Introduction to Biology Pt. 2: The Biological Species Concept

Introduction to Biology Pt. 2: The Biological Species Concept

When studying the life sciences, there are a lot of in-depth concepts to take in. Depending on the the type of science you are studying, biology vs. evolution, for example, you may even have to learn a handful of mathematical formulas to fully appreciate the material. Here, we are just having a light-hearted overview of the life sciences, so a light serving of sativa will do just fine.

In my experience, sativa helps me to not get lost in wordy texts (reading that is not broken up by graphics/tables or formulas) and keep my mind sharp and able to take in all relevant information. Grinding about 60mg (less than 1/4 of a 1g bud) of sativa and smoking just a small pinch of that for over a 3-5hr period is perfect for maintaining a healthy attention span for learning.

Black Flower Science Co. does not claim to be a medical professional and does not offer recommendations as a substitute for medical advice. All advice and recommendations are based on personal experience of the benefits of medical marijuana. If you are experiencing severe or declining mental health symptoms, please seek the advice of a medical professional.

On the surface, it is easy to distinguish a species from another. For example, it is obvious that cats and birds are different. Perhaps you are using appearance to determine this, but that is not always enough to define a species.

The biological species concept attempts to solve this challenge in identification, by defining species as members within a population that interbreed with each other and produce viable offspring. 

Here, we’ll explore the way a species is defined through the biological species concept in greater detail. We’ll also dive into how distinct species are formed.  

What maintains the distinction between species?

During the reproduction of multicellular organisms, a zygote is formed whenever two gametes fuse together. In some animals, the successful fertilization of an egg by a sperm results in a zygote. Prezygotic and postzygotic reproductive barriers encourage reproductive isolation, because they prevent the formation of a new species.

Prezygotic barriers 

Prezygotic barriers prevent the formation of a zygote, often by not allowing intercourse to take place at all. A polar bear from the arctic and a black bear from the Rockies will never mate with each other, because their environments are very different. This is thanks to habitat isolation where two different species may never interact because they live in different areas. 

In temporal isolation, the reproductive clocks of opposite species do not align. For example, animals that hibernate during the winter and those that aestivate during the summer will mate during opposite times of the year. Behavioral isolation is differences in courtship resulting in opposite species not finding each other attractive. 

If the previously mentioned mechanisms don’t prevent intercourse, mechanical or gametic isolation may occur. Mechanical isolation prevents their reproductive structures from meshing well together, and gametic isolation is when the sperm is unable to fertilize the egg.

Photo by Boston Public Library on Unsplash

Postzygotic barriers

In the event that prezygotic barriers are overcome and a zygote is formed, chromosomal differences will hinder its development into a healthy and fertile adult. For example, the offspring between a horse and a donkey can survive into adulthood, but they are sterile because its parents have different chromosome numbers.

How are new species formed?

The biological species concept considers speciation as the phenomenon by which a species diverges to form reproductively isolated groups. This concept foreshadows evolution, since as a collective there is a common gene pool amongst the interbreeding members of a species. Because the genes are not exchanged to different species, gene flow is restricted, distinguishing a single species from others. There are four major kinds of speciation- allopatric, peripatric, parapatric, and sympatric. 

Types of speciation

Allopatric speciation states that geography is the cause of separation between a population from its parent species. Charles Darwin, the father of evolution, observed this when studying the finches of the Galapagos Islands. He discovered that the numerous kinds of finches became distinct species, because the ocean and different resources in their respective islands separated them from each other. 

Peripatric Speciation is similar to allopatric speciation, but the difference is that a small population from the edge of a larger population is separated. 

In parapatric speciation, species are not separated by geographical barriers such as in allopatric and peripatric speciation. Instead, they are separated by differences within the same environment

Lastly, sympatric speciation is a population’s evolution into its distinct species that takes place within the same location as its parent species. Some scientists debate over whether this is actually possible, because barriers to prevent individuals of a species are not present making this phenomenon seem spontaneous.

Chart Of Cannabinoids Print – 18×24

Is the biological species concept enough?

The biological species concept is highly debated and does not satisfy the discoveries of all naturalists. Some of its limitations include not being able to be applied to asexually reproducing organisms and hybrids of different taxa. It is also difficult to use when the only remnants of a species can be traced through fossils, since gene flow and reproduction cannot be followed. For these reasons and more, other species concepts have been introduced in order to develop a more universally accepted way to define species. 


Bush, G. L. (1975). Modes of animal speciation. Annual Review of Ecology and Systematics, 6(1), 339-364. 

Rutledge, K., Ramroop, T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., … Hunt, J. (2012, October 9). Speciation.

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