Parallel evolution is the development of a similar trait in different not closely related species (that is in species of a different
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
), but descending from the same ancestor.
For a particular trait, proceeding in each of two lineages from a specified ancestor to a later descendant, parallel and
convergentConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
evolutionary trends can be strictly defined and clearly distinguished from one another.
When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not.
When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective.
Parallel evolution is the development of a similar trait in different not closely related species (that is in species of a different
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
), but descending from the same ancestor.
Parallel vs. convergent evolution
For a particular trait, proceeding in each of two lineages from a specified ancestor to a later descendant, parallel and
convergentConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
evolutionary trends can be strictly defined and clearly distinguished from one another.
When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not.
When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective. For instance, the striking example of similar placental and marsupial forms is described by
Richard DawkinsClinton Richard Dawkins, FRS, FRSL is a British ethologist, zoologist, Neo-Darwinian evolutionary biologist and theorist and a popular science author....
in
The Blind WatchmakerThe Blind Watchmaker is a 1986 book by Richard Dawkins in which he presents an explanation of, and argument for, the theory of evolution by means of natural selection. He also presents arguments to refute certain criticisms made on his previous book The Selfish Gene...
as a case of convergent evolution, because mammals on each continent had a long evolutionary history prior to the extinction of the dinosaurs under which to accumulate relevant differences.
Stephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum...
describes many of the same examples as parallel evolution starting from the common ancestor of all marsupials and placentals. Many evolved similarities can be described in concept as parallel evolution from a remote ancestor, with the exception of those where quite different structures are co-opted to a similar function. For example, consider
Mixotricha paradoxaMixotricha paradoxa is a species of protozoan that lives inside the termite species Mastotermes darwiniensis and has multiple bacterial symbionts. The name, given by the Australian biologist J.L. Sutherland, who first described Mixotricha in 1933, means “the paradoxical being with mixed-up...
, a microbe which has assembled a system of rows of apparent cilia and
basal bodies.A basal body is an organelle formed from a centriole, a short cylindrical array of microtubules. It is found at the base of a eukaryotic undulipodium and serves as a nucleation site for the growth of the axoneme microtubules...
closely resembling that of
ciliateThe ciliates are a group of protists characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...
s but which are actually smaller symbiont microorganisms, or the differently oriented tails of fish and whales. Conversely, any case in which lineages do not evolve together at the same time in the same ecospace might be described as convergent evolution at some point in time.
The definition of a trait is crucial in deciding whether a change is seen as divergent, or as parallel or convergent. In the image above, note that since
serineSerine is an organic compound with the formula HO
2CCHCH
2OH.-Occurrence:...
and
threonineThreonine is an α-amino acid with the chemical formula HO
2CCHCHCH
3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
possess similar structures with an alcohol side chain, the example marked
"divergent" would be termed
"parallel" if the amino acids were grouped by similarity instead of being considered individually. As another example, if genes in two species independently become restricted to the same region of the animals through regulation by a certain transcription factor, this may be described as a case of parallel evolution - but examination of the actual DNA sequence will probably show only divergent changes in individual basepair positions, since a new transcription factor binding site can be added in a wide range of places within the gene with similar effect.
A similar situation occurs considering the
homologyIn evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'. There are examples in different branches of biology...
of morphological structures. For example, many insects possess two pairs of flying wings. In beetles, the first pair of wings is hardened into wing covers with little role in flight, while in flies the second pair of wings is condensed into small
halteresHalteres are small knobbed structures found as a pair in some two-winged insects. They are flapped rapidly and function as accelerometers to help the insect maintain stability in flight, analogous to an aircraft's attitude indicator.The halteres evolved from wings...
used for balance. If the two pairs of wings are considered as interchangeable, homologous structures, this may be described as a parallel reduction in the number of wings, but otherwise the two changes are each divergent changes in one pair of wings.
Similar to convergent evolution, evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time (
dorsal finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
s of
sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s and
ichthyosaurIchthyosaurs were giant marine reptiles that resembled fish and dolphins...
s).
Examples
- Coloration that serves as a warning to predators and for mating displays have evolved in many different species.
- In the plant kingdom, the most familiar examples of parallel evolution are the forms of leaves
In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin. There is continued debate about whether the flatness of leaves evolved to expose the chloroplasts to more light or to increase the absorption of carbon dioxide. In...
, where very similar patterns have appeared again and again in separate genera and families.
- In butterflies
A butterfly is an insect of the order Lepidoptera. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage, and a spectacular metamorphosis into a familiar and colourful winged adult form. Most species are day-flying so...
, many close similarities are found in the patterns of wing colouration, both within and between families.
- Old and New world porcupine
Porcupines are rodents with a coat of sharp spines, or quills, that defend them from predators. They are endemic in both the Old World and the New World. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with an long tail....
s shared a common ancestor, both evolved strikingly similar quill structures; this is also an example of convergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
as similar structures evolved in both HedgehogA hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand. There are no hedgehogs native to Australia, and no living species native to North America;...
s and EchidnaEchidnas , also known as spiny anteaters, are four extant mammal species belonging to the Tachyglossidae family of the monotremes, an order of egg laying mammals. Together with the Platypus, they are the only surviving members of that order comprising the only extant mammals that lay eggs...
s.
- Contemporaneous evolution of the extinct browsing-horses
The evolution of the horse involves the gradual development of the modern horse from the fox-sized, forest-dwelling Hyracotherium. Paleozoologists have been able to piece together a more complete picture of the modern horse's evolutionary lineage than that of any other animal.The horse belongs to...
and extinct paleotheresPalaeotherium is an extinct genus of primitive perissodactyl ungulate. George Cuvier originally described them as being a kind of tapir, and as such, Palaeotherium is popularly reconstructed as a tapir-like animal...
both of which shared the same environmental space.
- Some extinct Archosaurs evolved an upright posture and likely were warm-blooded. These two characteristics are also found in most mammals. Interestingly, modern crocodiles have a four chambered heart and a crurotarsal
A crurotarsal ankle is one which can bend between the astragalus and calcaneum. Crocodilians and therian mammals have crurotarsal ankles, but these work in very different ways:...
, the later being also a characteristic of therian mammalsTheria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians .- Extent :...
.
- The extinct
In biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
pterosaurs and the birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s both evolved wings as well as a distinct beak, but not from a common ancestor.
- Internal fertilization
Internal fertilization is a form of fertilization of an egg by within the body of an animal, whether female or hermaphroditic. This is distinct from external fertilization, where the union of the ova and spermatozoa occur outside of the organism....
has evolved independently in sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s, some amphibians and amniotes.
- The Patagium
*In bats, the skin forming the surface of the wing. It is an extension of the skin of the abdomen that runs to the tip of each digit, uniting the forelimb with the body.*The patagium of a bat has four distinctions:...
is a fleshy membrane that is found in gliding mammals such as: flying lemurs, flying squirrels, sugar gliders and the extinct Volaticotherium. These mammals acquired the patagium independently.
- Pyrotheria
Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera Baguatherium, Carolozittelia, Colombitherium, Gryphodon, Propyrotherium, Proticia, and Pyrotherium....
ns have evolved a body plan similar to proboscideaProboscidea is an order containing one living family, Elephantidae, and several recently extinct families, Gomphotheriidae , possibly Stegodontidae and Mammutidae...
ns.
Parallel evolution between marsupials and placentals
One of the most spectacular examples of parallel evolution is provided by the two main branches of the
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s, the
placentalsEutheria are a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from non-eutherians by various features of the feet, ankles, jaws and teeth...
and
marsupialMarsupials are an infraclass of mammals, characterized by a distinctive pouch , in which females carry their young through early infancy.- History :...
s, which have followed independent evolutionary pathways following the break-up of land-masses such as Gondwanaland roughly 100 million years ago. In
South AmericaIn biogeography, the Neotropic or Neotropical zone is one of the world's eight terrestrial ecozones. This ecozone includes South and Central America, the Mexican lowlands, the Caribbean islands, and southern Florida, because these regions share a large number of plant and animal groups.It is...
, marsupials and placentals shared the ecosystem (prior to the
Great American InterchangeThe Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
); in
AustraliaAustralia is the smallest of the geographic continents, though not of geological continents. There is no universally accepted definition of the word "continent"; the lay definition is "One of the main continuous bodies of land on the earth's surface."...
, marsupials prevailed; and in the Old World the placentals won out. However, in all these localities mammals were small and filled only limited places in the ecosystem until the mass extinction of dinosaurs sixty-five million years later. At this time, mammals on all three landmasses began to take on a much wider variety of forms and roles. While some forms were unique to each environment, surprisingly similar animals have often emerged in two or three of the separated continents. Examples of these include the
litopternsThe Litopterna is an order of fossil hoofed mammals from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed....
and
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, whose legs are difficult to distinguish; the European sabre-tooth tiger
(SmilodonSmilodon , often called saber-toothed cat or saber-toothed tiger, is an extinct genus of the subfamily machairodontine saber-toothed cats endemic to North America and South America living from the Early Pleistocene through Lujanian stage of the Pleistocene epoch , existing for approximately 1.790...
) and the South American marsupial sabre-tooth
(ThylacosmilusThylacosmilus was a genus of sabre-toothed metatherian predators that first appeared during the Miocene. Remains of the animal have been found in parts of South America, primarily Argentina...
); the Tasmanian wolf and the European wolf; likewise marsupial and placental
molesThe two species of marsupial moles are rare and poorly understood burrowing mammals of the deserts of Western Australia.Marsupial moles spend most of their time underground, coming to the surface only occasionally, probably mostly after rains...
,
flying squirrelsThe Sugar Glider is a small marsupial originally native to eastern and northern mainland Australia, New Guinea, and the Bismarck Archipelago, and introduced to Tasmania.- Physical description :...
, and (arguably)
miceAntechinus is a genus of dasyurid marsupial that is indigenous to Australia and New Guinea. The majority of Antechinus species occur in Australia and only two species have been described in New Guinea...
.
External links
See also
- Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
- Evolutionary relay
- Homology (biology)
In evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'. There are examples in different branches of biology...
- Mimic
Biological mimicry occurs when a group of organisms, the mimics, have evolved to share common perceived characteristics with another group, the models, through the selective action of a signal-receiver or dupe. Collectively this is known as a mimicry complex. The model is usually another species...
ry