Ontogenetic Depth

In another thread, Roy wrote about the ridicule which followed my original proposal of “ontogenetic depth” (OD):

The ridicule is self-inflicted and richly deserved.

Indeed. I had only myself to blame. PZ Myers needed simply to step in and point out the obvious. My 2003-4 proposal, that OD could be calculated as the product of the average of cell divisions (between fertilized egg and any cell in the reproductively capable adult), times the number of cell types, was hopelessly wrong.

Nonetheless, I have continued to work on OD since 2003, and today am more persuaded than ever that OD is real and therefore significant for evolution and intelligent design. OD represents the major obstacle to theories of undirected evolution for the origin of the animal body plans.

Evolution fails to explain OD, which is why (160 years after Darwin) the origin of the animals remains an open puzzle. Whether ID explains it depends critically on the ID hypothesis (take note, John Mercer!) on the table.

I am eager to discuss OD, but only with people who have taken the trouble to inform themselves, so – if you want to talk about OD – watch this 2018 talk first, which runs approximately one hour:

Note to Faisal Ali. You prefer to criticize ID people without reading their work. That’s fine. We all have to decide how to use our time.

But I will continue to ignore what you say unless you inform yourself. Watch the talk.

This video is also relevant:

I’ve never really looked into ‘ontogenetic depth’ before, so over lunch I dug out the original presentation and scanned through it.

This caught my eye:

Ontogenetic networks in all animals commence with a single cell, the fertilized egg. Then an unfolding arborescence of developmental decisions begins, whose complexity and overall architecture varies by taxon. In all animals, however, a point in the adult phenotype arrives when reproduction – the generation of gametes capable of fertilization – is possible. This distance, from the egg to the adult capable of reproduction, is what we term ontogenetic depth (see Figure 4). Somewhat more formally, ontogenetic depth may be defined as the distance, in terms of cell division and differentiation, between a unicellular condition and a macroscopic adult metazoan able to reproduce itself (i.e., generate gametes).

The ontogenetic depth of a handful of extant animals (from the model systems of developmental biology) is known with precision.

But what are those precisely known values for ontogenetic depth? The paper doesn’t say. Nor is any formula given. The closest thing to a precise value is this:

In the nematode Caenorhabditis elegans, for instance, a relatively small animal only 1.5 mm in length, 7 to 9 rounds of cell division lie between the fertilized egg and any cell in the adult: 959 somatic cells in the hermaphrodite (with a variable number of germ cells), and 1031 cells in the male (with its distinctive tale). For larger metazoans, of course, such as the dipteran Drosophila melanogaster, ontogenetic depth is much greater, as total cell number, degree
of cellular differentiation, and time to reproductive capability increase accordingly.

But what is the ‘ontogenetic depth’ of C elegans? Is it 7? 8±1? 959-1? 959/9? 1.5? Something else entirely?

Other questions spring readily to mind:

  • Is D melanogaster one of the handful of organisms with a precisely known ‘ontogenetic depth’? If so, what is the precise value?
  • What other organisms have known ‘ontogenetic depth’?
  • How is ‘ontogenetic depth’ actually calculated? What units does it have?
  • What is the male’s tale?

@pnelson later admitted that he didn’t even know how to measure ‘ontogenetic depth’, let alone calculate precise values:

Anyone would agree that there’s a distance between egg and adult in C. elegans. The question is how best to measure that distance, in units (or metrics) that allow comparison with other animal groups.

So the problem isn’t that ‘ontogenetic depth’ wasn’t ready, it’s that @pnelson claimed to have precise values for OD, then promised an explanation (which never materialized), but eventually admitted he didn’t know how OD could possibly be calculated.

The result is self-inflicted.


I can’t find that formula (cell divisions * cell types) anywhere in your original publication.

Perhaps if you’d simply provided that formula 16 years ago, rather than promising replies that never materialized, ‘Paul Nelson Day’ would never have been born.


Perhaps if you’d simply provided that formula 16 years ago, rather than promising replies that never materialized, ‘Paul Nelson Day’ would never have been born.

The formula was present in the original publication (a poster at the 2003 meeting of the Society for Developmental Biology). Here’s the abstract:

65. Understanding the Cambrian Explosion by Estimating Ontogenetic Depth. Paul A. Nelson and Marcus R. Ross. Discovery Institute and the University of Rhode Island, Kingston, Rhode Island.

Various attempts have been made to assess the increase in biological complexity exhibited by metazoans across the Neoproterozoic-Cambrian boundary. These include such metrics as genome size, cell type (Valentine et al., 1994), and several complexity measures (e.g., McShea, 1996). We develop a measure of ontogenetic depth, which estimates the distance, in terms of cell division and differentiation, between a unicellular condition and a macroscopic adult metazoan capable of reproduction (generation of gametes). We apply this metric to the radiative events that occurred during the Cambrian Explosion and evaluate the evolutionary mechanisms that may explain the increases in ontogenetic depth at the origin of the phyla.

See Developmental Biology, vol. 259 (2003), p. 459; emphasis added.

Doesn’t matter, really – the formula is wrong.

But the problem of OD is still real, which is why I continue to think about (and work on) it.

Paul, what is it exactly you think is not being explained? I don’t have the patience to sit through that 1 hour and 20 minutes of video I’m sorry to say. Can you state it in a succinct form? You don’t have to give exact numbers (at least to begin with), maybe you can just give your “elevator pitch”.

Do I have it right that, at least superficially, you are talking about having some measure of organismal complexity, defined in a way that has to do with number of cell types(and here you have some formula for getting a number), and you want some degree of change having occurred on some phylogeny in that measure of complexity (it [increased in this clade A by this much X], and [in that clade B by that much Y], and [decreased in this clade C by this much Z]?), explained by evolution? That it, at bottom?

1 Like

Elevator pitch:

1. Multicellular animals evolved from unicellular eukaryotes (standard theory).

2. If natural selection was the causal process responsible, reproductive capability is essential (standard theory).

3. However, reproductive capability in any animal arises at the end of development (standard theory), after cell number increases and differentiation occurs: this is ontogenetic depth (OD).

This short article on OD won’t take an hour to read:

The YouTube talk, linked above, is one hour; the rest is Q & A.

I’m not a biologist, and perhaps that shows in this comment. However, the quoted assertion seems wrong to me. It seems to suggest that reproductive capability suddenly pops into existence near the end of development.

I would have thought it better to say that reproductive ability is only completed near the end of development. But surely the beginnings of that ability are there early on. So it doesn’t just arise near the end.

The “end of development” is often defined as “onset of reproductive capability.”

But of course you are right that the stage-setting (for that capability) is being laid down all throughout the developmental trajectory.

So over the course of evolution, the number of cell divisions and distinct differentiated cell types have changed on different lineages. Okay, and?


  1. Axolotls
  2. Water fleas
  3. Aphids
  4. Strawberries
  5. Clownfish
  6. Spider plants
  7. Crown-of-thorns starfish
  8. Lichen (maybe)
  9. Any creature that produces monozygotic twins

Very nice, but you seem to be drawing some unstated conclusion from this. Isn’t there a number 4 where you explain why this makes evolution unlikely? You will have to provide that part of the argument, because I don’t see it.


Oh, and somatic cell division can be considered a form of reproduction anyway. Objections along the line of ‘the resulting cells (eventually) can’t reproduce’ can be countered by eusociality, where organisms that can’t reproduce aid the reproduction of those that do. Hypersomaticity?

While I’m musing, does anyone know whether monozygotic twinning is correlated with nutritional availability? I know it isn’t in some cases, since armadillos always do it twice, but it may be in other species.

That would be a claim for which you are ignoring highly relevant evidence.

There aren’t any hypotheses on the table. Hypotheses make testable, empirical predictions and you don’t have them. You appear to be avoiding them.

That seems more than a bit arrogant. Have YOU taken the trouble to inform yourself?

Posters aren’t publications. Only the poster abstract (sometimes) is.

There’s no hypothesis there, but let’s go through it.

Even shorter elevator point: Dictyostelium discoideum:

How can you not know about it? The multicellular phase is a response to starvation.

The life cycle cartoon seems clear to me, but let’s go through it as it pertains to each of your claims:

Wrong if you are referring to a single event. Dicty shows how plastic it can be.

Dead wrong. Dictyostelium reproduces in both unicellular and multicellular modes. Fact, not theory.

I started my scientific career with Dicty over 50 years ago. Why have you apparently never heard of it today?

Completely false for Dicty, which reproduces as both amoebae and at the end of multicellular development. Also fact, not theory. Your premise is objectively false.

OD is still dead meat.

Paul, have you considered starting from actual evidence instead of citing straw-man versions of evolutionary theory in your thinking?


I would disagree. Abstracts are sometimes published in society journals, but I would never consider that to be real publication.

I think I see his attempted point. He’s viewing development as a necessarily long process that must evolve gradually, with reproduction only at the end of development. It’s kind of the “what good is half a wing” idea carried far further. Apparently the intermediate evolutionary stage between protist and human is supposed to be a free-living 12-week fetus. But since the fetus can’t reproduce, evolution must stop at that point. Take that, evolutionists!

I was trying to give him the benefit of the doubt.

I would hope that you see that I see his attempted point. Do you?

Yes, I hope that you hope I see that you see his attempted point. I’m still not quite sure that was his point or that he won’t deny that it was.

To John Mercer:

  1. Dictyostelium is not a metazoan. OD addresses metazoan development.

  2. The evolutionary origins of cell differentiation in metazoans is widely considered an open (i.e., unsolved) problem. In 2003, Carl Schlichting (U of CT) wrote, “How cell types of multicellular organisms came to be differentiated is still an open issue,” a statement that is true today. OD addresses why the problem is unsolved. Dictyostelium, while fascinating in its own right, yields relatively little insight (because of the peculiarities of its life history, when compared to metazoan increase in cell number and differentiation, which is dramatically different even in very small animals such as C. elegans). When I first discussed OD with Ann Gauger, several years ago, she brought up Dicty, and I explained to her why it wasn’t relevant. It still isn’t. (If you think it is, show how Dicty illuminates the origin of the cell lineage of any animal, starting from the fertilized egg.)

Carl D. Schlichting, “Origins of differentiation via phenotypic plasticity,” Evolution & Development 5 (2003):98-105.

I’m seeing a pattern here. Protein-free RNA catalyzing peptide bonds isn’t relevant to ribosomes as ribozymes because [insert reason here], Dictyostelium isn’t relevant to multicellularity because [insert reason here]. There’s always a reason that can be inserted, some difference between anything and what it’s supposed to be evidence for.

But wait, are you saying that only animals have ontogenetic depth? Plants don’t? Algae don’t? And most definitely slime molds don’t?


That’s clear from the forum structure.

Put the goalposts down. You’re going to hurt yourself.

I didn’t claim it was, and you didn’t mention that AFAIK; you claimed that you were addressing “multicellular animals,” with zero justification for doing so in isolation.

Where does Dicty fall on your representation below?

It sure looks like you are claiming a continuum there.

Dicty is the transitional that you pretend doesn’t exist because it can’t exist according to your false claims about “standard theory.” Did anyone else notice that your mentions of “standard theory” had no citations of the alleged standard?

Please name one example of “standard theory” that denies the existence of Dicty. It was discovered 85 years ago.

I agree, but so what? We were talking about the objective falsehood of all three of your premises, which had to do with your false claims about multicellularity and what it did and did not allow.

Well, you merely saying something certainly settles the matter. What you said then doesn’t address the fact that the mere existence of Dicty falsifies all three of your premises presented here, which are straw-man fallacies.

Hint: less French, less Latin, fewer Biblical references, fewer bogus references to “standard theory,” and more data.

I’m talking about how Dicty’s simple existence falsifies each of the premises you presented here, which you falsely attributed to “standard theory” without citations.

Do you really think that these frantic goalpost moves are fooling anyone?


Hey - I’ve broken the mold on this thread by watching the presentation.