More Darwinian appeals to engineerless engineering?

 Fruit Fly Eyes and More Surprises for Darwin

David Coppedge

Those tiny, pesky fruit flies have gotten no respect. Sprayed, swatted, and irradiated, the little flying machines have been treated by humans as better off dead. Hermann J. Muller got a 1946 Nobel Prize for blasting Drosophila melanogaster fruit flies with X-rays, finding that the barrage gave them lethal mutations. Scientists have manipulated their genes to make them grow legs out of their antennae or grow four wings, rendering them helpless. And worried farmers have convinced politicians to spray malathion over cities like Los Angeles to prevent invasions of fruit flies. But before killing off all these critters, it would be worth taking a closer look at their design.

Eyes’ Size

An adult fruit fly emerges from the egg and pupa in about two weeks. As the eyes are developing in a fruit fly embryo, an amazing process unfolds. A wave of signals sweeps across stem cells in the budding compound eye, switching on certain progenitor cells to stop proliferating and become unit eyes (ommatidia) and signaling others to undergo programmed cell death (apoptosis). The result is an “organ of extreme perfection” to call on Darwin’s phrase that is not only geometrically beautiful but functional for the fly — and it comes in matching left and right sides, like a pair of rubies.

Navarro et al. published a paper about how this works in PLOS Biology. In the same journal, Marco Milán from the Barcelona Institute of Science and Technology summarized the paper, explaining how the regulated process achieves “size precision” as the eye grows. Internal controls reduce “fluctuating asymmetry” (FA), a wobbly mismatch of size and shape. In effect, the growing cells of the eye do The Wave.

A new study unravels an organ-intrinsic mechanism of growth control in the developing fly eye that confers size precision through feedback interactions between proliferating and differentiating cells. This mechanismreduces eye size variability between and within animals, thus contributing to the symmetry between contralateral eyes and having a clear potential impact on eye functionality. In the growing eye primordium, a wave of differentiation moves anteriorly, whereby proliferative progenitors located anterior to the wave are recruited as differentiating retinal cells that exit the cell cycle (Fig 1). When the wave reaches the anterior-most region of the primordium, no remaining progenitors remain in the tissue, and the final eye size is attained. The movement of the differentiation wave relies on the activity of 2 morphogens [shape generators], the BMP homolog Dpp and Hedgehog (Hh), which are produced by differentiating retinal cells that signal anteriorly to nearby proliferating cells to recruit them as new differentiating retinal cells. 

The Barcelona team calls this “feedback control of organ size precision mediated by BMP2-regulated apoptosis.” The result is a geometrically perfect oval-shaped eye with 800 ommatidia neatly arranged like hexagonal cells on a curved honeycomb. The curved shape gives the fly greater than 180-degree visibility on each side. 

Much more must be going on, because bristles grow between each ommatidium to provide touch sensation for the fly, and each unit must be wired properly to the optic nerves going to the developing brain. What’s more, the two eyes must become exact mirror images of each other to prevent fluctuating asymmetry so that the fly can navigate with precision. The authors believe a similar process controls wing development so that the wings match. Imagine a pilot trying to maneuver a plane with one wing shorter than the other!

This one example illustrates an astonishing amount of control in an insect just a few millimeters in length. And they only investigated this in one organ — the visual system — while all the other body systems are also in the process of developing simultaneously: circulation, digestion, reproduction, muscular, flight, sensory, jointed appendages, and much more.

The authors, Navarro et al., make a logical mistake in how these controls came about:

Three features should have resulted in a strong evolutionary pressure to maximize the precision in eye size: First, size impacts vision directly, as image resolution and contrast sensitivity is proportional to the number of light sensing units in the eye; second, making and maintaining the eyes is energetically very expensive, so there is a pressure to match eye size to vision needs; and third, left and right eyes must survey a symmetrical part of the space, so eye asymmetry, which could be driven by developmental noise, should be minimized.

An unguided, blind process could not care about what “should” be done and is incapable of being pressured to do anything. Stephen Crane once quipped, “A man said to the universe: ‘Sir, I exist!’ ‘However,’ replied the universe, ‘The fact has not created in me a sense of obligation.’” Much less could molecules know about or care about “evolutionary pressure.” The authors are admittedly surprised how all these parts come together so neatly:

Biological processes are intrinsically noisy, and yet, the result of development — like the species-specific size and shape of organs — is usually remarkably precise. This precision suggests the existence of mechanisms of feedback control that ensure that deviations from a target size are minimized.

Right Flight

Here’s another fruit fly trick from recent news. How did the fruit fly make a sharp turn? This is not a joke. Sharp turns don’t just happen in a fruit fly because it has wings. They are controlled by specialized neurons. 

This month, Ros et al. published their findings in Current Biology about “Descending control and regulation of spontaneous flight turns in Drosophila.” In the same issue, Matthieu Lewis summarized the research about how and why fruit flies make sudden zigs and zags while flying.

Upon detecting an attractive odor plume, a fly surges upwind, followed by crosswind casting separated by counterturns when the plume is lost. While the sensory control of turning and casting is shared across most animals, little is known about its neural underpinnings. In a paper in this issue of Current Biology, Ros et al. report the identification and functional characterization of a pair of bistable descending neurons that orchestrate casting during flight behavior in the fly Drosophila.

These neurons, Ros et al. explain, consist of “couplets of one excitatory and one inhibitory descending cell form functional units.” As with many systems in biology and in engineering, an accelerator is paired with a brake, providing fine control with a push-and-pull combination of systems responsive to input from the surroundings. Particular “command units” of descending neurons enable a fruit fly to make sharp turns called saccades. “An array of excitatory and inhibitory neurons provides input to the saccade network,” the authors say about one of their major findings.

Within the central nervous system of insects, descending neurons (DNs) constitute a critical stage in the transformation of sensory input in the brain into motor commands in the ventral nerve cord (VNC). Drosophila possess ∼650 pairs of DNs, some of which appear to function as specialized command neurons for specific behaviors, including courtship, walking backward, turning, take-off, and landing. Thus, DNs provide a logical starting point for investigating the circuits that generate and regulate flight saccades.

Stop for a moment to picture this little millimeter-range creature containing 650 pairs of descending neurons each programmed for specific commands. One fires, and the fly walks backward. Another fires, and the fly comes in for a landing. Another fires, and boy fly courts girl fly. This sounds much more astonishing than a computer-controlled robotic drone. 

By ablating one or the other of the descending neurons (DNs) involved in saccades, the team supported their hypothesis that the couplet functions as a saccade-generating unit (SGU). 

The altered saccade dynamics and temporal distribution after ablation support the hypothesis that each DN can produce saccades independently of the other but with different dynamics than those of control flies. The results support a working hypothesis that the two DNs play complementary roles by activating different components of the motor circuit in the VNC responsible for generating saccades. Together, functional imaging, unilateral activation, and ablation experiments suggest that two pairs of descending interneurons, DNae014 and DNb01, function together as saccade-generating units (SGUs) to execute commands for spontaneous turns during flight.

Louis gives examples in other animals, from insects to mammals, that use a similar “sector search” strategy during navigation. But why would a fruit fly need to make a sharp turn?

Saccades are thought to benefit flying animals in several ways. From a sensory perspective, saccades may restrict the deleterious effects of motion blur to brief moments interjected within longer sequences of gaze stabilization. Brief bursts of saccades in the same direction may aid local search strategy by allowing the animal to quickly scan the local environment for salient visual and olfactory features. More recently, it has been suggested that comparing sensory measurements immediately before and after each saccade might enable flies to estimate key parameters that are otherwise not directly measurable, such as the direction and magnitude of the ambient wind. For all these hypotheses, the timing between saccades is critical…

Critical timing, fine control, and convergent strategies between unrelated animals — such concepts defy Darwin’s bluffing notion of the creative power of natural selection. At one point, the authors acknowledge that this looks like engineering.

The activity levels between the left and right DNae014 cells followed an inverse, highly non-linear relationship, analogous to “flip-flop” components in digital electronic circuits (Figure 1J) and reminiscent of neurons identified in the steering behavior of male silkmoths. Further, the DNb01 cells synapse directly onto contralateral DNae014 cells. This is a simple reciprocal inhibitory motif, consistent with a network responsible for binary 

More to Come

We’re not done with design in fruit flies. Next time, we will look at some of the sensory apparatus within these little insects. While fruit flies are convenient lab animals for study, undoubtedly similar systems can be found in even smaller flying insects like mosquitoes and gnats, all of which, being heavier than air, “evolved” powered flight and all their related systems because of “selection pressure.” Not.

In pursuit of a third way.

 Bad News for the “Theist on the Street”

Stephen Dilley

Is mainstream evolutionary theory compatible with a biology-based argument for intelligent design? That’s the argument of theologian Rope Kojonen’s book, The Compatibility of Evolution and Design (CED). Kojonen contends that evolution (and biology) rightly understood actually point to design. His book is perhaps the best treatment available of design and evolution from a theistic evolutionary point of view. But does it succeed?

Casey Luskin, Brian Miller, Emily Reeves, and I have published a peer-reviewed article that analyzes Kojonen’s proposal. Here I will provide an epistemological critique. We’ll see that Kojonen’s model undermines itself by raising obstacles to design detection — including the very design detection that he uses to undergird his own design argument. 

Kojonen defends the perspective of what he calls the “theist on the street” — an everyday believer in God who accepts design based on direct perception or intuition rather than a rigorous design argument. Yet it turns out that his model actually undermines such a person’s design beliefs.

The Model

We summarize his model as follows:

The details of his proposal are manyfold, but the basic idea is straightforward: the locus of design is at the origin of the cosmos (or the laws of nature) (CED, pp. 164–67). God acts at the beginning of the universe, granting to it all that is necessary for biological complexity to eventually unfold. The deity creates the laws of physics and chemistry, which then give rise to preconditions — including “the library of forms” — that enable evolution to produce complex entities. Random mutations and natural selection alone are insufficient for the emergence of biological complexity; preconditions are required, and God ultimately stands behind these preconditions (CED, pp. 97–143).1

So God designed the laws of nature, which then give rise to laws of form and other processes, which eventually produce all flora and fauna. Thus, a person who sees, say, a hummingbird for the first time can rightly intuit (or infer) that it was designed. It’s just that the locus of its design was billions of years earlier and that natural processes transmitted and unfolded this design over time.

The Problem: Part 1

What’s wrong with this picture is that it harms humans’ ability to detect design in the first place. This is for two primary reasons, which build on each other. The first is that it damages a human’s “direct design” beliefs. A “direct design” belief is a belief that a certain type of thing, like a hummingbird, was created by the immediate action of a designer rather than by mediated or secondary causes. As we explain:

In our lived experience, humans readily attribute direct design to various types of biological phenomena. (This is not only true of “theists on the street”, for example, but also of some other people as well.) For example, consider a person who sees a hummingbird for the first time. A natural reaction is to think that this type of bird was directly designed. (“Wow! That’s spectacular. Somebody made that!”) In fact, humans often experience things like hummingbirds as distinct entities — what Axe (2016, pp. 65–86, esp. 71) calls “busy wholes” or what one might call “natural kinds”. That is, humans often experience an entity like a hummingbird as a certain type of thing, and they naturally believe that this type is the result of direct design. By contrast, it is rarely the case that, upon seeing a hummingbird for the first time, a typical person would say, “Wow! That’s specular. Somebody indirectly created that by a process of secondary causes over millions of years”. Instead, many people believe that a designer directly crafted the first instance of a given specimen or feature. (“God made the first hummingbirds, then they reproduced”.) Whether rightly or wrongly, human beings routinely apprehend (or infer) direct design when they encounter the power, beauty, and complexity of organisms or organs.2

So how does Kojonen’s model affect this type of experience? Here’s how:

Yet in Kojonen’s model, these beliefs in direct design are uniformly false. In his view, there is no direct design of biological phenomena. All biological diversity and complexity are the result of indirect design. The locus of design was billions of years prior to the advent of life on Earth. (Indeed, even if Kojonen were to locate direct design at the origin of life, all subsequent flora and fauna would still be the result of indirect design.) This simply follows from Kojonen’s understanding of design (and of evolution). So, if Kojonen’s proposal were true, human beings who accepted his view would have a serious defeater for their ‘direct design’ beliefs about biological organisms and features. They would realize that they have little or no grounds to trust their minds in this context.3

So, in this model, a person would have lots of defeaters for her “direct design” beliefs about biological phenomena. 

But on what basis does Kojonen know that the laws of physics are directly designed? After all, “direct design” beliefs in biology are unreliable and, on his model, biology (alone) has sufficient evidence for design. As we explain:

[H]ow would a person in this general situation know that the laws of physics and chemistry were directlydesigned, as Kojonen believes them to be? Recall that his argument for design is supposed to be based on biological phenomena. But if his model were correct, humans would have no cases of biological things that seemed to be directly designed actually turning out to be directly designed. So, if there are no such cases — and these cases are the basis for believing that the laws of nature are directly designed — then the ground for believing that the laws are directly designed is very poor indeed. If a baseball player strikes out in his first 23 plate appearances, what basis does he have to believe that he will get a hit at his next at-bat?4

The bottom line is that Kojonen undermines his own basis for saying that the laws of physics are directly designed. If so, then he has lost his case for design. The whole point of his model is that biology provides good evidence of design even if evolutionary theory is true. But his view of biology actually undermines his view of design. Whether a person is an expert or an everyday “theist on the street,” anyone who accepts Kojonen’s model can no longer locate design where Kojonen needs it to be.

The Problem: Part 2

 A second problem, building on the first, likewise damages a human’s ability to detect design. A person who accepts Kojonen’s proposal would have significantly less ground for saying that biological phenomena provide evidence of design. This is because his model, to bring about all the flora and fauna in our world, relies on non-agent causessubsequent to the Big Bang. A non-agent cause is any cause that does not include the direct action of an agent. Most non-agent causes are physical in nature. They include, but are not limited to, evolutionary causes. Practically speaking, what does this mean?

For example, if Kojonen’s model were true, a person who accepted the model would believe that, despite her ostensible prima facie belief that, say, a designer directly crafted an eagle’s eye or the first hummingbirds, it is actually the case that each of these phenomena are proximately explained by non-agent causes. For each biological organism or feature, there would be continuity of non-agent causes from before that entity’s existence that led up to (and through) the advent of that entity. Indeed, this continuity would extend all the way back in time. (In fact, there might not be any particular reason, based in biology, to think there was a big bang.) A person who accepted this model would believe that non-agent causes gave (proximate) rise to case after case of biological complexity. The same would be true for human beings, too. An unbroken chain of non-agent causes from the ancient past would extend up to (and through) the rise of the first humans, whoever they happened to be.5

The problem is that “continuity” attenuates (or erases) evidence of design in biology. Given the continuity of non-agent causes to produce all biological phenomena, what basis is there in Kojonen’s model to say that any particular biological entity was designed? Recourse to fine-tuning in astrophysics or the Big Bang in cosmology is no help: the whole point of Kojonen’s model is that biological phenomena point to design. But if every biological entity arose from prior material causes (or non-agent) causes, on what grounds can one say that a mind was needed? Kojonen’s model destroys the detectability of design. There might still be ultimate design (at the beginning of the universe) but the evidence of design — based on biological phenomena — has been obscured.

Arguably, “mainstream” evolutionary theory — which rejects appeals to God in biology — expects strong continuity of natural causes in organic history: there’s no need to invoke God to account for the rise of any particular “kind” because natural causes are held to be sufficient. “Continuity” is just what one would expect if a non-theistic version of evolution were true — namely, that direct design beliefs are uniformly false and that, instead, natural processes appear to be capable of morphing one “kind” into another “kind” over time. Such a view is decidedly unexpected on the pre-theoretic lay theist’s default disposition toward direct design of biological kinds. Mainstream evolutionary theory pushes the theist on the street in precisely the wrong direction. Accordingly, it obscures the detectability of design for such a person. Insofar as Kojonen’s model accepts “mainstream” evolution (as he says it does), his model faces this significant epistemological difficulty.

An Eagle’s Eye

This means that Kojonen’s own biology-based design argument no longer works. After all, such an argument requires that biological design be detectable. If design cannot be detected, it cannot be parlayed into a rigorous argument. This same line of reasoning also undermines the ability of a “theist on the street” to detect design. Insofar as she accepts Kojonen’s model, she would have to regard her initial impression of direct design — of, say, an eagle’s eye — as mistaken. She’d now believe that God didn’t create the first instance directly; instead, it came about by an unbroken chain of material causes (or non-agent causes) throughout the entirety of organic history. For all that she can tell (based on biology), there is no need for recourse to a Mind. Thus, she no longer has grounds to trust her common-sense intuition of the design of the eagle’s eye — or for that matter of any other flora or fauna.     

So much for the design intuitions of everyday theists. For more on Kojonen’s book, see here

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