Ranunculus aquatilis
The first part of its’ name identifying it as a part of the Buttercup Genus and its’ second name specifying that it lives in water. The first name is always a noun and the second an adjective.
The relation between Phylogeny and Classification
Phylogeny is the evolutionary history of a species, it is a valuable biological mechanism used to determine what genus a species may fall into, as species which have very similar (homologous) features can be assumed to have evolved from the same common ancestors, e.g. horses donkeys and zebras all have homologous features and can all be filed under the genus Equus.
Artificial selection
Humans have also had a hand in how many of the animals we see every day are the way they are. Take Dogs for example, they have been bred to produce a wide variety of qualities that we find desirable in them, and these can be behavioural, or physical properties. Guard dogs have been bred to have phenotypes such as broad shoulders, heavy build and they also have been selectively bred to be aggressive and territorial other dogs, such as terriers have been bred to be small and fairly docile, ideal qualities for a house pet.
In this case Humans have taken the place of natural selection for the dogs, to tailor them to our requirements. Desirable phenotypes which are recognized in the adult dogs are passed onto the next generation, by breeding them with other dogs, with these same qualities, leading to offspring, in which these phenotypes may be more defined, because the genes of both parents, both containing the allele for the desirable phenotype have combined, making the probability of the offspring having these qualities a lot higher than if the dogs had been left to mate randomly.
Evolution
- How does variation occur in organisms?
Variation occurs in populations for a wide range of reasons, either environmental, or because of the mutations in certain members of the species. Changes in organisms affected by the environment in which they live cannot be inherited by their offspring (or daughter cells in asexual reproduction), as only genetic differences can be passed onto the next generation by the either sexual or asexual reproduction.
The variation caused by sexual reproduction depend on various factors, these are:
- Different assortment of chromosomes in each parent.
- Crossing over of homologous chromosomes during meiosis.
- Random (to a degree) mating between parents (if selective partnering isn’t considered a significant factor).
- Random fertilization of gametes, the sperm, which will reach the egg first is completely random.
- Mutation as a result of change in the nuclear materials in individual organisms, which can be passed on through sexual reproduction.
- Mutations in multi cellular organisms
Environmental factors in evolution
The environment plays a very large role in how evolution takes its course. For example in the north of England there are varieties of dark winged and light winged speckled moths, the numbers of both varieties of moth tended to be very similar. During the industrial revolution large amounts of coal were burned to fuel the many factories in the north of the country, the soot from the burning coal turned the bark of trees near factories a dark black, after this was observed a sharp decrease in the numbers of moths with light coloured wings was noted. This was because the dark moths were very well camouflaged against the blackened tree bark, whereas the light winged moths stood out and were heavily preyed on by birds, this led to the dark winged variety of moth becoming far more successful than the light winged one. When coal was banned for use in factories in England the bark on trees eventually reverted to it’s original colour, after this a return to the relative equilibrium in the numbers of light and dark moths was observed. This example shows how the environment an organism lives in can drastically change the successfulness of varieties of the organism showing a certain phenotype. This is a classic example of environmental factors can affect the allele frequency in a population.
How genetic variation occurs
Genetic variation can occur through the crossing over of` chromatids of the same chromosome during late prophase in meiosis. The chromatids cross at a random point(s) along their length, (the points at which the chromatids cross is called a chiasma, this may occur one or more times along the length of a chromatid) this leads to a greater variation in chromosomes that can be passed on into the gametes of an organism than if crossing did not occur .The randomness of mating, is also a major factor in how variation occurs in populations of sexually reproducing organisms. Environmental factors, like that shown in the last paragraph (when sustained over a long period of time) also play a major role in the genetic variation of a species.
Overproduction.
All species have the potential to overproduce; essentially all population sizes and the factors that affect them are relative. Humans are overproducing now and overcrowding is a major problem in most parts of the planet.
From a very Dawkins point of view the aim of every organism is simply to expand it’s population, for example a female rabbit may have several young in a litter and give birth to several litters a year, if every young rabbit from every litter survived to maturity the rabbit population would expand exponentially. The reason this doesn’t occur is because of environmental factors, which may be biotic (living components of the environment) or abiotic (non-living components of the environment). Biotic factors could be such things as predation, disease, habitat (trees, plants…) and abundance of food… when these factors no longer limit the size of the population then it will begin to expand.
One example of drastic overproduction is that of rabbits in Australia half way through the last century, Rabbits are not native to Australia and they had no natural predators or diseases that would affect their population size and food was plentiful, so their population exploded. They were rounded up and shot in masses, but this had very little effect on their population, eventually the viral disease myxomatosis was introduced into the rabbit population, by man, through infected fleas (the carriers of the disease), since the rabbit population was so dense the disease spread quickly and massive numbers of rabbits were killed, the disease became the only biotic environmental factor affecting their population, but it still greatly decreased their population size.
This case gives a clear example of how environmental factors limit population sizes, if humans were not affected by famine, drought and disease our population would balloon out of control and measures would have to be taken (like those in place in china) to limit the growth of our population.
