Science (Part 1)
Tuesday 25th April, 2006 00:17 Comments: 0
According to Wikipedia: "A species is a group of organisms that can interbreed in nature to produce a fertile offspring" - or at least that's the idealistic definition.
Seeing as a mule is infertile, it's therefore possible to argue that horses and donkeys are not the same species (which is how I see it, although I believe they are the same genus). However, there have been more than 60 documented cases of foals born to female mules since 1527, so you could perhaps argue they are the same species. This is presumably why people normally refer to the mule or hinny as a hybrid species, but even the term hybrid is complicated (the term is also related to interbreeding).
Although the current scientific understanding of species suggests that there is no rigorous and comprehensive way to distinguish between different species in all cases, biologists continue to seek concrete ways to operationalize the idea. One of the most popular biological definitions of species is in terms of reproductive isolation; if two creatures cannot reproduce to produce fertile offspring, then they are in different species.
In biology, hybrid has three meanings. The first meaning is of crosses between two animals of different taxa. Hybrids between different species within the same genus are sometimes known as interspecific hybrids or crosses. Hybrids between different sub-species within a species are known as intra-specific hybrids. Hybrids between different genera are sometimes known as intergeneric hybrids. The second meaning of "hybrid" is crosses between populations, breeds or cultivars of a single species. This second meaning is often used in plant and animal breeding. The third meaning is in molecular biology.
Interspecific hybrids are bred by mating two species, normally from within the same genus. The offspring display traits and characteristics of both parents. The offspring of an interspecific cross may be sterile. Sterility is often attributed to the different number of chromosomes the two species have, for example donkeys have 62 chromosomes, while horses have 64, mules and hinnies have 63. Mules, hinnies, and other normally sterile interspecific hybrid normally cannot produce viable gametes because the extra chromosome cannot make a homologous pair at meiosis, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in both female mules and hinnies has been reported with a donkey as the father.
The rise of a new species from a parental line is called speciation. There is no clear line demarcating the ancestral species from the descendant species. Interbreeding is no longer able to take place after speciation occurs. The separated group will be (after many generations) a new species and therefore will not be able to breed with the old species that it used to be.
Which brings me back to the point of this entry. It looks like an animal can give birth to a different species (although given the strange historical classifications and multiple definitions of the term itself, this statement can\'t be entirely trustworthy), but it appears that it only gives birth to a hybrid species rather than a new one. However, it is thought that this is how the Lonicera fly came about, and possibly the Pomarine Skua, presumably thanks to speciation (that happens after many generations). Perhaps if there is sufficient evidence, it\'d be possible to prove the theory of evolution, as right now the evidence seems to point towards adaptation. But maybe that's because we haven\'t been studying things for long enough.
Seeing as a mule is infertile, it's therefore possible to argue that horses and donkeys are not the same species (which is how I see it, although I believe they are the same genus). However, there have been more than 60 documented cases of foals born to female mules since 1527, so you could perhaps argue they are the same species. This is presumably why people normally refer to the mule or hinny as a hybrid species, but even the term hybrid is complicated (the term is also related to interbreeding).
Although the current scientific understanding of species suggests that there is no rigorous and comprehensive way to distinguish between different species in all cases, biologists continue to seek concrete ways to operationalize the idea. One of the most popular biological definitions of species is in terms of reproductive isolation; if two creatures cannot reproduce to produce fertile offspring, then they are in different species.
In biology, hybrid has three meanings. The first meaning is of crosses between two animals of different taxa. Hybrids between different species within the same genus are sometimes known as interspecific hybrids or crosses. Hybrids between different sub-species within a species are known as intra-specific hybrids. Hybrids between different genera are sometimes known as intergeneric hybrids. The second meaning of "hybrid" is crosses between populations, breeds or cultivars of a single species. This second meaning is often used in plant and animal breeding. The third meaning is in molecular biology.
Interspecific hybrids are bred by mating two species, normally from within the same genus. The offspring display traits and characteristics of both parents. The offspring of an interspecific cross may be sterile. Sterility is often attributed to the different number of chromosomes the two species have, for example donkeys have 62 chromosomes, while horses have 64, mules and hinnies have 63. Mules, hinnies, and other normally sterile interspecific hybrid normally cannot produce viable gametes because the extra chromosome cannot make a homologous pair at meiosis, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in both female mules and hinnies has been reported with a donkey as the father.
The rise of a new species from a parental line is called speciation. There is no clear line demarcating the ancestral species from the descendant species. Interbreeding is no longer able to take place after speciation occurs. The separated group will be (after many generations) a new species and therefore will not be able to breed with the old species that it used to be.
Which brings me back to the point of this entry. It looks like an animal can give birth to a different species (although given the strange historical classifications and multiple definitions of the term itself, this statement can\'t be entirely trustworthy), but it appears that it only gives birth to a hybrid species rather than a new one. However, it is thought that this is how the Lonicera fly came about, and possibly the Pomarine Skua, presumably thanks to speciation (that happens after many generations). Perhaps if there is sufficient evidence, it\'d be possible to prove the theory of evolution, as right now the evidence seems to point towards adaptation. But maybe that's because we haven\'t been studying things for long enough.