• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

What is a species? How do new species arise? What is the difference between the graduated and punctuated theories of speciation?

Extracts from this document...


What is a species? How do new species arise? What is the difference between the graduated and punctuated theories of speciation? Speciation and evolution are topics in biology which are contentious and open to debate. New evidence is continually being found which reshapes our ideas about the mechanisms and patterns of speciation. There is much controversy over many aspects of this topic, from the question, 'what is a species?', to the pattern in which these new species arise. Darwin was the first to powerfully attack the idea of creationalism in 1959, and since this date his theory of evolution by natural selection has dominated. Darwin sparked an explosion in research in this area, and in 1972, Niles Eldredge and Stephen Jay Gould put forward the idea of punctuated equilibrium. This suggested that evolution was not a slow continuous additive process as Darwin had thought. The theory of punctuated equilibrium states that there are long periods of time where little of no morphological change occurs, punctuated by short periods of rapid change in which speciation occurs. As the fossil record grows, and more theoretical research is done, we will be able to more accurately a***s the importance of Punctuated equilibrium as opposed to gradualism as the theory of speciation. There are many different definitions of the term 'species'. Creationists believe that species are discrete fixed entities, and that their form has not changed since their creation. ...read more.


It is likely that the founder population will have a gene pool which is not representative of the ancestral population, as it is likely that there is something distinct in that population which caused them to found a new population. Random chance will also cause bias in the selected gene pool. Adaptive radiation causes genetic divergence as the population isolated in the novel environment will be subjected to different selection pressures and therefore undergo rapid adaptation. Genetic divergence eventually causes reproductive isolation, as the two populations have diverged so much that they can no longer successfully interbreed. b) Sympatric speciation - this occurs without geographical isolation. Sympatric speciation is far less common than allopatric speciation, as gene flow is still possible between the two populations. There are two modes of sympatric speciation, the first of which is ecological speciation, whereby the population is not separated by a geographic barrier, but by an ecological one which prevents gene flow between the groups. For example, different forms of parasites of the same species may live and reproduce in different hosts, and there will therefore be no gene flow between the forms reproducing in different hosts. There is therefore assortive, rather than random mating. Due to the lack of gene flow, natural selection and genetic drift will eventually produce two reproductively isolated species. The second mode of sympatric speciation is strong disruptive selection. If the two extremes of a trait are strongly selected for, and the hybrids have reduced fitness, then successful reproduction between the two extremes will be reduced and gene flow will be minimal. ...read more.


Punctuated Equilibrium is more of an observation of evolution than a mechanism. It has been noted that adaptive radiations tend to occur following mass extinction events. For example, the extinction of Dinosaurs allowed the adaptive radiation of mammals. It is thought that the extinction freed ecological niches. Allowing mammals to diversify and fill these niches. The theory of punctuated equilibrium is an alternative to Darwin's (1959) belief that evolution was a slow, continuous and gradual process without sudden jumps. This theory is known as phyletic gradualism, and has been the widely accepted theory of evolution throughout the late 19th century and most of the 20th century. However, it was gradually realised that there was overwhelming evidence from the fossil record and theoretical studies that punctuated equilibrium is the foremost pattern in evolution. There is however, some fossil evidence supporting phyletic gradualism. One group of fossils which provides support for phyletic gradualism is the foraminifera fossils. By examining marine plankton fossils which appear in the Paleocene and extending 66 million years, Hunter et al. (1988) demonstrated a nearly continuous morphological change through time. However such evidence is scarce, and seems to be apparent in only a few taxa. Punctuated equilibrium seems to explain the jumps in morphological forms observed in the fossil record, and studies have provided evidence that evolutionary processes can and do incite this pattern. Although phyletic gradualism is evident, it is seen to only be important in a few taxa. The evolution of life has been shaped by both punctuated equilibrium and phyletic gradualism, but current data suggests that punctuated equilibrium plays a more significant role. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our University Degree Zoology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related University Degree Zoology essays

  1. Marked by a teacher

    What is a species?

    4 star(s)

    Firstly, this concept can only be applied to s****l reproductive organisms and therefore can not be applied to asexual organisms or fossilised extinct organisms: "Where we have s****l reproduction a species can be objectively defined as a group of organisms which reproduce s******y amongst themselves but don't reproduce with members of other species.

  2. Analysis of Charles Darwin's theory of origin of the species

    However there are many arguments about his thoughts. Many people do not take the theory of evolution as their choice of doctrines. Instead they believe in Creationism or a hybrid of the two in which God assisted evolution. To these people, Darwin's theory of Natural selection and evolution is full of holes.

  1. Charles Darwin and his Theory of Natural Selection

    The English vice-governor of the Galapagos Islands told Darwin that even within the archipelago, there was noticeable variety. The tortoises on each island were slightly different, so that it was possible to tell which island that they came from. Those that lived on relatively well-watered islands where there was ground

  2. Horse Evolution

    The Miohippus population that remained on grasslands developed into the Parahippus, which was approximately the size of a small pony.

  1. Comparing the Processes of Osmoregulation ...

    In the presence of Antidiuretic Hormone (ADH - secreted by the hypothalamus), which increases the water permeability of the colecting ducts, hyposmotic fluid that enters the distal tubule from the ascending limb looses the majority of its water as a result of osmotic equilibration.

  2. The positive correlation shows that the older the molehill the higher the species diversity ...

    This process disturbs the plants rooted on the ground before the molehill was formed and there are only three ways for plants to re-establish themselves on the raised mound of soil. The first way is for buried plants to force their way up through the soil and re-establish themselves.

  1. "Discuss the strengths and weaknesses of Ecologism as a new ethic."

    According to ecologists, "these are elemental truths that we forget at our peril."2We have separated ourselves from nature, and we think of vegetables and meat as commodities, rarely pausing to reflect upon what makes these things possible and available to us, or of how much we depend on them, and they on us.

  2. Investigating the effect that group size has on the vigilant behaviour of flocks of ...

    the logged values of the group size and the percentage looking plotted and also figures 5, 6, 7 and 8 which are the total number of birds against group size and their logged values respectively. All of the above figures have highly significant correlations which are all negative (table 1).

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work