 So, what is a species, really? Do you know your species? Do you know what our species is? So everybody knows that we are humans and therefore we belong to the species called Homo sapiens. But how sure are you that you really do belong to Homo sapiens? If you look at, say, another ape like the chimpanzee, you know that that chimpanzee is a different species. But how sure are you that we are different species? We can look at our physical attributes. We are distinctly different. So, is that enough to say that we are different species? Some biologists would look at our chromosome number. How many chromosomes do you have inside a cell? Well, if you look at our cells, we have 46 chromosomes whereas chimpanzees have 48. Is that enough to say that we are distinct from them? Even amongst ourselves, we would like to think we all belong to the same species. But how sure are you that we are from the same species? Now, there are various ways by which we distinguish one species from another. But in biology, we have one major criterion that we make use to distinguish species. And that is the presence of the reproductive barrier. So, what is a reproductive barrier? Basically, species are distinct from one another if they are unable to have sex or produce offspring or produce viable offspring or if that offspring can survive, that offspring can produce other offspring. So, that is a major consideration to distinguish one species from another. So, for example, if you have a chimpanzee having sex with heaven forbid a human, you know that they will not be able to produce organisms. Now, this becomes problematic though when we look at other organisms say, extinct species. How can we say that homo erectus is distinct from homo sapiens? We cannot obviously make homo erectus with homo sapiens because homo erectus is already extinct. We only have their bones. And what about bacteria or other imperfect fungi? We don't know yet how these organisms have sex. So, how are we to determine one species from another? So, one alternative consideration to distinguish species is to look at the evolutionary concept of what a species is. Basically, if you share a common ancestor that is fairly recent enough, then you probably belong to the same species in the same way that a brother and a sister within a family share parents. So, they must be closely related in the same way that cousins are related because they share grandparents. So, if we all belong to the same species, we must be able to identify a single common ancestor. But the question is how far back should we go? Is 1,000 generations enough? 10,000 generations? 1 million generations? So, basically, if you're going to consider all these together, the species concept is a bit fluid. We don't really know what a species is. We don't really know if we are distinct from one another based on our species designation. So, what is a species really? Basically, a species is just a human concept within a point of time. If we are going to consider, for example, a single individual giving rise to many individuals through time, then what you have is just a continuum. It can be likened to, say, several branches on a tree or, for example, a river with several subbranches. So, when they branch out eventually and then you cut across these points, for example, you have a branch here, a branch in a branch here, and then you cut that, you will have points. And these points will represent species at that particular time. And then if you move on at another time, then you will have other points, distinct from these previous points. So, a species concept really does not exist. There's no such thing as a species because a species is just a point in time. But as humans, it is our nature to put order in chaos. So, we don't want to look at things without fully understanding what they are. And one way to understand these things or these events or these phenomena is to give them names. That's why we give them scientific names. So, for the purpose of discussion, you just have to put classification to these organisms and we give them species names. Now, we may classify them based on their morphology, physiology, or where they are found, but one emerging discipline in taxonomy is the use of DNA bar codes. Now, you may ask, what are DNA bar codes? Remember that each individual has a cell and within each cell, or several cells, and within each cell, you have your DNA found in your chromosomes. Now, these DNA contain series of nucleotides and a sequence of nucleotides can specify genes. So, DNA bar codes can also work in the same way as those found in markets. I'm sure all of you have been to a supermarket where you go to the cash register and then you have a laser gun and then they will just shoot at the item using the bar codes and then the bar codes will indicate in the cash register what the item is, how much it costs, what is its make, et cetera, et cetera. So, the DNA bar code can work in the same way. How? If you look at your DNA, extract the DNA, focus on a specific gene, sequence that gene and then cross reference that with a database and if you get that sequence, compare that with a database, you can basically identify an individual, an unknown individual to a known species. For example, in animals, we can amplify the cytochrome C oxidase subunit 1 gene. If we amplify that gene across many taxa, many known taxa, then we can build up a database and that database can be used as a cross reference data for any unknown individual. For example, if you go to a restaurant or at a supermarket or to a wet market and then you bought lapulapu because that's what the fishmonger said, it's lapulapu, then you'd probably believe that person. But how sure are you that it is lapulapu when in fact it could be the lagang bukid which is much cheaper compared to lapulapu but they taste the same, especially if the fish has already been processed, say it's already in a filet form. One way to identify that is to extract a tissue, then extract the DNA from that tissue and sequence of cytochrome C oxidase subunit 1 gene. And then once you have those sequences or that particular sequence, you can cross reference that to a database. And in this database, if it tells you, say that it is 99.9% or 100% identical to lapulapu, then you can certainly say that, oh okay, this is lapulapu. So DNA barcode works at that way and you can apply this to as many organisms as possible because practically all living things have DNA. It's just a matter of building up a database. Now, in the Institute of Biology, UPD-LIMAN, we have a DNA barcoding laboratory where we try to build up the Philippine database for endemic species for both plants and animals. So what we do is we go to the different parts of the Philippines. We collect endemic species. We extract the DNA from these species. And then we sequence them and store them in the DNA database. For example, GenBank or Bode or the barcode of life data systems. Now, as molecular biologist, we cannot claim that we can identify every endemic species in the Philippines. That's why we have to work with taxonomists who can help us identify these species. So the taxonomists and the DNA barcoder works hand-in-hand with the taxonomists identifying the species based on their physical attributes and then the DNA barcoder extracting the DNA from these identified species and then submitting these sequences to the database which also include all the other morphological data and collection data provided by the taxonomist. And then these data will be submitted to the database and that will be the reference sequence for that species. Now ideally, we should have as many sequences as possible from as many individuals for every species because we expect that within even the same species we have genetic differences. For example, I may be different from the next individual in five nucleotides in the DNA for the CO1 and that is to be expected because we are all different. We differ from one another because of the mutations that have taken place across our DNA. Now how do we know if a species belong or if an unknown individual belongs to a particular species if the match is not 100%. For example, if I obtain my DNA and then I sequence the CO1 and it says 99.5% homo sapiens. Does that mean I am homo sapiens or does that mean I am not homo sapiens? So this is where the threshold values come in. You have to establish a threshold value for every gene, for every taxonomic group because for some species a 3% difference means that they belong to the same species. Any value larger than that means that they belong to different species. In birds for instance they use a threshold value of 3% or less. If there is a difference of 3% or less between an unknown individual and a reference sequence then that would mean they belong to the same species. If it exceeds that threshold value then it means that they belong to different species. But this threshold value differs from different organisms. It may be different for birds, for fishes, for insects or even humans. So it is important therefore that we build up the database from as many individuals as possible from as many species as possible so that we can compare and establish the threshold values if we can. Because the difference here lies when the intraspecific variation and the intraspecific variation do not overlap. Now what do you mean by intraspecific variation? Intraspecific variation simply means the genetic differences that you find within the same species. Intraspecific variation on the other hand means the genetic differences between species. Now logic dictates that the closer individuals are with one another then they should be more similar to one another with respect to their DNA. The more distant they are with respect to one another then the more different their DNA sequences should be. So between intraspecific variation and intraspecific variation you would expect that the intraspecific variation range would be lower compared to the intraspecific variation range and you should not expect therefore the two to overlap. If there is no overlap then you can establish the threshold value. Now the problem lies when these two ranges overlap. If they overlap then you cannot establish a threshold value and therefore the DNA bar codes may not be that useful. Which brings us then back to our original question what is a species really? Do we then identify species based on their similarity with their sequences? Do identify species therefore based on our DNA? Now Richard Dawkins proposed way back the concept of the selfish gene. So what does that mean? We have this illusion that we are the ones in charge when in fact it is the genes themselves that try to get passed on from generation to generation. They just use us to make sure that they themselves are passed on because if that person that carries those genes cannot reproduce and never cannot produce offspring that means the end of the genes. So basically the purpose of the gene is to ensure that they get passed on. So which one is the species then? Which one is the sentient entity? Which one is the living organism? So now we don't know for sure what a species is. So do we still identify them based on our DNA? Well want things for sure biologists will have to find that out.