On The Origin Of Species

On the Origin of Species chapter IV outlines Darwin’s proposal on how a new species is generated via natural selection over a long period of time. In Darwin’s theory of speciation, he proposes that all organisms within a species must express some degree of variation, which allow for organisms with the most advantageous variations to produce the most offspring (Darwin 10) This also means that the variations must be heritable from one generation to the next. In chapter IV Darwin uses the examples variants causing a wolf to be slimmer so it can run faster to escape predators and hunt down prey, and a bear may have a variant that allows it to prey on more abundant sources of food (Quote: “Let us take the case of a wolf, which preys on various
If, however, an isolated area be very small, either from being surrounded by barriers, or from having very peculiar physical conditions, the total number of the inhabitants will be small; and this will retard the production of new species through natural selection, by decreasing the chances of favourable variations arising” Darwin 11). If new organisms were introduced it could, and often does, interfere with the interaction between a species variant and the environment. The isolation will ensure that an advantageous variant will win out over a disadvantageous one. As time goes on, the advantageous variant will become established in the population, making it appear as if the species is perfectly adapted for their environmental niche. At the end of chapter, Darwin notes that as advantageous variants are selected over disadvantageous one, it will lead to divergence from the parent species. When these diverged species start to diverge themselves, it creates a cascade and ultimately limits the ability for the population to grow further. Thus, those that diverged but lack a favorable variant will die. As more and more divergences come about the subspecies may develop into an entirely different species over tens of thousands of years. To sum it up, in Darwin’s theory of speciation involves: variation amongst individuals in a species that must be inheritable,
Today, we have numerous speciation concepts: ~25 that are all equally efficient in their own right. This lack of set definition, also adds further contention to the lumpers vs. splitters debate which additionally fuels misconceptions in society and can have major impacts on conservation efforts. One idea idea that Darwin had that compared completely to the modern speciation idea is the theory of speciation by sexual selection, in that the males that are able to mate more frequently by being more attractive to females via some sort of ornament, song, etc. and can pass that variant on to their offspring are more fit and can cause divergence to start to take place. For the most part, scientists would agree that like Darwin’s theory there must be a barrier to gene flow. In Darwins time, the term gene flow didn’t exist, but he described the definition in On the Origin of Species. What is different about this and the modern view is that instead of a geographic barrier situation (allopatry), there’s several other different types like reproductive barriers: both pre- and post-zygote, parapatric speciation, peripatric, and sympatric. The last three are reproductive barriers in their own right after the diverged species and the parent species re-meet. So, while Darwin got the geographic barrier part right, he missed another part: barriers can occur by different mechanism. Another major idea by Darwin