elaboration. Mallon and Weinberg themselves are concerned about how to individuate developmental processes. They do not want early, general phases of development like the closure of the neural tube to count as part of the development of specific traits like language.
Another significant hurdle for the account is to provide individuation criteria for developmental outcomes. If we attend to the details of the nerve ganglia of the rat's spinal cord, different outcomes can be distinguished, resulting from different amounts of maternal licking and it becomes an open process. Meaney and collaborators Meaney a; Meaney b and see below. Fiona Cowie and Richard Samuels have taken a rather different approach to the innateness concept.
Samuels has suggested that this is the best explication of the concept of innateness in contemporary neo-nativist psychology. Primitivism becomes a more substantive thesis if it is linked to an account of the nature of psychological explanation, or perhaps of psychological explanation as conceived in the neo-nativist tradition.
Ariew suggests that innateness guides research by embodying a strategy of investigating psychological traits as if they were paradigmatically biological traits like hearts and hair.
Cowie and Samuels suggest that innateness guides research by embodying a strategy of not investigating a trait as if it were a paradigmatically psychological trait like a belief or a phobia, but instead treating it as a boundary condition in psychological explanations of related traits.
The incorporation of Lehrman's critique of Lorenz into the ethological tradition had a lasting impact on animal behaviour research. After a half-century of research on the development of birdsong the doyen of researchers in that field, Peter Marler sums up his view of innateness like this:. Other leading animal behaviour researchers see even this casual use of the distinction as pernicious. They judge eight of these to be both genuinely independent definitions and potentially valuable scientific constructs Mameli and Bateson , p.
Several recent philosophical defenders of the innateness concept suggest in a spirit of common sense that whatever the limitations of the concept, traits can at least be placed along a rough continuum of dependence on the environment e.
Ariew ; Mallon and Weinberg ; Khalidi But this does not seem like common sense to many scientists who actually study behavioral development.
Developmental psychobiology is a field that grew out of the research tradition of which Lehrman was part for a textbook treatment see Michel and Moore ; two excellent popular introductions are Bateson and Martin , and Moore The consensus in this field is that experimental research on the development of a trait typically reveals sensitive dependence on environmental parameters.
These parameters are highly varied, and they interact non-additively with genetic parameters. Developmental psychobiologists reject a basic idea at the heart of much discussion of innateness, which is that evolution makes development reliable by making it insensitive to environmental parameters. Instead, they argue that evolution often makes development reliable by stabilizing environmental parameters at the right value or by exploiting pre-existing environmental regularities.
West and King and their collaborators have conducted a long term study of the ontogenetic niche of the brown-headed cowbird Molothrus Ater West and King ; West and King ; West, King et al.
Cowbirds are obligate nest parasites like cuckoos and do not hear their parents sing as they grow up. West and King showed that, amongst other processes, male song is shaped by feedback from female cowbirds, whose wing stroking and gaping displays in response to the songs they prefer are strong reinforcers for males.
Female song preferences are themselves subject to social influences. As a result of these and other processes cowbirds reliably transmit not only species-typical song, but also the regional song dialects typical of birds that acquire their songs as a result of exposure to parental song.
In stark contrast to the suggestions of the philosophers discussed in Section 4. In many species, of course, the stabilization of the parameters of the ontogenetic niche is achieved through parental care, as we saw in the case of the development of penile reflexes in the rat in Section 4.
But parental care can also be used as a mechanism of adaptive phenotypic plasticity. Michael Meaney and collaborators' account of the role of parental care in the development of temperament in rats is a good exemplar of this phenomenon. Cross-fostering BALBc pups to mothers of the more laid-back C57 strain removes the differences between the two strains. Meaney and collaborators show how the amount of licking and arched-back nursing which pups receive from their mother regulates gene expression so as to direct the development of the pup's brain Meaney, Although the phenotypes of these inbred laboratory strains are constant, it is plausible that in wild rats maternal behavior reflects the mother's stress levels.
We might guess that the rat pup will respond to indicators of environmental quality, and we might guess that the mother's behavior is a useful source of information on this topic, but not that the information resides in whether the mother arches her back during suckling.
Non-obvious parameters are typically overlooked in deprivation experiments designed to establish that a trait is innate, but are often revealed by positive efforts to understand how behaviour develops Gottlieb Natural selection does not select for mechanisms which buffer traits against variation in the environment unless variation of that kind regularly occurs in the environments in which the species lives.
In fact, any buffering mechanism which is not actively being used will tend to decay by mutation. One famous example is the inability of humans and their relatives to synthesise ascorbic acid vitamin C. The ascorbic acid synthesis pathway was disabled by mutation during the long period in which our fruit-eating ancestors had no chance of developing vitamin C deficiences Jukes and King It is part of folkbiology that some traits are expressions of the inner nature of animals and plants, whilst other traits result from the influence of the environment.
Echoing the traditional critique of the innateness concept in animal behaviour research, Griffiths and collaborators argue that folkbiology conflates the issues of whether a trait is typical of the species, whether it is part of the design of the species, and whether its development is insensitive to the environment. Attempts to redefine innateness in a way that stresses just one of its many aspects and thus makes it a useful scientific construct have been and will continue to be stymied by the fact that the broad concept of innateness is part of our evolved psychological equipment.
It may be that resolving the disputes between the many competing analyses of the innateness concept outlined in Section 4 will require taking these claims more seriously and looking in detail at how nativist researchers use the idea of innateness, perhaps through detailed case studies. Philosophical scepticism about innateness draws on a longstanding tradition of scepticism in developmental psychobiology.
Philosophical defenders of the distinction would benefit from looking at these cases, in which the distinction is purportedly inapplicable or unhelpful, in addition to the cases used by neo-nativists to exemplify the distinction. One thing seems clear, which is that efforts to clarify the distinction in psychology by appeal to the underlying genetics have not been successful. Once again, this suggests that the distinction may be best understood via its actual use in psychological research.
Innateness and heritability 3. Innateness and genetics 4. Recent philosophical analyses of the concept of innateness 4. Lehrman summarised his position at a later date: Natural selection acts to select genomes that, in a normal developmental environment, will guide development into organisms with the relevant adaptive characteristics.
But the path of development from the zygote stage to the phenotypic adult is devious, and includes many developmental processes, including, in some cases, various aspects of experience. Lehrman , 36 Lehrman was particularly critical of the use of the deprivation experiment to infer that a certain trait is innate simpliciter , rather than merely that the factors controlled for in the experiment are not needed for the development of that trait.
Innateness and heritability Popular discussion of whether psychological and behavioural traits are innate is bedevilled by the conflation of this issue with whether psychological and behavioural traits are heritable. Figure 1. Figure 2. Purely additive interaction between genotype and environment In perhaps the most famous paper on this topic the geneticist Richard Lewontin argued that actual norms of reaction are likely to be non-additive Figure 3.
Figure 3. According to Ariew's characterization of innateness as canalization, these experiments show that the rat's ability to copulate is not innate: Distinguish between two reasons why the trait appears invariantly in an environmental range: the first, because an environmental condition is developmentally required yet is found everywhere the system develops; the second, because the system develops independently of the environmental condition.
Innateness should be identified with the second sort of invariance, not the first. Ariew , 10 The rat's ability to copulate depends on an environmental condition that is found everywhere the system develops and so, according to Ariew, it is not innate.
The habit of labeling behaviors in this fashion is so deep-rooted that we will probably never succeed in eradicating it. Marler, , 31 Other leading animal behaviour researchers see even this casual use of the distinction as pernicious.
Bibliography Ariew, A. Ariew, A. Hardcastle ed. Handbook of the Philosophy of Science , M. Matthen and C. Stevens eds. Bateson, P.
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