Why Does Convergent Evolution Occur?
Convergent evolution usually occurs when two or more unrelated species are bound to remain in a similar environment, and so they are forced to respond to many similar selection pressures and adapt themselves gradually. It can also occur when many unrelated species are isolated in similar niches but in different environments.
Convergent evolution is a type of evolution that occurs when species have different ancestral origins but have developed similar features. Meaning that the descendent species that show similar adapting features have different ancestral species.
It occurs when two different species from unrelated lineage develop the same traits or features. This happens because they live in similar habitats, and have to develop solutions to the same kind of problems.
In Convergent evolution, natural selection may mold different body structures of the different species in ways that perform similar functions but the body structures may look different.
In this type of evolution, the descendants resemble each other more than their ancestors did with respect to some features.
Meaning that the ancestral species groups were a lot different from each other, but they have evolved descendants species groups that perform similar functions and have similar anatomy.
Example of convergent evolution: Eyes of Octopus and those of Mammals, Winges of butterfly and birds, etc.
The organs having different origin but performing same functions are called analogous organs and the phenomenon is called analogy. Analogy is the result of Convergent evolution.
In divergent evolution, related species evolve different traits and functions. And in convergent evolution, unrelated species evolve similar traits and functions.
Convergent Evolution occurs due to the following broad reasons:
1. When different species live in similar habitats
The process of gradual evolution demands that an organism tries to better adapt in its own environment in order to better survive and reproduce if it gets isolated from other environments. If the organisms get well-adapted it will survive and if not it will soon die and become extinct.
This concept stays true and well-agreed in convergent evolution. As it is seen that, different organisms independently evolve similar traits in their type of environment while their ancestors didn’t show any type of similar traits.
For example, sharks and dolphins look relatively similar despite being entirely unrelated. Sharks are egg-laying fish that catch their prey by smelling blood and stay in the water, while dolphins are curious mammals that navigate and catch their prey by making clicking sounds and listening to their echoes.
Both dolphins and sharks swim after their prey in the ocean. We know that dolphins and sharks are not closely related, and they didn’t inherit their similar body shapes from a common ancestor. Their streamlined bodies, dorsal fins, and flippers are the result of convergent evolution.
Here, it can be said that from one ancient common ancestor, one lineage stayed on land and had evolved into mammals that include the wolf-like extinct Pakicetus, and another linage that returned to the water had gradually evolved into modern-day dolphins.
Another ancestor that was already been living in the ocean water stayed there and gradually over time had undergone many tweaks to become the modern-day shark.
Yet despite their different ancestors, both animals (dolphins & sharks) ended up in their similar evolutionary niches and aquatic environment and so due to convergent evolution, they became streamlined swimmers with smooth skin and streamlined fins.
2. The evolution of similar or identical mutations in independent lineages
Convergent evolution can also occur due to the parallel evolutionary changes. Let’s understand why?
Parallel evolution which is actually the evolution of similar or identical mutations in independent lineages due to the environment’s selection effect, can over time also lead to convergent evolution.
Parallel evolution that occurs under similar environmental conditions in distantly-related organisms results in plants and animals that are morphologically very similar in overall appearance, is called convergent evolution.
It should be noted here that some authors use these two terms interchangeably.
When many different species show similar genetic changes (that’s parallel evolutionary changes) that can be due to similar or identical mutations, causing the organism to better adapt to the environment. This causes convergent evolution over time.
Actually convergent evolution and parallel evolution are two different concepts of evolution. Convergent evolution shows different ancestors, while Parallel evolution shows similar ancestors.
Convergent evolution occurs when descendants resemble each other more than their ancestors did with respect to some features.
On the other hand, parallel evolution implies that two or more lineages have changed in similar ways so that the evolved descendants are as similar to each other as their ancestors were.
So, multiple factors can contribute to parallel evolution. And when each lineage of parallelly evolving organisms try to better adapt to the environment, mutations in some genetic targets minimize pleiotropic effects during adaptation.
This can lead to dissimilarities from the ancestors of the same lineage leading to convergent evolution.
3. The evolution in independent lineages of alleles that are shared among populations
Another genetic reason for convergent evolution is collateral genetic evolution. Let’s understand why?
Collateral evolution is caused due to the genetic changes that are inherited from an ancestral population or from hybridization between species.
In this type of evolution, independent lineages of alleles are shared among populations. It is likely to be common in species in which a single large population is surrounded by multiple geographical isolates and so they are often bound to reproduce amongst themselves.
Collateral evolution by hybridization has been documented only recently and is likely to be widespread in nature.
Collateral evolution along with parallel evolution has been found in many taxa mostly in the geographically isolated regions where negligible gene flow occurs.
An emerging hypothesis is that both collateral and parallel evolution results from the fact that mutations in some genetic targets minimize pleiotropic effects while simultaneously maximizing adaptations.
Such a cause can lead to convergent evolution and this hypothesis is still not yet proven with strong evidences.
What kind of features can convergent evolution lead to?
Convergent evolution can lead to many similar evolving traits amongst different species as a result of adaption to a similar environment or ecological niche.
Convergent evolution can lead to similar traits, similar functions, similar types of genetic mutations, similar adaptations to the environment, similar physiological actions, and different anatomical structures of the body organs amongst the different variety of species Inhabitating a similar environment and similar niche.
Those different species that have been evolved by convergent evolution will show similar functions in the same environment but their body anatomy will differ.
This simply means that the organs of the different species that have evolved by convergent evolution will show different origin (ancestry) but will strictly perform the same function in their environment because they were adapted to do so.
Convergent evolution will create strong Analogous structures that have similar form or function but were not present in the last common ancestor of those groups.
Just like in the case of flying insects (arthropods), birds (aves), bats (mammals) you will find that all of these can fly. It’s because all of these have developed and have adapted similar functions to fly. But, they don’t have any common ancestor thus their body anatomy won’t match so well with each other.
Some examples of convergent evolution
All the examples in each point mentioned below are strong evidences of convergent evolution.
Each point has examples that show the same function and are similar in structure but evolved independently.
- Eyes of Octopus and those of mammals do similar functions.
- Wings of buttery and those of birds help them fly.
- Flippers of whales and those of Penguins helps them swim.
- Similar functions of the tubers of sweet potato (modified root) and those of potato (modified stem).
- Similar nature of the flight/wings of insects, birds, pterosaurs, and bats.
- Sharks (cartilaginous fishes) and dolphins (aquatic mammals) look relatively similar despite being entirely unrelated.
- The marsupial mole has many resemblances to the placental mole.
- The marsupial thylacine (Tasmanian tiger or Tasmanian wolf) had many resemblances to placental canids.
- A number of mammals have developed powerful fore-claws and long, sticky tongues that allow them to open the homes of social insects like ants and termites and consume them.
- Marsupial koalas of Australia have evolved fingerprints, indistinguishable from those of non-related primates, such as humans.
Do you know that Convergent Evolution is a pattern of macroevolution?
Microevolution is simply a change in gene/allele frequency within a population. And when many such microevolutions occur over a longer period of time (maybe between thousand to millions of years) then macroevolution occurs.
It is to be noted that the two important patterns of macroevolution are adaptive radiation and convergent evolution.
Adaptive Radiation is a divergent evolution that shows that a single species has diversified over a longer time period into a clade containing many species.
Convergent evolution occurs when species have different ancestral origins but have developed similar features.
The word converge means “to come together”. This pattern of macroevolution happens when distinctly different species become more similar in structure and function.
Usually, this type of macroevolution is seen in different species that live in similar environments. The species are still different from one another, but they often fill the same niche in their local area.
A pattern means the repetition of something. And so, macroevolution can have both the patterns of adaptive radiation (a type of divergent evolution) or convergent evolution taking successively one after the other during the evolution process of any species.
It is also to be noted that the occurrence of more than one adaptive radiation in an isolated geographical area with different habitats leads to convergent evolution as well. So, the patterns of convergent evolutions can be more often seen during the macroevolutionary studies of any species.
