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Species are groups of organisms with similar physical, physiological, and behavioral traits that can mate and produce fertile offspring. When populations become isolated from each other and genetically distinct, they may lose the ability to interbreed. This process of creating new species from existing ones is called speciation. It's what gives Earth its incredible variety of life.

New are formed when two populations experience reproductive separation followed by genetic changes due to natural selection. Reproductive separation happens when individuals can't mate with others in their population because of changes in their alleles. For example, imagine a population of mice living in a large grassland area. If a development project divides the grassland into two, the mice populations become separated and genetically distinct. If the two areas have different environmental conditions, the mice populations will respond to those changes with genetic variations. Eventually, they will become so different that they can no longer interbreed successfully, and they will be considered different species.

Small populations and genetic drift

Smaller populations often experience genetic drift because they have less genetic diversity than larger populations. This means they have a smaller variety of alleles. As a result, new mutations can become fixed in the population more quickly than in larger populations, which can speed up the process of speciation.

Genetic drift is less likely to affect larger populations because any random variations in allele frequency will spread out across the whole population.

Genetic drift is when chance plays a role in which individuals survive, breed, and pass on their alleles. Alleles are different versions of the same gene.

What are the types of speciation?

In order for populations to split into two or more species, they must first become reproductively isolated. There are different ways this can happen. One way is through allopatric speciation, which occurs when populations become geographically separated. Another way is through sympatric speciation, which occurs when populations remain in the same area but become isolated through other means, such as isolation mechanisms. In parapatric speciation, a species is spread out over a large geographic area.

Allopatric speciation is the most common form of speciation. When populations become geographically separated, they may experience different environmental conditions and selection pressures that lead to genetic changes and reproductive isolation. Over time, the populations may become so genetically distinct that they can no longer interbreed.

In sympatric speciation, populations remain in the same area but become isolated from each other through other means. For example, a subset of a population may develop a new trait or behavior that prevents them from successfully mating with the rest of the population.

In parapatric speciation, a species is spread out over a large geographic area, and different subpopulations may experience different selection pressures. Over time, these subpopulations may become genetically distinct and reproductively isolated from each other.

Allopatric speciation

In allopatric speciation, populations become geographically separated and live in different places.

Allo- is derived from the Ancient Greek allos, meaning other, while -patric is derived from patris or fatherland.

Allopatric speciation
Allopatric speciation

Geographical separation can occur in several ways, such as through the appearance of a physical barrier that prevents two populations from intermingling. This can include bodies of water like oceans and streams, as well as landforms such as mountain ranges. Some barriers may over several millennia, while others, such as man-made dams and roads, can form relatively quickly.

The definition of a barrier depends on the size and mobility of the species in question. For example, a large river might be impossible to cross for small mammals and terrestrial insects, while it wouldn't be an obstacle for fish and reptiles. Plants cannot uproot themselves and move to a new location, while some birds can migrate for thousands of kilometers.

If the environmental conditions on either side of the physical barrier are different, then natural selection will influence the two populations in different ways over several generations. For instance, mountain ranges create different environments on both sides. Besides acting as a barrier for organisms, mountain ranges also act as a barrier to the flow of air. The leeward side of the mountain is sheltered from the wind, creating a dry, warm climate. In contrast, the windward side of the mountain will be cold and wet. Populations on opposite sides of the mountain would therefore be exposed to very different selection pressures and could very well become different species.

Sympatric speciation

In sympatric speciation, populations remain in the same place but become separated through mechanisms of isolation. A new species develops spontaneously.

Sym- is derived from the Greek syn meaning together. It is thought that sympatric speciation occurs due to different organisms occupying different environmental niches,  known as ecological separation. Ecological separation: populations are separated because they live in different environments within the same area. Niche: the area in which an organism resides (including abiotic and biotic factors) and the organism's role.

Sympatric speciation

Sympatric speciation is known to occur in bacteria due to their ability to exchange genes with other individuals through horizontal gene transfer. This process has been observed in species such as Bacillus and Synechococcus.

Horizontal gene transfer in bacteria refers to the exchange of genes between bacteria that are not offspring from binary fission. There are three mechanisms that enable horizontal gene transfer in bacteria - conjugation, transformation, and transduction. These mechanisms allow bacteria to acquire new genes that may provide an advantage in their environment, leading to the development of new species through sympatric speciation.

Parapatric speciation

Parapatric speciation occurs when two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes. This mode of speciation has three distinguishing characteristics: 1) mating occurs non-randomly, 2) gene flow occurs unequally, and 3) populations exist in either continuous or discontinuous geographic ranges. A species is spread out over a large geographic area and individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population's range [^3]. This is due to the fact that the species are separated by the differences within the same environment, which occurs by an extreme change in the habitat.

Parapatric speciation

Parapatric speciation can occur when an environment is polluted. For example, mining activities can leave large amounts of metals in the soil such as lead zinc can prevent most plants from growing. However, some grasses, such as buffalo grass, can tolerate the metals and continue to grow in these polluted areas. This can lead to the formation of a new species, as the buffalo grass seeds pass on their characteristics to their offspring, which can be adapted to the polluted environment. This process is known as parapatric speciation, which is a type of speciation in which there is free exchange of genes between two populations of organisms living in directly adjacent but environmentally different habitats.

Example mechanisms of isolation

Isolating mechanisms are the characteristics that prevent different species from interbreeding successfully. Populations can inhabit different niches within the same area, making it so that members of different populations rarely interact. For example, insects usually lay eggs within the type of fruit in which they were born, leading to less gene flow between different fruits and making them reproductively isolated. Populations can also become separated through time when a mutation arises that causes some members of the population to start breeding earlier or later in the year, leading to different breeding seasons that do not overlap.

In many species, mating is preceded by courtship, with same-species recognition being a crucial part of this process. Mutations that cause noticeable changes in the appearance or behavior of an individual, such as changes in the color of their feathers or the sounds of the mating call, can prevent others from recognizing them as potential mates and thus avoid reproducing with them.

While humans are still evolving, just like every other organism on Earth, the likelihood of human populations undergoing speciation is low due to the high level of globalisation and technology [^4]. However, it is possible that if different human populations become geographically separated and did not intermingle, and their habitats possess different selection pressures, they might accumulate enough genetic differences over many generations to eventually become different species.

Speciation - Key takeaways

You are exactly right! Speciation is the process by which new species arise from existing ones, and this occurs when populations of organisms become genetically and reproductively distinct from their ancestors.

There are several different modes of speciation, including allopatric, sympatric, and parapatric speciation. In allopatric speciation, populations become geographically separated and live in different places, which can lead to genetic divergence and reproductive isolation. In sympatric speciation, populations remain in the


What causes speciation in biology? 

In order to split into two or more species, populations must first become reproductively isolated.The two populations must then accumulate enough genetic differences that they can no longer interbreed with one another. These genetic changes are caused by varying selection pressures for the two populations. At this point, they are considered different species. 

Can speciation occur in humans? 

Humans, like all other organisms on Earth, are still evolving. Theoretically, if several human groups became geographically separated and did not intermingle at all, and their respective habitats had different enough selection pressures, they might accumulate enough genetic differences over a very long time that they could not interbreed anymore. However, given our present level of globalisation, this is highly unlikely!  

What is sympatric speciation? 

Sympatric speciation occurs when two groups of a population remain in one place but undergo a mechanism of isolation. This is in contrast to allopatric speciation, where the population is separated geographically into two or more groups. 

How are new species formed? 

Speciation occurs when two populations undergo reproductive separation first, followed by genetic changes within each new population due to natural selection. 

What is allopatric speciation? 

Speciation that occurs when populations become geographically separated from one another and live in different regions.

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