SALTATIONISM: CHARACTERISTICS, EVIDENCE AND EXAMPLES - BIOLOGY - 2025

The saltationism, in evolutionary biology, is a theory of the twentieth century and suggests that the phenotypic changes that occur in lineages during evolution are the result of large jumps marked, without the existence of intermediate variants between biological entities. With the advent of Darwinian ideas and evolutionary synthesis, it was superseded. Thus, today saltationism is considered an idea already discredited.

Within evolutionary biology, one of the most prominent discussions is related to the fossil record. Opponents of evolutionary theory use the fossil record as evidence against it, arguing that it is not possible to demonstrate the small gradual changes proposed by Charles Darwin in 1859.

Source: Biodiversity Heritage Library

Different theories have arisen to explain its discontinuity and one of them is saltationism. This view attributes the origin of new species and adaptations to rapid and dramatic changes.

Defenders

Hugo de Vries contributions

One of the defenders of saltationism and mutationism (a "subclass" of saltationism, to call it somehow) was the botanist Hugo de Vries, whose contributions are notable in the area of ​​genetics.

This researcher proposes that Darwinian gradual variations are just non-heritable fluctuations, and species emerge rapidly, markedly and non-adaptively in simple, large steps. This model implies that there are no transitional forms between species.

For Vries, the role of selection is limited to eliminating aberrant and deleterious mutations that may arise in the population.

Richard Goldschmidt contributions

Perhaps the name most associated with saltationism is Richard Goldschmidt. Under Goldschmidt's perspective, "true" species are separated by spaces that can only be explained by saltationist-type changes - and not by orthodox Darwinian gradual changes.

Note that Goldschmidt's vision was directed at macroevolutionary changes. He did not doubt the importance of gradual microevolutionary variations - that is, at the species level. The "jumps" were applied to explain the abrupt appearance of higher taxa.

Macromutations and

These large changes were called macromutations, to refer to mutations with very significant phenotypic effects.

Goldschmidt accepted that most of these macromutations were deleterious to their wearer and gave rise to "monsters." But from time to time, a variety might emerge that was adapted to a new way of life. Hence the famous term is born - among the saltationists of "hopeful monster".

Mechanisms

Goldschmidt proposes two mechanisms to explain the origin of these monsters hopefully. The first assumes a different arrangement of chromosomes, which he called systematic mutations. According to this model the emergence of new species would not take long.

The authorities of the time rejected this view, as it refuted the traditional concept of gene. In fact, this reasoning fostered what little credibility Goldschmidt gained.

The second mechanism was based on developmental macromutations, which occur very early in the life of the organism. This type of mutation is congruent with the traditional concept of gene, which is why it received greater acceptance in the scientific community.

Today, the second mechanism is highly related to evolutionary developmental biology, informally abbreviated as "evo-devo." One of the proposals of this branch of biology is that morphological novelties can arise through changes in a few genes - which generate great effects.

Some authors suggest that the evo-devo proposals are helping to resurrect the Goldschmidt monsters.

Other defenders of saltationism

William Bateson, Carl Correns, Karl Beurlen and Otto Heinrich Schindewolf were eminent geneticists who defended saltationist ideas.

Differences with gradualism

What does "gradual" mean?

Before contrasting gradualism with saltationism, we must define what we are going to consider as gradual change. According to the famous evolutionary biologist Richard Dawkins, the term gradualism has two meanings.

The first is related to evolutionary rates - where it can also be called phyletic gradualism. In this sense, gradualism exposes evolution as a constant process over time and species arise in this same context, without a change in rate or a special event during the separation of lineages.

A second meaning for the term gradual has to do with the generation of biological adaptations. In The Origin of Species Darwin repeats - very emphatically - that complex adaptations, such as the eye for example, were formed starting from small gradual changes in multiple intermediate states.

Gradualism vs. saltationism

Now, contrasting gradualism with saltationism, for the former the gaps in the fossil record represent how imperfect it is - if it were much more complete, the transitional forms would be observed. For the latter, such forms never existed.

For a saltationist there was a moment when an individual so different from his parents emerged that he was instantly isolated. This is a very strange case, although it can occur in plants by the event of complete genome duplication and would be a kind of "instantaneous speciation."

Some authors argue that the evolutionary scenarios of gradualism and saltationism are not mutually exclusive. In contrast, both must be evaluated and taken into account to explain the complexity and enormous diversity of organic beings.

If the reader wants to expand his knowledge on the subject, he can read Dawkins' essay in The Blind Watchmaker entitled "Disrupting Interruptions", where this author describes in depth the different hypotheses raised related to this subject.

Differences from punctuated equilibrium

One of the most frequent mistakes is to confuse the theory of punctuated equilibrium with saltationism. Although very superficially they may look similar, the two proposals differ profoundly in the way they explain the discontinuity of the fossil record.

What is punctuated equilibrium?

Punctuated equilibrium is a theory proposed by Stephen Jay Gould and Niles Eldredge in 1972. These authors seek to give a new vision and explain in an alternative way the discontinuities of the fossil record, applying traditional models of speciation.

The theory proposes two states or patterns of change for species. One of these is stasis (not to be confused with "ecstasy") and the other is punctuation or rapid changes. That is, we no longer assume a constant rate.

In the stasis periods the species do not undergo significant changes, while in the scores the changes are accelerated and overlap with the speciation events.

As the allopatric model of speciation suggests a spatial separation within the event, we should not expect to find a perfect and gradual fossil sequence - simply because speciation does not occur in the same place.

Scored Balance vs. Saltationism

For the defenders of punctuated equilibrium, the intermediate forms are not found due to the geographic separation that allopatric speciation implies. In contrast, saltationists argue that intermediate forms never existed.

Evidence and examples

Today, saltationist ideas have been discredited and abandoned by most modern biologists, thanks to poor evidence and a lack of examples - among other factors.

It is true that macromutations do occur. However, what is disputed is that such mutations with such marked effects on the phenotype may have an effect on evolution. One of the staunchest opponents of this theory was Fisher.

References

1. Audesirk, T., Audesirk, G., & Byers, BE (2004). Biology: science and nature. Pearson Education.
2. Bateman, RM, & DiMichele, WA (1994). Saltational evolution of form in vascular plants: a neoGoldschmidtian synthesis. In Linnean Society, Symposium Series.
3. Darwin, C. (1859). On the origins of species by means of natural selection. Murray.
4. Dawkins, R. (1996). The blind watchmaker: Why the evidence of evolution reveals a universe without design. WW Norton & Company. Freeman, S., & Herron, JC (2002). Evolutionary analysis. Prentice Hall.
5. Futuyma, DJ (2005). Evolution. Sinauer.
6. Gunter Theißen (2009). Saltational evolution: hopeful monsters are here to stay. Theory Biosci, 128, 43–51.
7. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). New York: McGraw-Hill.
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