FACTOID # 30: If Alaska were its own country, it would be the 26th largest in total area, slightly larger than Iran.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Sexually dimorphic
Female (left) and male Common Pheasant, illustrating the dramatic difference in form between the sexes
Female (left) and male Common Pheasant, illustrating the dramatic difference in form between the sexes

Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. Male and female pheasant (Phasianus colchicus) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Male and female pheasant (Phasianus colchicus) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Binomial name Phasianus colchicus Linnaeus, 1758 The Common Pheasant (Phasianus colchicus) is a gamebird in the pheasant family Phasianidae of the order Galliformes, gallinaceous birds. ... Look up Sex on Wiktionary, the free dictionary A sex is one of two specimen categories of species that recombine their genetic material in order to reproduce, a process called genetic recombination. ... In biology, the most commonly used definition of species was first coined by Ernst Mayr. ...

Contents


Examples of sexual dimorphism

In some species, including many mammals, the male is larger than the female. In others, such as some spiders and many insect species, the female is larger than the male; a larger size is advantageous for carrying or laying eggs. Other sex-specific differences include color (most birds), size or presence of parts of the body used in struggles for dominance, such as horns, antlers, and tusks; size of the eyes (bees); possession of stings (various kinds of bees), and different thresholds for certain behaviors (aggression, infant care, etc.). Orders Subclass Embrithopoda (extinct) Subclass Creodonta (extinct) Hyaenodontidae Oxyaenidae Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Placentalia Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Dermoptera Desmostylia (extinct) Hyracoidea Insectivora Lagomorpha Macroscelidea Perissodactyla Pholidota Primates Proboscidea Rodentia Scandentia Sirenia Tubulidentata Xenarthra Subclass Marsupialia Dasyuromorphia Didelphimorphia Diprotodontia Microbiotheria Notoryctemorphia... Male symbol Male is the sex of an organism, or a part of an organism, which produces sperm. ... Female symbol Female is the sex of an organism, or a part of an organism, which produces egg cells. ... Suborders Araneomorphae Mesothelae Mygalomorphae See the taxonomy section for families Spiders are invertebrate animals that produce silk, have eight legs and no wings. ... Classes & Orders Subclass: Apterygota Orders Archaeognatha (Bristletails) Thysanura (Silverfish) Monura - extinct Subclass: Pterygota Orders Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Infraclass: Neoptera Orders Blattodea (cockroaches) Isoptera (termites) Mantodea (mantids) Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, etc) Phasmatodea (walking sticks) Embioptera (webspinners) Zoraptera... Orders Many - see section below. ... Families Andrenidae Apidae Colletidae Halictidae Heterogynaidae Megachilidae Melittidae Oxaeidae Sphecidae Stenotritidae bee or bees, see bee (disambiguation). ...


Sexual dimorphism is particularly apparent in game birds such as the pheasant, with males possessing bright plumage while females are usually a drab brown. Some cases of sexual dimorphism in birds are so striking that males and females of a same species were originally taken to be members of entirely different species, as in the case of the eclectus parrot, where the male is predominantly green with an orange beak and the female mainly scarlet with a black beak. Game is any animal hunted for food. ... Genera Ithaginis Catreus Rheinartia Crossoptilon Lophura Argusianus Pucrasia Syrmaticus Chrysolophus Phasianus † See also partridge, quail Pheasants are a group of large birds in the order Galliformes. ... Binomial name Eclectus roratus (Statius Muller, 1776) The Eclectus Parrot (Eclectus roratus) is a parrot native to the Solomon Islands, New Guinea, northeastern Australia and the Maluku Islands (Moluccas). ...


Another striking example was the Huia, a recently-extinct New Zealand bird. The male's bill was short, sharp and stout while the female's was long, thin and crescent shaped. One purpose of the dimorphism allowed the male to chisel the entrance to beetle grub holes in living trees, thereby giving the female further reach to pull out the grub that they may then share. Huia had been little studied by Western naturalists before they were driven to extinction and other purposes of the dimorphism had yet to be ascertained. Binomial name Heteralocha acutirostris (Gould, 1837) The Huia (Heteralocha acutirostris) was a bird that was native to New Zealand. ... Binomial name Heteralocha acutirostris (Gould, 1837) The Huia (Heteralocha acutirostris) was a bird that was native to New Zealand. ...


One of the most extreme examples of sexual dimorphism is found in the small worms of the genus Osedax, which live on whale falls. The females feed on the whale bones. The males live inside the females and do not develop past their larval stage except to produce large amounts of sperm. Species Osedax frankpressi Osedax rubiplumus The osedax are a genus of whalebone-eating siboglinids (deep sea worms), first discovered in Monterey Bay, California, in June 2004. ... Whale fall is the term used for a whale carcass that has fallen to the ocean floor. ...


Sexual dimorphism in humans

Stylised illustration of humans showing sexual dimorphism. The male is on the left.
Stylised illustration of humans showing sexual dimorphism. The male is on the left.

Sexual dimorphism in humans is the subject of much controversy, especially relating to mental ability. (For a discussion, see sex and intelligence.) Human male and female appearances are perceived as different, although Homo sapiens has a low level of sexual dimorphism compared with many other species. The similarity in the sizes of male and female human beings is a good example of how nature often does not make clear divisions. Standard growth curves give a fairly accurate picture of male and female size differences. The overlap is slightly less than 1 standard deviation. The CDC published new American curves in 2000 and it is available online here. Image File history File links Human. ... Image File history File links Human. ... The question about whether the human sexes displayed differences in mental aptitude or cognitive abilities has been studied numerous times in history, often—but not always—coming to the conclusion that men were on the whole more intelligent than women. ... Male symbol Male is the sex of an organism, or a part of an organism, which produces sperm. ... Female symbol Female is the sex of an organism, or a part of an organism, which produces egg cells. ... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ...


For example, the body masses of both male and female humans are approximately normally distributed. In the United States, the mean mass of an adult male is 78.5 kg (173.1 lb), while the adult female mean is 62.0 kg (136.7 lb). However the standard deviation of male body mass is 12.6 kg (27.8 lb), so 10% of adult males are actually lighter than the female average. The normal distribution, also called Gaussian distribution, is an extremely important probability distribution in many fields. ... In mathematics and statistics, the arithmetic mean of a set of numbers is the sum of all the members of the set divided by the number of items in the set. ... KG, Kg or kg may indicate: A Kampfgeschwader, a bomber squadron of the former German Luftwaffe Basketball Player Kevin Garnett An abbreviation for kilogram (always kg) Knight of the Garter, a British decoration Kommanditgesellschaft, German version of a limited partnership Kongo language (ISO 639 alpha-2) An abbreviation for konig... In probability and statistics, the standard deviation is the most commonly used measure of statistical dispersion. ...


There is also sexual dimorphism in the amount and distribution of body hair, with males having more terminal hair, especially on the face, chest and back, and females having more vellus hair, which is less visible. This makes males generally appear more "hairy" than females, but again, the standard distributions of these patterns overlap and some females appear more "hairy" than some males. This may also be linked to neoteny in humans, as vellus hair is a juvenile characteristic. A human female with brown hair. ... Developed hair, which is generally longer, coarser, thicker, and darker than vellus hair. ... Vellus hair is short, fine, peach fuzz body hair. ... Neoteny is a term in developmental biology that describes the retention of juvenile characteristics in the adults of a species and is similar to but not the same as progenesis, which is the attainment of sexual maturity by an organism still in its larval stage, as is found among certain... Vellus hair is short, fine, peach fuzz body hair. ... Juvenile has a number of uses: A juvenile can be an individual organism that has not yet reached its adult form, maturity or size; for humans this is called a child. ...


Biological aspects of sexual dimorphism

The phenomenon of sexual dimorphism is a direct product of evolution by natural selection, in that the struggle for reproductive success drives many male and female organisms down different evolutionary paths. This can produce forms of dimorphism which, on the face of it, would actually seem to disadvantage organisms. For instance, the bright colouration of male game birds makes them highly visible targets for predators, while the drably coloured females are far better equipped to camouflage themselves. Likewise, the antlers of deer and other forms of natural weaponry are very expensive to grow and carry in terms of the energy consumed by the animal in the process. Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ... Anolis caroliensis showing blending camouflage and counter-shading. ...


The answer to this apparent paradox is that, at a biological level, the reproductive success of an organism is often more important than its long-term survival. This is particularly apparent in the case of game birds: a male Common Pheasant in the wild often lives no more than 10 months, with females living twice as long. However, a male pheasant's ability to reproduce depends not on how long he lives but whether females will select him to be their mate. His bright colouration demonstrates to the female that he is fit, healthy and a good choice to father her chicks. Binomial name Phasianus colchicus Linnaeus, 1758 The Common Pheasant (Phasianus colchicus) is a gamebird in the pheasant family Phasianidae of the order Galliformes, gallinaceous birds. ...


In the case of herd animals such as deer, a male deer's reproductive success is directly proportional to the number of sexually receptive females with which he can mate. The males' antlers are an example of a sexually dimorphic weapon with which the males fight each other to establish breeding rights. Again, although they are expensive in terms of personal survival, they ensure that the largest and strongest males will be the most successful in reproducing and thereby ensure that those characteristics are passed on to the next generation. Subfamilies Capreolinae Cervinae Hydropotinae Muntiacinae Defined strictly, a deer is a ruminant mammal belonging to the family Cervidae. ... For the Poet Laureate of Milwaukee, see Antler (Poet). ...


Access to the opposite sex is not the only reason why sexual dimorphism exists. In insects in particular, females are often larger than the males. It is thought that the reason lies in the huge number of eggs that insects lay; a larger body size enables a female insect to lay more eggs. In some cases, sexual dimorphism enables males and females to exploit different food resources, thus increasing their collective ability to find food. Some species of woodpecker have differently-sized and shaped beaks, enabling the sexes to find insects in different layers of a tree's bark. Genera Many, see text. ...


Sexual dimorphism is sometimes quantified by biologists through the dimorphism index, which is usually the ratio between the average adult male mass and average adult female mass. For some species mass is inconvenient to measure, so a similar parameter such as volume is used instead. This index is commonly written as the abbreviation "SSDI", for "sexual size dimorphism index". Species that are typically polygynous tend to have high SSDI ratios, while species that are typically polyandrous tend to have low ratios. A biologist is a scientist devoted to and producing results in biology through the study of organisms. ... In algebra, a ratio is the relationship between two quantities. ... A parameter is a measurement or value on which something else depends. ... Volume, also called capacity, is a quantification of how much space an object occupies. ... Look up abbreviation in Wiktionary, the free dictionary Abbreviation (from Latin brevis short) is strictly a shortening, but more particularly, an abbreviation is a letter or group of letters, taken from a word or words, and employed to represent them for the sake of brevity. ... The term polygyny (Greek: poly many, gynaika woman) is used in related ways in social anthropology and sociobiology. ... In social anthropology and sociobiology, polyandry (Greek: poly many, andros man) means a female forming a stable sexual union with more than one male. ...


Sexual dimorphism is regarded as a classic example of genetic polymorphism, though its underlying mechanism varies in different organisms. It is often controlled by genes on the sexual chromosomes. Figure 1: Chromosome. ...


See also


  Results from FactBites:
 
Theoretical Background (12841 words)
Rice (1984), came to a different conclusion and, in a theoretical analysis of the effect of X-linkage on the evolution of sexual dimorphism, stated that "sex chromosomes facilitate the evolution of sexual dimorphism and that X-linked genes have a predominant role in coding for sexually dimorphic traits".
Sexual selection is thought to operate on males characters in two main ways: male competition where the winning male gains access to more matings, and female choice where the female chooses the male she deems more fit.
Ely, J. and Kurland, J. Spatial autocorrelation, phylogenetic constraints, and the causes of sexual dimorphism in primates.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m