The __________ suggests that speciation occurs in spurts.?

Question

. punctuated equilibrium model

b. adaptive model of the origin of species

c. book of Genesis

d. gradualism model of the origin of species

e. theory put forth by Buffon

Answer 1

The "punctuated equilibrium" theory of Niles Eldredge and Stephen Jay Gould was proposed as a criticism of the traditional Darwinian theory of evolution. Eldredge and Gould observed that evolution tends to happen in fits and starts, sometimes moving very fast, sometimes moving very slowly or not at all. On the other hand, typical variations tend to be small. Therefore, Darwin saw evolution as a slow, continuous process, without sudden jumps. However, if you study the fossils of organisms found in subsequent geological layers, you will see long intervals in which nothing changed ("equilibrium"), "punctuated" by short, revolutionary transitions, in which species became extinct and replaced by wholly new forms. Instead of a slow, continous progression, the evolution of life on Earth seems more like the life of a soldier: long periods of boredom interrupted by rare moments of terror.

Punctuated equilibrium is more an observation than a theory of evolution. However, this observation is easy to explain by using some general insights from the systems approach. Consider a typical fitness landscape, in which there are valleys separated by ridges. If the evolving system has reached the bottom of a deep valley, there will be almost no change, since variation will fail to pull the system out of that hole. This is a negative feedback regime, in which chance fluctuations will be counteracted, pulling the system back to its equilibrium position at the bottom of the valley.

On the other hand, if there is only a small ridge separating the valley from a neighboring, deeper valley, then a chance event may be sufficient to push the system over the edge so that it enters the other valley. Such a lucky variation will become increasingly likely when the fitness landscape changes so as to reduce the height of the ridge. Once over the ridge, the descent into the new valley will go very fast. This is a positive feedback regime in which deviations from the previous position are amplified. This means that the system will evolve very quickly to a new, fitter configuration. If we would check the evolution of the species in the geological record, we would find many fossils corresponding to the position at the bottom of the valley where the organism remained for so long, but few or none corresponding to the crossing of the ridge, which happened very fast on the geological time scale.

Answer 2

They've got it. It's A.

Punctuated equilibrium is a period of relative calm followed by sudden spurts of change.

You can think of it using a series of stairs, and this was probably the model your prof used, but some of us object to the idea that this means species evolve to be "higher" and prefer the following representation of the model:

  TIME--->

==========!!============!!==========!!...

It's a good mnemonic, too, PUNCTUATED (!!!!) EQUILIBRIUM (=)

Answer 3

a.

Answer 4

A is correct. Punctuated equilibrium model.

PS Some of your questions above are incomplete.

Answer 5

im thinkin' A