A New Model of Evolution


Evolution over short genetic distances mostly involves simple, easy-to-alter changes of phenotypes. But over large time scales and genetic distances, new materials and body plans accumulate, which are harder to evolve. Only evolution of new, hard-to-accumulate traits produces effects that are often not apparent over the shorter distances. The new model explains these effects in ways that can better account for major changes in evolution, such as the origins of new species and phyla, the origin of major novelties such as sex, plus the causes of human evolution and behavior.

This site is to popularize the new approach, and invite suggestions or corrections for improving the model. 

News Flash

My book is published!!!


At last, my book has now been published! You should be able to get it on Amazon by clicking the icon. Or see the home page at;


However, the important items on this site are free, including the crucial essays that explain the Theory of Options. Please browse through the site. If you have any problems, contact me by email at; mailto:sgould@mozart.inet.co.th.

Note: my book is about the evolution of human behavior, but about 20% of it concerns evolution. It was while working on my book that I came up with the new model described here. All the web pages here are not part of my book directly, and are freely available, but some details might be out of date. The web site equation or the PDF file at model show the most difficult and controversial chapter in the book, though this one chapter is quite technical. The rest is the original site, before the book was published.

Principle Contentions

  1. In any evolving system, some properties are easier to alter than others. (See Theory of Large Changes.)
  2. Genotype fitness will fall for large increases of lineage complexity. (See Theory of Complex Accumulations.)
  3. Large changes tend to accumulate in peripheral niches. (See Peripheral Niche Mechanism.)
  4. Evolution of some traits will saturate above certain levels of complexity. (See Theory of Phylogenic Evolution.)
  5. Large-scale gene flow is radial rather than serial. (See "Smart Gene" Hypothesis.)
  6. Large-scale changes can be best explained on a two-axis model of evolution. (See Two-Axis Model of Evolution.)

Where to Next?

Brief Outline


The Evolution Essays

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1. This is a Darwinian web-site, differing in details, but upholding evolution. This site is to invite comments from people knowledgeable about evolution. For general debate on evolution visit refer to "The Talk-Origins" or related web-sites.

2. There is now a Quotations Page which people might find interesting.

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Where to Next?

I am "new" to evolution. Can you explain what this is about?

Processes of evolution such as mutation or selection act continuously, but the fossil record indicates that many large changes were discontinuous or "stepped".

I understand the issues, but why would some traits be easy, but others hard to evolve?

The asymmetry exists in pre-biotic properties of the universe. These are inherited into early life as basic properties of life, and complex life in turn inherits these as fitness constraints and pathways.

You claim that hard-to-alter traits saturate, but how could this work?

All organisms compose of both easy and hard to alter traits. Easy-to-alter traits are continuously variable, and never saturate, so the relative variation of organisms never saturates. But hard-to-alter traits, the base homologies of organisms, often evolve once only at a fitness cost. Within a given system this closes the fitness path by which these homologies could evolve again. (Only nothing is final. Life could be wiped out and start over, so even DNA could evolve again.)

But why are not all traits encoded in DNA easy to evolve?

DNA encodes many attributes. Some, like polygenic traits or allele combinations, or unexpressed sequences, can change easily once per generation. But DNA sequences expressing the basic homologies of life are hard to evolve, and held in tight fitness trajectories throughout most life.

How does the new theory explain sex, evolution of phyla, or human evolution?

The new theory provides a logical model. Details (facts) must come from research. But it is easier to visualize large-scale changes with the new model, which offers some original hypotheses.

So, why has no one thought of all this before?

It was always known that traits would easier than others to evolve, but to appreciate the full impact of this involves several unfamiliar ("queerer than we can suppose") concepts, which must be worked out first.

Brief Outline

Models of large-scale changes in evolution have been difficult to develop in detail. Most large changes (such as evolution of new phyla or classes) were in the past, and cannot be observed as living evolution. Plus many large ecological effects (such as an asteroid strike, climate change, or making or breaking a land bridge) occur randomly and cannot be modeled. Even so, we assume that as a basic model, over time small changes summate into larger ones.

Yet, the summation of small accumulations into large ones over time is not always a linear. There are several (now much debated) reasons for this.

  1. The "Illusion" of Scale: If eukaryote life evolved in 100 million years (myrs), increasing complexity by a factor of 100 in that time, the accumulation is still incremental. Only if we drew the change on the time scale of life (four billion years) it would appear as a "step" because of the scale. Yet most large changes in life show this step effect over large scales, and we need to explain why. (We know about the scale illusion. We must explain why organisms retain stable states for long periods, then evolve rapidly in short periods, and revert to a new form of stability at a more complex, newly evolved level.)
  2. Large Ecological Change: Some random ecological events (asteroid strike, climate change, land bridge, etc.) have an inherent stepped effect. But even for gradual change, ecological systems tend to be self-stabilizing. Gradual changes accumulate against the tendency of the system to maintain its state, until a catastrophic level of build-up overwhelms the stabilizing mechanisms (the so-called "Gaia" effect).
  3. Population Dynamics: It is disputed, but significant evolution might only occur among small, reproductively isolated populations or after a severe bottleneck, to allow new genes to sweep to fixation. So once an interbreeding population grows above a certain size, it will tend to self-stabilize around a genetic mean, rather than the whole population evolves in a preferred genetic direction. This will produce a "stepped" effect in the fossil record, because when populations are small, individuals will continue to evolve. But once a majority of individuals evolve into fit, adaptable types, the population will diffuse, and stop evolving. (A more contentious part of this dispute is that it will be easier to find fossils from a large, stable population than a small, rapidly evolving one.)
  4. Emergent Complexity: This is a new theory that complexity itself will tend to settle at 'levels' rather than increment in small continuous steps. This means that though complex novelties might accumulate slowly, a new form will not 'emerge' until some minimum threshold of prior complexity has already accumulated. This is a popular theory now, but hard to reconcile with existing models of gene flow.

Onto these four known mechanisms of stepped increases of complexity, the new theory considers a fifth effect. This is that in life and the universe, some properties are easier to alter than others.

Now there are numerous examples, in life and the universe, of why some properties are easier to alter than others, so this is well known. But the significance of it, often overlooked, is that this will provide a very strong "directional" bias to gene flow. We like to think that once traits are encoded in DNA, because DNA can alter easily, adaptation of traits is equally likely in any direction. But what we find is that genes expressing the basic homologies of life are held in very tight fitness trajectories. While it is only genes that express variable, homoplastic traits, (or non-expressed DNA) that alter frequently and without directional bias. However, this further bias to gene flow will also give a stepped effect to large-scale changes, and a very powerful one. Roughly, organisms will always attempt to adapt the easy-to-alter attributes first. (Organisms say, will always alter DNA sequence, rather than evolve a new code). So, only after all the easy-to-enact changes have saturated for a given level of complexity, would new, hard-to-alter traits be forced to evolve. We can show (with some qualifications) that this is a pattern of all evolution.

Yet, this tendency of traits to be either easy of hard to alter is not the sole cause of stepped patterns to large-scale evolution, but it does provide a simple and elegant model of it.

  1. Unlike say, the property of emergent complexity, which is hard to model, the property of traits being easy and hard to alter is fundamental, and exists in all things.
  2. A directional bias to gene flow will cause a stepped pattern to large-scale evolution regardless of ecological change, which will also be easier to model.
  3. Other explanations of the stepped patterns of large-scale change seem to be "against" models of gene flow, which are still the most successful explanation of evolution in other areas. But the new model is also one of gene flow, it is just that the flow is now 'two-axis' (in the direction of easy and hard to alter traits) rather than say the single axis model.

The remainder of this site will explain how the new model works.


Use search engine to navigate entire site, including articles on human evolution and behavior.

Full Index of Essays

Note: PDF versions of these files can be provided on request.


Main Articles

1.0 The Theory of Large Changes 2.0 The Theory of Complex Accumulations

3.0 The "Peripheral Niche" Mechanism   4.0 The Theory of Phylogenic Evolution

5.0 The "Smart Gene" Hypothesis   6.0 A 'Two-Axis' Model of Evolution

Ancillary Articles

Large Scale Changes Use of Terms Primitive Life  Stepped Changes "Behavior First" Complex Time 


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Valid criticism of the "New Model of Evolution" is always most welcome. Especially valuable;

Often I am asked about my research background. This is only a philosophical treatise. I am depending on feedback (from readers) for any criticism about items that are unclear or need further clarification. You can contact me directly by e-mail to seek further information.

mailto:sgould@mozart.inet.co.th (This is my private mail.) Or mailto:sgould@unocal.com (This is a work address, so please restrict correspondence to important matters only.)

To find out more about me, you can visit my personal page.

Revised: 28 Dec 2000