Developmental Bias Add "directionality" to evolution?

I am attaching a report of a workshop on “Developmental Bias” and its impact on evolution.I found the article well written,accessible and informative.
So thought i would attach it for the community.
It has an interesting conclusion below.

Call it bias or not, the many examples presented at the workshop (only some of which are mentioned here) make it clear that there is a highly non-uniform distribution of variability in biological organisms, largely due to their developmental processes. Several of the examples also make it clear that this has direct consequences for the course of evolution, possibly resulting in directionality in evolutionary change, in particular along a path of developmental preference. This certainly seems to challenge the standard view of uniform variability, and natural selection being the only source of directionality in evolution.


I don’t think there is any controversy over the idea that evolution is a contingent process. Features that the organism already has will tend to make some adaptations more easily reached than others. For example, it appears that the ancestors of birds had both flow through lungs and feathers. Both of these features were later adapted to flight. Bats didn’t have this starting set of features. Instead, bats evolved a more efficient hemoglobin to deliver more oxygen to their cells, and they evolved a different wing because they lacked feathers.

Is there any biologist who has ever proposed that variability is uniform? If not, I’m not sure what the EES people are getting at. They seem to be attacking a strawman.


I don’t think they are talking about contingencies in evolution. Their point is that the sequence in which Organisms develop as embryos acts as a filter in allowing some mutations through and filtering out others.
This indicates that some kind of phenotypic “expressions” are preferred over others.
I find that very interesting.

Edited: This would indicate (to me) that there is some kind of boundaries established by the development process to evolution.

Those are contingencies. Beneficial mutations are contingent on the already existing developmental pathway.

That’s correct. There is nothing controversial about this concept, and it has been part of the theory for quite some time now. This is why the EES crowd is often criticized. They will reword things that are already a part of the theory and act as if they have discovered something new.

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This would indicate that some change in the developmental sequence has to happen before a major change in phenotype like what is seen above the family level.

I don’t buy the theory that intentionally reword things that are part of the “theory” to get credit for a “new” discovery.
You can’t keep saying everybody who disagrees with you have problems with integrity, while everyone who agree with you are paragons of virtue.

Small changes over time can accumulate until you have the differences seen between species in different families. You need to remember that taxonomic families are a human invention that don’t exist in the real world. In fact, I would argue that divisions between taxonomic families has more to do with extinction than anything else. The reason that we see large differences between families is due to either extinction of lineages that carried the transitional states or loss of those transitional states.

The point is the EES group already agrees with the theory of evolution.

Except there is little evidence for this…

Developmental bias could easily explain the divisions between “taxonomic families”…
And it seems testable. Further research in the field could find evidence to support or discard the idea.

On the other hand, the fossil record seems more or less complete and the gaps between families remain.

They don’t see it that way… and they spell out their points of disagreement with MS clearly.

How did you reach this conclusion?

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Every time we find transitional fossils it is confirmation of what I am describing.

I agree. What I was saying is that we don’t need large jumps. Small ones will do.

Your claim is disproven every time we find a new fossil species. The fossils in our fossil collections represent a tiny, tiny percentage of the species that have existed on Earth.

Those are points of agreement.

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Except that there is not much evidence for said small steps.
You say there are far more species that went extinct than there are fossils. How do you know this? What evidence do you base this claim on?
And even if this is true, how do you know these species cover the gap between families mad leave a more uniform distribution of phenotypes?

Sure there are.

We have only searched a tiny, tiny fraction of the fossil bearing strata on Earth. On top of that, new fossil species are found all of the time.

How do you know that there aren’t? You are the one claiming that our fossil collections are complete. Where is your evidence?


We are talking about the space between families and you are showing me this?

At best you are making a claim on a supposition without much evidence.
While at the same time rejecting another perfectly feasible explanation that can be investigated more directly.
This doesn’t make any sense. Why protest so much if developmental bias is part of MS? You should be happy to have a possibly better explanatory framework to show why some missing links are not needed.

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Taxonomic families are a human invention. They don’t exist in reality. If I wanted to, I could put chimps and humans in different families.

Right back atcha. You are claiming that our fossil collections are complete without a scintilla of evidence to back it.

How do you explain the fact that we find new transitional fossils all of the time? If our fossil collections are complete, this shouldn’t happen.

We are protesting their claims that they have found something new.

Say again? Where did that come from?

Sure… and people would disagree with you and correct you.
Unless you are claiming the classification into taxonomic families is arbitrary and baseless.

This is a red herring. Do you expect to find enough transitional fossils to fill up the gap between families.

It seems that even if they have not found something new, they ascribe more significance to such observations that you do.
Probably because they view the process of evolution in a different manner than you do.

It’s pretty clear to me that you haven’t bothered to look at sufficient evidence to make such a claim.

  1. Only around 70% of rocks on earth’s surface promote fossilization (most of this is marine). So many animals in Earth’s history have lived in areas where chances of fossilization is poor. That’s why we have more marine fossils then terrestrial. That and marine animals are more likely to fossilize.
  2. Only a small portion of fossil bearing rocks are exposed
  3. We only have access to a small percentage of the exposed rocks. Things like war, government, and property owners make this so. I’m currently experiencing this with a property owner. He won’t let me on.
  4. Have to find the outcrops before they are eroded away.
  5. On top of that, even if conditions are perfect for fossilization, so much still has to go right.

It’s very probable that what we see if a very small percentage of what has actually lived.

Note: edited because I had a percentage backwards. Oops

I live in the area that has the most fossil species in the United States. And it still isn’t that much.

The taxonomic levels are arbitrary. That’s the whole point.

It isn’t a red herring. You claimed that our fossil collections are complete. Are you retracting that claim? If not, you need to give us evidence demonstrating that we have found a fossil for every species that has ever existed.

That type of statement will elicit 5 minutes of eye rolls from most scientists.

Of course there is. We have the fossil record, which frequently shows intermediate states.

Accent on “less”. Here’s my favorite relevant fact: half of all dinosaur genera are known from a single specimen. Do you think you could estimate from that how many are still unknown, still missing that one specimen?


He’s claiming that the rank “family” is arbitrary and baseless, which it is. Perhaps you’ve heard of “lumpers” and “splitters”?