Convergent Evolution represents a phenomenon when two distinct species with differing ancestries evolve to display similar physical features. Environmental circumstances that require similar developmental or structural alterations for the purposes of adaptation can lead to convergent evolution even though the species differ in descent. These adaptation similarities that arise as a result of the same selective pressures can be misleading to scientists studying the natural evolution of a species. 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 construction, due to the physical constraints imposed upon wing shape. Similarity can also be explained by shared ancestry, as evolution can only work with what is already there—thus wings were modified from limbs, as evidenced by their bone structure

Convergent Evolution is a common theme in the evolution of animals. It always occurs when two unrelated species independently evolve similar traits to cope with specific evolutionary challenges, like living in ice-cold water or eating ants. Sometimes convergent evolution is so powerful that creatures that began as entirely different animals start to look almost the same, as is the case with the skulls of the extinct living Grey Wolf (largest wild canid, with height ranging from 0.6 to 0.95 m (26-38 in) and weight from 20 to 65 kg (44-150 lb)).

What are the Traits occurring through Convergent Evolution?

Traits arising through convergent evolution are termed analogous structures, in contrast to homologous (the basis of organization for comparative biology) structures, which have a common origin. An analogy is a trait or an organ that appears similar in two unrelated organisms. Bat and pterosaur (flying reptiles) wings are an example of analogous structures, while the bat wing is homologous to human and other mammal forearms, sharing an ancestral state despite serving different functions. Similarity in species of different ancestry that is the result of convergent evolution is called “Homoplasy”.
 

What is Divergent Evolution?

The opposite of convergent evolution is divergent evolution, whereby related species evolve different traits. On a molecular level, this can happen due to random mutation unrelated to adaptive changes. Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics through genetic drift and natural selection.
 

What is Parallel Evolution?

Convergent evolution is similar to, but discernible from, the phenomena of evolutionary relay and parallel evolution. Evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems at different times—for example the dorsal fins (a fin located on the backs of various unrelated marine and freshwater vertebrates) of extinct ichthyosaurs and sharks. Parallel evolution occurs when two independent species evolve together at the same time in the same eco-space and acquire similar characteristics—for instance extinct browsing-horses (ancestry of the modern horse).
 

What are the causes of Convergent Evolution?

If organisms occupy similar ecological niches (a term describing the relational position of a species or population in its ecosystem to each other) —that is, a distinctive way of life, then similarity can occur. A typical comparison is between the ‘marsupial fauna’ of Australia and the ‘placental mammals’ of the Old World. The two lineages are clades—that is, they each share a common ancestor that belongs to their own group, and are more closely related to one another than to any other clade—but very similar forms evolved in each isolated population. Many body plans, for instance sabre-toothed cats and flying squirrels, evolved independently in both populations.
 

What are some examples of Convergent Evolution?

There are hundreds or even thousands of examples of convergent evolution in nature. The camera eye of cephalopods (e.g., squid), vertebrates (e.g., mammals) and cnidarians (e.g., box jellies) are some of the most eminent examples of convergent evolution. Their last common ancestor had at most a very simple photoreceptive spot, but a range of processes led to the progressive modification of this structure to the advanced camera eye - with one delicate difference: The cephalopod eye is "wired" in the opposite direction, with blood and nerve vessels entering from the back of the retina, rather than the front as in vertebrates. The similarity of the structures in other respects, despite the complex nature of the organ, exemplifies how there are some biological challenges (vision) that have an optimal solution. Convergent evolution took place between the Giant Armadillo of North America, the Giant Anteater of South America, the Giant Pangolin of Africa, and the Spiny Anteater (echidna) of Oceania. These animals all have an analogous body shape, including a long proboscis, due to their adaptations to consuming ants, while their present common ancestor is over 155 million years old and looks nothing like them.

Will a trait re-evolve in a Convergent manner?

In certain cases, it is difficult to tell whether a trait has been lost then re-evolved in a convergent manner or whether a gene has simply been 'switched off' and then re-enabled later. From a mathematical point of view, an unused gene has a reasonable probability of remaining in the genome in a functional state for around six million years, but after ten million years it is almost certain that the gene will no longer function.
 

How to compare Parallel and Convergent Evolution?

For a specific trait, proceeding in each of two lineages from a specified ancestor to a later descendant, the parallel and convergent evolutionary trends can be strictly defined and clearly distinguished from one another.

• When both descendants are identical 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 Dawkins, a British biologist, in The Blind Watchmaker(book by Richard Dawkins) 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 Gould, an American biologist, 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 paradoxa’, a microbe that has assembled a system of rows of apparent cilia (an organelle, a specialized part of a cell) and basal bodies (an organelle) closely resembling that of ciliates (a group of protozoans) but that are actually smaller symbiont micro-organisms, or the differently oriented tails of fish and whales. Symbiosis is close and often long-term interactions between different biological species.
• In general, any case in which lineages do not evolve together at the same time in the same eco-space might be described as convergent evolution at some point in time.

What is the significance of Convergent Evolution?

The extent to which convergence impacts the products of evolution is the topic of a popular disagreement. In his book Wonderful Life, Stephen Jay Gould argues that, if the tape of life were reversed and played back, life would have taken a very different course. Simon Conway Morris counters this argument, arguing that convergence is a prevailing force in evolution, and due to the fact that the same environmental and physical constraints act on all life, there is an "optimum" body plan that life will inevitably evolve toward, with evolution bound to stumble upon intelligence - a trait of crows, and dolphins - at some point. Convergence is difficult to quantify, so progress on this issue may require exploitation of engineering specifications (e.g., of wing aerodynamics) and comparably rigorous measures of "very different course" in terms of phylogenetic (molecular) distances.