I am Rushtonian and Jensenist on many, if not most things. However, when it comes to whether or not evolution is progressive or not, I believe it’s not progressive. It makes no evolutionary sense for evolution to be ‘progressing’ anywhere. As I’ve said millions of times previously and I will still need to say millions of times more, each organism is suited for its environment with Darwin’s Finches being the perfect example of the non-linear, non-progressiveness of evolution. I’ve also had some choice words for Gould and his theories on race, race and IQ and IQ in general. However, just because someone is monumentally wrong on most things, doesn’t mean they are wrong on all things. Punctuated Equilibrium (PE) is a great theory and explains, in my opinion, why there are so few transitional fossils in the fossil record.
Eldredge and Gould (1972) put forth a new theory of evolution called “Punctuated Equilibrium”. In this theory, species are generally stable and only go through swift speciation changes in bursts of time. Since species changed very little, if at all, over millions of years this would leave behind fewer fossils of phenotypic changes in the species.
Charles Darwin understood that evolution was a slow and gradual process. By gradual, Darwin did not mean “perfectly smooth,” but rather, “stepwise,” with a species evolving and accumulating small variations over long periods of time until a new species was born. He did not assume that the pace of change was constant, however, and recognized that many species retained the same form for long periods.
But if evolution were gradual then there would still be transitional fossils. This is one notion that troubled Darwin; if there were no–or hardly any–transitional fossils, is evolution falsified?
The answer is clearly no. This is where Eldredge and Gould’s Punctuated Equilibrium comes in. PE states that species are generally in stasis and hardly go through any phenotypic change over a large amount of time. Species go through little change, according to Gould and Eldredge, over millions of years. “This leisurely pace is “punctuated” by a rapid burst of change that results in a new species and that leaves few fossils behind.” Gould and Eldredge propose that Darwin’s gradualism is nonexistent in the fossil record with stasis dominating the history of most fossils.
This is, in my opinion, one of the best theories for explaining why there are hardly any transitional fossils in the fossil record. Since most species remain in stasis for a long while, phenotypic changes won’t occur and thus we won’t be able to see the speciation in the fossil record because of the long time in stasis. Basically, one an organism appears in the fossil record it remains in stasis for millions of years until it goes through a quick, gradual change. Benton and Pearson (2001) in their paper Speciation in the fossil record state:
An analysis of the results of 58 studies on speciation patterns in the fossil record, published between 1972 and 1995, demonstrates the widespread occurrence of stasis in the fossil record25. Organisms ranged from radiolaria and foraminifera to ammonites and mammals, and stratigraphic ages ranged from the Cambrian to the Neogene, with the majority concentrating in the Neogene, the past 25 million years (My) of the history of the earth. Of the 58 studies, 41 (71%) showed stasis, associated either with anagenesis (15 cases; 37%) or with punctuated patterns (26 cases; 63%). It therefore seems clear that stasis is common and had not been predicted from modern genetic studies. (pg. 408)
That’s pretty amazing. 63 percent of the studies showed punctuated patterns. Clearly, stasis is common in the fossil record. This, in my opinion, answers Darwin’s question as to why there are hardly any transitional fossils. For an example showing the PE in pictures, see Berkely.
Scientists think that species with a shorter evolution evolved mostly by PE while those with a longer evolution evolved by mostly phyletic gradualism. On page 96 of their paper, Eldredge and Gould write:
“In summary, we contrast the tenets and predictions of allopatric speciation with the corresponding statements of phyletic gradualism previously given:
(1) New species arise by the splitting of lineages.
(2) New species develop rapidly.
(3) A small sub-population of the ancestral form gives rise to the new species.
(4) The new species originates in a very small part of the ancestral species’ geographic extent – in an isolated area at the periphery of the range.
These four statements again entail two important consequences:
(1) In any local section containing ancestral species, the fossil record for the descendant’s origin should consist of a sharp morphological break between the two forms. …. we will rarely discover the actual event in the fossil record.
(2) Many breaks in the fossil record are real; they express the way in which evolution occurs, not the fragments of an imperfect record.”
Most of the claims put forth by Eldredge and Gould were controversial to evolutionary biologists when they put their paper forth. However, PE is 100 percent Darwinian and does not contradict Darwinism at all.
The 3 conclusions Eldredge and Gould came to are as follows:
- Species generally remain in stasis.
- All adaptive changes usually correspond with speciation
- NS at the species level has important macroevolutionary changes
In sum, PE was formulated to explain discontinuities between species and not major taxa. This also answers Darwin’s question on why there were hardly any transitional fossils.
Here is a nice picture to show how PE works in contrast to phyletic gradualism (PG):
You can see that in the PE model, a species remains in stasis while in the PG model a species is constantly changing. Looking at the fossil record, as I’ve shown previously, we will see that a great majority of species remained in stasis before a sudden phenotypic change (probably a change in environment forcing this). This is why, in my opinion, there are hardly any transitional fossils. This is the best theory to answer Darwin’s question.