Peppered moth
Encyclopedia
The peppered moth is a temperate species of night-flying moth
. Peppered moth evolution
is often used by educators as an example of natural selection
.
(Heilongjiang, Jilin, Inner Mongolia, Beijing, Hebei, Shanxi, Shandong, Henan, Shaanxi, Ningxia, Gansu, Qinghai, Xinjiang, Fujian, Sichuan, Yunnan,
Tibet), Russia
, Mongolia
, Japan
, North Korea
, South Korea
, Nepal
, Kazakhstan
, Kirghizstan, Turkmenistan
, Georgia
, Azerbaijan
, Armenia
, Europe
and North America
.
In Britain
and Ireland
, the peppered moth is univoltine
(i.e., it has one generation per year), whilst in south-eastern North America
it is bivoltine (two generations per year). The lepidoptera
n life cycle
consists of four stages: ova (eggs), several larva
l instar
s (caterpillar
s), pupa
e, which overwinter live in the soil, and imagines
(adults). During the day, the moths typically rest on trees, where they are preyed on by birds.
The caterpillar is a twig mimic
, varying in colour between green and brown. It goes into the soil late in the season, where it pupates in order to spend the winter. The imagines emerge from the pupae between late May and August, the males slightly before the females (this is common and expected from sexual selection
). They emerge late in the day and dry their wings before flying that night.
The males fly every night of their lives in search of females, whereas the females only fly on the first night. Thereafter, the females release pheromone
s to attract males. Since the pheromone is carried by the wind, males tend to travel up the concentration gradient, i.e., toward the source. During flight, they are subject to predation by bat
s. The males guard the female from other males until she lays the eggs. The female lays about 2,000 pale-green ovoid eggs about 1 mm in length into crevices in bark with her ovipositor
.
A mating pair or a lone individual will spend the day hiding from predators, particularly birds. In the case of the former, the male stays with the female to ensure paternity. The best evidence for resting positions is given by data collected by the peppered moth researcher Michael Majerus
, and it is given in the accompanying charts. These data were originally published in Howlett and Majerus (1987), and an updated version published in Majerus (1998), who concluded that the moths rest in the upper part of the trees. Majerus notes:
From their original data, Howlett and Majerus (1987) concluded that peppered moths generally rest in unexposed positions, using three main types of site. Firstly, a few inches below a branch-trunk joint on a tree trunk where the moth is in shadow; secondly, on the underside of branches and thirdly on foliate twigs. The above data would appear to support this.
Further support for these resting positions is given from experiments watching captive moths taking up resting positions in both males (Mikkola, 1979; 1984) and females (Liebert and Brakefield, 1987).
Majerus, et al., (2000) have shown that peppered moths are cryptically camouflaged against their backgrounds when they rest in the boughs of trees. It is clear that in human visible wavelength
s, typica are camouflaged against lichen
s and carbonaria against plain bark
. However, birds are capable of seeing ultraviolet
light that humans cannot see. Using an ultraviolet-sensitive video camera, Majerus et al. showed that typica reflect ultraviolet light in a speckled fashion and are camouflaged against crustose lichens common on branches, both in ultraviolet and human-visible wavelengths. However, typica are not as well camouflaged against foliose lichens common on tree trunks; though they are camouflaged in human wavelengths, in ultraviolet wavelengths, foliose lichens do not reflect ultraviolet light.
During an experiment in Cambridge
over the seven years 2001–2007 Majerus noted the natural resting positions of peppered moths, and of the 135 moths examined over half were on tree branches, mostly on the lower half of the branch, 37% were on tree trunks, mostly on the north side, and only 12.6% were resting on or under twigs.
and non-melanic morphs of the peppered moth. These are controlled genetically. A particular morph can be indicated in a standard way by following the species name in the form "morpha morph name".
It is a common mistake to confuse the name of the morph with that of the species
or subspecies
, hence mistakes such as "Biston carbonaria" and "Biston betularia carbonaria". This might lead to the erroneous belief that speciation
was involved in the observed evolution of the peppered moth. This is not the case; individuals of each morph interbreed and produce fertile offspring with individuals of all other morphs; hence there is only one peppered moth species.
By contrast, different subspecies of the same species can theoretically interbreed with one another and will produce fully fertile and healthy offspring but in practice do not, as they live in different regions or reproduce in different seasons. Full-fledged species are either unable to produce fertile and healthy offspring, or do not recognize each other's courtship signals, or both.
In continental Europe, there are three morphs: morpha typica, the typical white morph (also known as "morpha betularia"), morpha carbonaria, the melanic black morph (also previously known as "morpha doubledayaria"), and morpha medionigra, an intermediate semi-melanic morph. European breeding experiments have shown that in Biston betularia betularia, the allele
for melanism producing morpha carbonaria is controlled by a single locus
. The melanic allele is dominant to the non-melanic allele. This situation is, however, somewhat complicated by the presence of three other alleles that produce indistinguishable morphs of morpha medionigra. These are of intermediate dominance, but this is not complete (Majerus, 1998).
In Britain, the typical white speckled morph is known as morpha typica, the melanic morph is morpha carbonaria, and the intermediate phenotype
is morpha insularia.
In North America, the melanic black morph is morpha swettaria. In Biston betularia cognataria, the melanic allele (producing morpha swettaria) is similarly dominant to the non-melanic allele. There are also some intermediate morphs. In Japan
, no melanic morphs have been recorded; they are all morpha typica.
At present, the precise molecular genetics
and biochemistry
of the melanism in this species remains unknown. True (2003) has reviewed this and suggests work based on candidate gene
s from other insects such as the fruit fly Drosophila melanogaster
. In any case, it is rather likely that the underlying mechanism is not overly complex and, as indicated above, does not involve very many gene
s and allele
s: Unlike for example the variation seen in human skin color
, Peppered Moth morphs are not clinal
and can generally be readily distinguished from another.
The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflage
d them against the light-coloured trees and lichens upon which they rested. However, due to widespread pollution during the Industrial Revolution
in England, many of the lichens died out, and the trees which peppered moths rested on became blackened by soot
, causing most of the light-coloured moths, or typica, to die off due to predation. At the same time, the dark-coloured, or melanic, moths, carbonaria, flourished because of their ability to hide on the darkened trees.
Since then, with improved environmental standards, light-colored peppered moths have again become common, but the dramatic change in the peppered moth's population has remained a subject of much interest and study. This has led to the coining of the term "industrial melanism
" to refer to the genetic darkening of species in response to pollutants. As a result of the relatively simple and easy-to-understand circumstances of the adaptation, the peppered moth has become a common example used in explaining or demonstrating natural selection
to laypeople and classroom students.
The first carbonaria morph was recorded by Edleston in Manchester in 1848, and over the subsequent years it increased in frequency. Predation experiments, particularly by Bernard Kettlewell
, established that the agent of selection was birds who preyed on the carbonaria morph.
Jonathan Wells is one of a number of creationists
who have criticized the use of peppered moth melanism as an example of evolution in action. In his book Icons of Evolution
, Wells alleges that peppered moth studies, and in particular Kettlewell's experiments, were erroneous. Similarly, in 2002 Judith Hooper
repeatedly implied fraud and error in Kettlewell's experiments in her book titled Of moths and men
. Despite some valid criticisms of the early experiments, there has been no evidence of fraud. Subsequent experiments and observations have supported the initial explanation of the phenomenon. But the problem, according to the Young Earth creationist
Dr. Tommy Mitchell of Answers in Genesis
, is this only represents a case of natural selection, and not of evolution, as a population of a "kind" of moth turned into simply a population of another "kind" of moth. While it is true that this example shows natural selection causing microevolution
within a species, it demonstrates rapid and obvious adaptiveness with such change.
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
. Peppered moth evolution
Peppered moth evolution
The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon...
is often used by educators as an example of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
.
Distribution
Biston betularia is found in ChinaChina
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
(Heilongjiang, Jilin, Inner Mongolia, Beijing, Hebei, Shanxi, Shandong, Henan, Shaanxi, Ningxia, Gansu, Qinghai, Xinjiang, Fujian, Sichuan, Yunnan,
Tibet), Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
, South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
, Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...
, Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
, Kirghizstan, Turkmenistan
Turkmenistan
Turkmenistan , formerly also known as Turkmenia is one of the Turkic states in Central Asia. Until 1991, it was a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic . Turkmenistan is one of the six independent Turkic states...
, Georgia
Georgia (country)
Georgia is a sovereign state in the Caucasus region of Eurasia. Located at the crossroads of Western Asia and Eastern Europe, it is bounded to the west by the Black Sea, to the north by Russia, to the southwest by Turkey, to the south by Armenia, and to the southeast by Azerbaijan. The capital of...
, Azerbaijan
Azerbaijan
Azerbaijan , officially the Republic of Azerbaijan is the largest country in the Caucasus region of Eurasia. Located at the crossroads of Western Asia and Eastern Europe, it is bounded by the Caspian Sea to the east, Russia to the north, Georgia to the northwest, Armenia to the west, and Iran to...
, Armenia
Armenia
Armenia , officially the Republic of Armenia , is a landlocked mountainous country in the Caucasus region of Eurasia...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Ecology and life cycle
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
, the peppered moth is univoltine
Voltinism
Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is particularly in use in sericulture, where silkworm varieties vary in their voltinism....
(i.e., it has one generation per year), whilst in south-eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
it is bivoltine (two generations per year). The lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
n life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
consists of four stages: ova (eggs), several larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s (caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s), pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e, which overwinter live in the soil, and imagines
Imago
In biology, the imago is the last stage of development of an insect, after the last ecdysis of an incomplete metamorphosis, or after emergence from the pupa where the metamorphosis is complete...
(adults). During the day, the moths typically rest on trees, where they are preyed on by birds.
The caterpillar is a twig mimic
Mimic
In evolutionary biology, mimicry is the similarity of one species to another which protects one or both. This similarity can be in appearance, behaviour, sound, scent and even location, with the mimics found in similar places to their models....
, varying in colour between green and brown. It goes into the soil late in the season, where it pupates in order to spend the winter. The imagines emerge from the pupae between late May and August, the males slightly before the females (this is common and expected from sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
). They emerge late in the day and dry their wings before flying that night.
The males fly every night of their lives in search of females, whereas the females only fly on the first night. Thereafter, the females release pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s to attract males. Since the pheromone is carried by the wind, males tend to travel up the concentration gradient, i.e., toward the source. During flight, they are subject to predation by bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s. The males guard the female from other males until she lays the eggs. The female lays about 2,000 pale-green ovoid eggs about 1 mm in length into crevices in bark with her ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
.
Resting behaviour
Michael Majerus
Michael Eugene Nicolas Majerus was a geneticist and Professor of Ecology at Clare College, Cambridge, an enthusiast who became a world authority in his field of evolutionary biology. He was widely noted for his work on moths and ladybirds and as an advocate of the science of evolution...
, and it is given in the accompanying charts. These data were originally published in Howlett and Majerus (1987), and an updated version published in Majerus (1998), who concluded that the moths rest in the upper part of the trees. Majerus notes:
Creationist critics of the peppered moth have often pointed to a statement made by Clarke et al. (1985): "... In 25 years we have only found two betularia on the tree trunks or walls adjacent to our traps, and none elsewhere". The reason now seems obvious. Few people spend their time looking for moths up in the trees. That is where peppered moths rest by day.
From their original data, Howlett and Majerus (1987) concluded that peppered moths generally rest in unexposed positions, using three main types of site. Firstly, a few inches below a branch-trunk joint on a tree trunk where the moth is in shadow; secondly, on the underside of branches and thirdly on foliate twigs. The above data would appear to support this.
Further support for these resting positions is given from experiments watching captive moths taking up resting positions in both males (Mikkola, 1979; 1984) and females (Liebert and Brakefield, 1987).
Majerus, et al., (2000) have shown that peppered moths are cryptically camouflaged against their backgrounds when they rest in the boughs of trees. It is clear that in human visible wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s, typica are camouflaged against lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s and carbonaria against plain bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
. However, birds are capable of seeing ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light that humans cannot see. Using an ultraviolet-sensitive video camera, Majerus et al. showed that typica reflect ultraviolet light in a speckled fashion and are camouflaged against crustose lichens common on branches, both in ultraviolet and human-visible wavelengths. However, typica are not as well camouflaged against foliose lichens common on tree trunks; though they are camouflaged in human wavelengths, in ultraviolet wavelengths, foliose lichens do not reflect ultraviolet light.
During an experiment in Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...
over the seven years 2001–2007 Majerus noted the natural resting positions of peppered moths, and of the 135 moths examined over half were on tree branches, mostly on the lower half of the branch, 37% were on tree trunks, mostly on the north side, and only 12.6% were resting on or under twigs.
Morphs
There are several melanicMelanism
Melanism is an undue development of dark-colored pigment in the skin or its appendages, and the opposite of albinism. It is also the medical term for black jaundice.The word is deduced from the , meaning black pigment....
and non-melanic morphs of the peppered moth. These are controlled genetically. A particular morph can be indicated in a standard way by following the species name in the form "morpha morph name".
It is a common mistake to confuse the name of the morph with that of the species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
or subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
, hence mistakes such as "Biston carbonaria" and "Biston betularia carbonaria". This might lead to the erroneous belief that speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
was involved in the observed evolution of the peppered moth. This is not the case; individuals of each morph interbreed and produce fertile offspring with individuals of all other morphs; hence there is only one peppered moth species.
By contrast, different subspecies of the same species can theoretically interbreed with one another and will produce fully fertile and healthy offspring but in practice do not, as they live in different regions or reproduce in different seasons. Full-fledged species are either unable to produce fertile and healthy offspring, or do not recognize each other's courtship signals, or both.
In continental Europe, there are three morphs: morpha typica, the typical white morph (also known as "morpha betularia"), morpha carbonaria, the melanic black morph (also previously known as "morpha doubledayaria"), and morpha medionigra, an intermediate semi-melanic morph. European breeding experiments have shown that in Biston betularia betularia, the allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
for melanism producing morpha carbonaria is controlled by a single locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
. The melanic allele is dominant to the non-melanic allele. This situation is, however, somewhat complicated by the presence of three other alleles that produce indistinguishable morphs of morpha medionigra. These are of intermediate dominance, but this is not complete (Majerus, 1998).
In Britain, the typical white speckled morph is known as morpha typica, the melanic morph is morpha carbonaria, and the intermediate phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
is morpha insularia.
In North America, the melanic black morph is morpha swettaria. In Biston betularia cognataria, the melanic allele (producing morpha swettaria) is similarly dominant to the non-melanic allele. There are also some intermediate morphs. In Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, no melanic morphs have been recorded; they are all morpha typica.
At present, the precise molecular genetics
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
and biochemistry
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
of the melanism in this species remains unknown. True (2003) has reviewed this and suggests work based on candidate gene
Candidate gene
A candidate gene is a gene, located in a chromosome region suspected of being involved in the expression of a trait such as a disease, whose protein product suggests that it could be the gene in question...
s from other insects such as the fruit fly Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
. In any case, it is rather likely that the underlying mechanism is not overly complex and, as indicated above, does not involve very many gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s and allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s: Unlike for example the variation seen in human skin color
Human skin color
Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...
, Peppered Moth morphs are not clinal
Cline (population genetics)
In biology, an ecocline or simply cline describes an ecotone in which a series of biocommunities display continuous gradient...
and can generally be readily distinguished from another.
Evolution
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
d them against the light-coloured trees and lichens upon which they rested. However, due to widespread pollution during the Industrial Revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
in England, many of the lichens died out, and the trees which peppered moths rested on became blackened by soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
, causing most of the light-coloured moths, or typica, to die off due to predation. At the same time, the dark-coloured, or melanic, moths, carbonaria, flourished because of their ability to hide on the darkened trees.
Since then, with improved environmental standards, light-colored peppered moths have again become common, but the dramatic change in the peppered moth's population has remained a subject of much interest and study. This has led to the coining of the term "industrial melanism
Melanism
Melanism is an undue development of dark-colored pigment in the skin or its appendages, and the opposite of albinism. It is also the medical term for black jaundice.The word is deduced from the , meaning black pigment....
" to refer to the genetic darkening of species in response to pollutants. As a result of the relatively simple and easy-to-understand circumstances of the adaptation, the peppered moth has become a common example used in explaining or demonstrating natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
to laypeople and classroom students.
The first carbonaria morph was recorded by Edleston in Manchester in 1848, and over the subsequent years it increased in frequency. Predation experiments, particularly by Bernard Kettlewell
Bernard Kettlewell
Henry Bernard Davis Kettlewell was a British geneticist, lepidopterist and medical doctor, who carried out research into the influence of industrial melanism on natural selection in moths, showing why moths are darker in polluted areas.-Early life:Kettlewell was born in Howden, Yorkshire, and...
, established that the agent of selection was birds who preyed on the carbonaria morph.
Jonathan Wells is one of a number of creationists
Creationism
Creationism is the religious beliefthat humanity, life, the Earth, and the universe are the creation of a supernatural being, most often referring to the Abrahamic god. As science developed from the 18th century onwards, various views developed which aimed to reconcile science with the Genesis...
who have criticized the use of peppered moth melanism as an example of evolution in action. In his book Icons of Evolution
Icons of Evolution
Icons of Evolution is a book by the intelligent design advocate and fellow of the Discovery Institute, Jonathan Wells, which also includes a 2002 video companion. In the book, Wells criticized the paradigm of evolution by attacking how it is taught...
, Wells alleges that peppered moth studies, and in particular Kettlewell's experiments, were erroneous. Similarly, in 2002 Judith Hooper
Judith Hooper
Judith Hooper is an American journalist.Hooper has worked as an editor and writer for the magazine Omni. With her husband, Dick Teresi, she co-wrote the books The Three-Pound Universe and Would the Buddha Wear a Walkman? A Catalogue of Revolutionary Tools for Higher Consciousness...
repeatedly implied fraud and error in Kettlewell's experiments in her book titled Of moths and men
Of Moths and Men
Of Moths and Men is a controversial book by the journalist Judith Hooper about the Oxford University ecological genetics school led by E.B. Ford. The book specifically concerns Bernard Kettlewell's experiments on the peppered moth which were intended as experimental validation of evolution...
. Despite some valid criticisms of the early experiments, there has been no evidence of fraud. Subsequent experiments and observations have supported the initial explanation of the phenomenon. But the problem, according to the Young Earth creationist
Young Earth creationism
Young Earth creationism is the religious belief that Heavens, Earth, and all life on Earth were created by direct acts of the Abrahamic God during a relatively short period, sometime between 5,700 and 10,000 years ago...
Dr. Tommy Mitchell of Answers in Genesis
Answers in Genesis
Answers in Genesis is a non-profit Christian apologetics ministry with a particular focus on supporting Young Earth creationism and a literal interpretation of the Book of Genesis. The organization has offices in the United Kingdom and the United States...
, is this only represents a case of natural selection, and not of evolution, as a population of a "kind" of moth turned into simply a population of another "kind" of moth. While it is true that this example shows natural selection causing microevolution
Microevolution
Microevolution is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection , gene flow, and genetic drift....
within a species, it demonstrates rapid and obvious adaptiveness with such change.
External links
- Bruce GrantBruce GrantProfessor Bruce S. Grant is emeritus professor of biology at the College of William and Mary. He has a particular research interest in the peppered moth. He is a defender of the teaching of evolution and has criticized creationist Jonathan Wells, who has cited his work, as "dishonest."Grant has a...
has written several papers on melanism in the peppered moth which are listed on his home page. - Online lecture: "The rise and fall of the melanic Peppered Moth" presented by Laurence Cook.
- The Peppered Moth: Decline of a Darwinian Disciple. This is the transcript of Michael MajerusMichael MajerusMichael Eugene Nicolas Majerus was a geneticist and Professor of Ecology at Clare College, Cambridge, an enthusiast who became a world authority in his field of evolutionary biology. He was widely noted for his work on moths and ladybirds and as an advocate of the science of evolution...
' lecture delivered to the British Humanist AssociationBritish Humanist AssociationThe British Humanist Association is an organisation of the United Kingdom which promotes Humanism and represents "people who seek to live good lives without religious or superstitious beliefs." The BHA is committed to secularism, human rights, democracy, egalitarianism and mutual respect...
on Darwin DayDarwin DayDarwin Day is a recently instituted celebration intended to commemorate the anniversary of the birth of Charles Darwin on February 12, 1809. The day is used to highlight Darwin's contribution to science and to promote science in general.-History:...
2004. - The Peppered Moth: The Proof of Darwinian Evolution. This is the transcript of Majerus' lecture given at the European Society for Evolutionary BiologyEuropean Society for Evolutionary BiologyThe European Society for Evolutionary Biology was founded in 1987. It is publishing the Journal of Evolutionary Biology, organises meetings and biannually awards a John Maynard Smith Prize.As of 2007 its president is Isabelle Olivieri....
meeting on 23 August 2007. The accompanying powerpoint presentation is also available as a pdf file. - An interactive game to simulate how evolution works with Biston betularia