Douglas Futuyma—Evolutionary Ecology and the Question of Constraints

I have wireless access in the lecture hall today, so I’m going to try liveblogging these talks. This may get choppy! What it will lack in editing will be compensated for by more timely and regular updates. I hope. At least I’ll be able to dump something to the site every 40-60 minutes.

He summarizes the idea that there is a wealth of genetic diversity in populations to allow for effective selection. Lack of mutations should not limit a straightforward selection response. This raises a paradox, however: organisms have phylogenetic niche conservatism. Many species are evolutionarily unadventurous. He works on clades of herbivorous insect species that are sticking to the same plant groups since the Miocene.

May be many niches in nature that are unfilled: example: fish-catching bats have only one species. Where are the nocturnal aerial fish-feeders in other environments? Species don’t just liberally fill every possibility.

Futuyma introduces Gould/Eldredge’s concept of stasis. We need to acknowledge the existence of constraints that are limiting factors on evolutionary possibilities.

Genetic constraints:

In some cases, a “character” doesn’t exist — there aren’t genes or developmental pathways that specify it. For example, thoracic bristle number in flies may not be defined by simple genetic programs. Haldane said humans will not evolve into angels because we lack the required genetic diversity in wings or moral character.

Little or no genetic variance in a character or combination of characters. Looked at Ophraella beetles, asking whether genetic predispositions might limit which species of plants they can feed on. Screened for genetic variation; in about half the cases they found no evidence of genetic variation that would allow for expansion into distantly related plant species. Discussed Bradshaw’s work on genostasis in evolution, which found little genetic variance in heavy metal tolerance in grasses, dessication resistance in rainforest flies, locomotor and life history traits in Hyla. Adaptation observed in some fly species may have been facilitated by hybridization, which introduces the needed variation.

Species evolve along lines of genetic least resistance, where variation is present in the population. Other directions may not be easily followed.

Successful genetic change may require correlated change in multiple other traits, so genetic diversity may hinder evolutionary change by making the optimal combinations rare in the population. Demanding simultaneous changes in larval and adult characters, for instance, might limit rates of change.

Major issue: how much evolutionary novelty is due to new mutations vs. recombination of standing variation in a population?

What accounts for stasis? Most adaptive novelties are associated with shifts to new niches. Because of recombination, new constellations of characters are likely to be ephemeral and not appear in the fossil record — we don’t see them because of issues in population structure. Adaptive gene combinations will be diluted by interbreeding with individuals that lack the combination, so novelties are unlikely to spread very far (unless it’s also associated with reproductive isolation).

During the glacial periods, most species did not adapt to new environments — they used habitat tracking to follow favorable environments. Recombination with more abundant ancestral genotypes leads to collaps of population structures that might favor new forms. Subpopulations lose their character when merged with larger populations, so reproductive isolation is important.

Interesting prediction: ought to be more stasis in times of environmental fluctuation, and more expansion of novelties in subpopulations in times of environmental stability.. Adaptation to rapid environmental change may fail, especially if multiple character changes are required, and extinction is not unllkely. Climate change may simply doom many species. Adaptation to other invasive species is also going to be slow. And many adaptations may be unlikely and evolve only rarely.

Once upon a time, biologists like the idea of convergence — that similar populations might arise in similar environments (I’m thinking of Simon Conway Morris here), but communities are dependent on contingency in evolutionary history, and a deterministic, equilibrial view of ecological “communities” can no longer be supported.

We are seeing a major shift in the discipline to the importance of constraint and evolvability, and the origin of variation. History is important. and there’s increasing integration of disciplines to cover micro- and macro-evolution.

Marc Hauser— where do morals come from? NOT religion.

Whoa. This was a data-rich talk, and my ability to transcribe it was over-whelmed by all the stuff Hauser was tossing out. Unfortunately, I think the talk also suffered from excess and a lack of a good overview of the material. But it was thought-provoking anyway.

One of the themes was how people resolve moral dilemmas. He began with a real world example, the story of an overweight woman in South Africa who insisted on joining a tour exploring a cave, and got stuck in the exit tunnel, trapping 22 people behind her. Do you sacrifice one to save many? One of the trapped people was a diabetic who needed to get out—should they have blown up the woman so the others could escape? This was presented as a kind of philosophical trolley problem, and the audience was asked what was best to do…but I don’t think it works, because unlike those philosophical dilemmas, in the real world we pursue different strategies, and it’s rarely a black and white situation where one has to choose between precisely two possibilities — as in this case, which was resolved by greasing her up with paraffin and pulling her out.

Hauser gave an overview of the philosophical explanations for making moral decisions.

  • Hume: morality intuitive, unconscious, emotional

  • Kant: rational, conscious, justified principles

  • Theist: divine inspiration, explicit within scripture

  • Rawls: intuitive, unconscious, grammar of action: not emotional, built on principles

He’s going to side with Rawls. The key difference between a Rawlsian morality and the others is that a moral decision is made unconsciously, and THEN emotional and rational justifications are made for it. This is testable if you have a way to remove the emotional component of decision; a Rawlsian moral agent will still make the same moral judgments. Studies of brain damaged patients with loss of emotional affect support the idea so far.

He analogized this to linguistics, in which we make abstract, content-free computations to determine, for instance, whether a particular sentence is grammatical. This computation is obligatory and impenetrable; we can’t explain the process of making the decision as we’re doing it, although we can construct rules after the fact.

For instance, he summarized three principles that seem to be general rules in moral judgments.

  • Harm intended as the means to a goal is worse than harm seen as a side-effect.

  • Harm caused by action is morally worse than harm caused by omission.

  • Harm caused by contact is morally worse than equivalent harm caused by non-contact

We don’t judge morality purely on the basis of reasonable outcomes, but also on intent. He suggested that judging only on the basis of whether an outcome is bad or good is a primitive and simplistic strategy, that as people mature they add nuance by considering intentionality — someone who poisons a person accidentally is less morally culpable than someone who does it intentionally.

One example he gave that I found a bit dubious is the use of Transcranial Magnetic Stimulation to shut down regions of brain, in particular the right temporal/parietal junction (which seems to be a locus of intent judgment). In subjects that have that region zapped (a temporary effect!) all that matters is outcome. These studies bother me a bit; I don’t know if I really trust the methodology of TMS, since it may be affecting much more in complex and undefined ways.

Does knowledge ofthe law affect moral judgments? Holland no longer makes a legal distinction betwwen active and passive euthanasia, and many Dutch people are able to articulate a belief that passive euthanasia is less human than active euthanasia. Do the Dutch no longer percieve the action/omission distinction in Hauser’s 3 rules? In a dilemma test, they still make the same distinctions on active and passive stories as others do — actively killing someone to save others is morally worse than simply allowing someone to die by inaction to have the same effect — which again suggests that the underlying mechanisms of making moral decisions are unchanged.

In these same dilemma tests, they’ve correlated outcomes with demographic data. The effects of religion, sex, etc. are negligible on how people make moral decisions.

He makes an important distinction: These are effects on judgment, not behavior. How does behavior connect with judgment?

Hauser describe Mischel’s longitudinal studies of kids given a simple test: they were given a cookie, and told they’d get more if they could hold off on eating it for some unspecified length of time. Kids varied; some had to have that cookie right away, others held off for longer periods of time. The interesting thing about this experiment is that the investigator looked at these same kids as adults 40 years later, and found that restraint in a 3 year old was correlated with greater marital stability, for instance, later in life. The idea is that these kinds of personal/moral capacities are fixed fairly early in people and don’t seem to be affected much by experience or education.

There were some interesting ideas here, and I would have liked to have seen more depth of discussion of individual points. The end of the talk, in particular, was a flurry of data and completely different experiments that weren’t tied in well with the thesis of the talk, and there weren’t opportunities for questions in these evening talks, so it was a bit difficult to sort everything out.

Richard Lewontin—Genetic Determination and Adaptation: Two Bad Metaphors

It was a fine evening here in Chicago, with all these superstars of evolutionary biology in attendance. It was also an information-dense evening — I tried to keep up on my little laptop, but I know I missed a lot. Fortunately, I’m not alone: Rob Mitchum and Jeremy Manier were also covering the event, and have a play-by-play available. I’ll just dump what I’ve got here tonight. I do have wi-fi passwords so I can get things up a little more promptly tomorrow and Saturday.

Richard Lewontin opened up with a few deprecatory comments about the religiosity of our surroundings (the talks were given in a chapel) and our purpose, the reverence given to Saint Darwin. He was there to talk about the importance and danger of metaphors, and addressed two of them. The New Testament metaphor of genes make organisms, and the Old Testament metaphor that organisms adapt to the environment.

It’s not true that genes make organisms. Organisms are consequence of interactions between inside and outside, genes and molecules, and the phenotype is not predictable from the genotype. He discussed the classic example of norms of reaction in Achillea, showing growth of clones in different environments. Cloned plants taken from cuttings — so they’re genetically identical — and grown in different environments show different patterns of growth, and, for instance, don’t show a simple relationship between morphology and the elevation at which they’re grown. Another example is bristle number in Drosophila which show similar unpredictable pattern of response to temperature. Another thing to think about: look at the fingerprints on your left and right index fingers. They’re not identical, but they have the same genes and formed in the same environment at the same time. Living organisms are the outcome of developmental and physiological processes influenced four factors: genes, non-genic molecules in the embryo, environment, and random variation.
Biologists have known this for years but have fallen prey to the metaphor of genetic determinism. (He also mentioned another bad metaphor as an aside: the cell as a machine.)

The other bad bad metaphor is the idea that organisms adapt to ecological niches. Organisms do not fit into preexisting niches. You can’t look at “niches” in the environment…there are an infinity of them. The organism determines the niche. A better idea is the concept of niche construction, in which niches change as organisms evolve. Organisms take whats available and integrate it with their biology, and the life activities of organisms determine what is relevant. When did living in water become the niche of the ancestral seal?

Organisms seek out appropriate environments, the idea of microclimate. Put mesic (adapted to environments with a moderate amount of moisture) and xeric (dry or desert) flies in evironments with different zones of humidity, one surprising result is that the xeric flies move most quickly and determinedly to moist areas, more so than mesic flies. It’s not that dry-adapted flies can handle dryness better…it’s that they’re better at finding damp microenvironments.

Lewontin gave several other examples of organisms that respond in sophisticated ways to confound simple interpretations of adaptation: that we all produce shells of altered microenvironments around us by our metabolic activity; that trees can count the number of days of a certain temperature to trigger flowering; that Daphnia measure the rate of environmental change to determine whether to reproduce sexually or asexually; that organisms modulate the statistical properties of their environment by storage.

He suggested that we need to set aside the bad metaphor of adaptation for a less bad metaphor of construction. Unfortunately, this creates a difficult situation for scientists interested in selection, because, for instance, frequency dependent selection means that the addition of new genotypes to the gene pool (which happens constantly) causes fitness to change in unpredictable ways. It’s a game of rock-paper-scissors with a lot more than just three possibilities. He closed by saying that addressing this kind of problem should be the goal of the next generation of evolutionary biologists.

I ♥ sabbaticals

Why? Because Jerry Coyne can mention this amazing conference, I can take a look at the luminaries speaking at it, and decide at the drop of a hat that I’m going. So this weekend, I’ll be spending my Halloween at a major conference on evolution. Yay!

Look forward to lots of liveblogging (I hope…if they have wi-fi in the conference halls. If not, there will be some massive data dumps in the evenings.)

Physics!

Oh, look. A homeopath explains physics to us all.

I’m sorry. Did I break your brain?

Here’s a non-homeopathic cure. It takes an hour of Lawrence Krauss to counter 8 minutes of that kind of lunacy, I’m afraid.

Yum, genetically engineered plants!

Here’s a good science blog you can help: Biofortified, a group blog on plant genetics and genetic engineering (and, by the way, Sb’s recent addition, Pamela Ronald, is part of the team). They are in a contest to win a small cash grant and an interview with Michael Pollan, and this group is thoroughly deserving — Biofortified is kind of the Panda’s Thumb of plant genetic engineering.

Unfortunately, they’re in second place right now, trailing an anti-genetic engineering, industry sponsored site, and they need more votes to win. You can help out!

To do so, though, is a little more cumbersome than simply clicking on an online poll, I’m sorry to say. You need to register with the contest site, and then click on an entry in an online poll. It’s not too hard, though, especially since Biofortified provides step-by-step instructions. You don’t have much time, with only one day left to vote. Register, then vote for Biofortified!

A happy opportunity to wield our favorite tools

David Sloan Wilson certainly got a warm and appropriate welcome here. His first post was titled Science as a Religion that Worships Truth as its God, a phrase that purées together both “religion” and “science” with “truth” as a wickedly wielded whisk, and immediately set a number of people on edge. Eric Michael Johnson jumped on it, as did Henry Gee (I know he irritated many of the regulars here last time he dropped by, but trust me, sometimes he does say smart things). Gee, in particular, succinctly corrected the title to be “Science as a Religion that Worships Doubt as its God”, which is much better. It’s still a bit confused.

Science isn’t a religion, period. It doesn’t worship anything. Science is a toolbox, and if you must stretch the metaphor even further, doubt is the crowbar we use to get at useful answers…but again, we don’t worship the crowbar. We admire it, can ooh and aaah over a particularly well-tricked-out crowbar, and we can relish opportunities to swing it, but it never, ever assumes the role of religion in our our lives.

David Sloan Wilson is going to fit right in. He’s giving everyone an excuse to swing their crowbars.

Darwinopterus and mosaic, modular evolution

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It’s yet another transitional fossil! Are you tired of them yet?

Darwinopterus modularis is a very pretty fossil of a Jurassic pterosaur, which also reveals some interesting modes of evolution; modes that I daresay are indicative of significant processes in development, although this work is not a developmental study (I wish…having some pterosaur embryos would be exciting). Here it is, one gorgeous animal.

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Figure 2. Holotype ZMNH M8782 (a,b,e) and referred specimen YH-2000 ( f ) of D. modularis gen. et sp. nov.: (a) cranium and mandibles in the right lateral view, cervicals 1-4 in the dorsal view, scale bar 5cm; (b) details of the dentition in the anterior tip of the rostrum, scale bar 2cm; (c) restoration of the skull, scale bar 5cm; (d) restoration of the right pes in the anterior view, scale bar 2 cm; (e) details of the seventh to ninth caudal vertebrae and bony rods that enclose them, scale bar 0.5 cm; ( f ) complete skeleton seen in the ventral aspect, except for skull which is in the right lateral view, scale bar 5 cm. Abbreviations: a, articular; cr, cranial crest; d, dentary; f, frontal; j, jugal; l, lacrimal; ldt, lateral distal tarsal; m, maxilla; mdt, medial distal tarsal; met, metatarsal; n, nasal; naof, nasoantorbital fenestra; p, parietal; pd, pedal digit; pf, prefrontal; pm, premaxilla; po, postorbital; q, quadrate; qj, quadratojugal; sq, squamosal; ti, tibia.

One important general fact you need to understand to grasp the significance of this specimen: Mesozoic flying reptiles are not all alike! There are two broad groups that can be distinguished by some consistent morphological characters.

The pterosaurs are the older of the two groups, appearing in the late Triassic. They tend to have relatively short skulls with several distinct openings, long cervical (neck) ribs, a short metacarpus (like the palm or sole of the foot), a long tail (with some exceptions), and an expanded flight membrane suspended between the hind limbs, called the cruropatagium. They tend to be small to medium-sized.

The pterodactyls are a more derived group that appear in the late Jurassic. Their skulls are long and low, and have a single large opening in front of the eyes, instead of two. Those neck ribs are gone or reduced, they have a long metacarpus and short tails, and they’ve greatly reduced the cruropatagium. Some of the pterodactyls grew to a huge size.

Here’s a snapshot of their distribution in time and phylogenetic relationships. The pterosaurs are in red, and the pterodactyls are in blue.

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Time-calibrated phylogeny showing the temporal range of the main pterosaur clades; basal clades in red, pterodactyloids in blue; known ranges of clades indicated by solid bar, inferred ‘ghost’ range by coloured line; footprint symbols indicate approximate age of principal pterosaur track sites based on Lockley et al. (2008); stratigraphic units and age in millions of years based on Gradstein et al. (2005). 1, Preondactylus; 2, Dimorphodontidae; 3, Anurognathidae; 4, Campylognathoididae; 5, Scaphognathinae; 6, Rham- phorhynchinae; 7, Darwinopterus; 8, Boreopterus; 9, Istiodactylidae; 10, Ornithocheiridae; 11, Pteranodon; 12, Nyctosauridae; 13, Pterodactylus; 14, Cycnorhamphus; 15, Ctenochasmatinae; 16, Gnathosaurinae; 17, Germanodactylus; 18, Dsungaripteridae; 19, Lonchodectes; 20, Tapejaridae; 21, Chaoyangopteridae; 22, Thalassodromidae; 23, Azhdarchidae. Abbreviations: M, Mono- fenestrata; P, Pterodactyloidea; T, Pterosauria; ca, caudal vertebral series; cv, cervical vertebral series; mc, metacarpus; na, nasoantorbital fenestra; r, rib; sk, skull; v, fifth pedal digit.

Darwinopterus is in there, too—it’s the small purple box numbered “7”. You can see from this diagram that it is a pterosaur in a very interesting position, just off the branch that gave rise to the pterodactyls. How it got there is interesting, too: it’s basically a pterosaur body with the head of a pterodactyl. Literally. The authors of this work carried out multiple phylogenetic analyses, and if they left the head out of the data, the computer would spit out the conclusion that this was a pterosaur; if they left the body out and just analyzed the skull, the computer would declare it a pterodactyl.

What does this tell us about evolution in general? That it can be modular. The transitional form between two species isn’t necessarily a simple intermediate between the two in all characters, but may be a mosaic: the anatomy may be a mix of pieces that resemble one species more than the other. In this case, what happened in the evolution of the pterodactyls was that first a pterodactyl-like skull evolved in a pterosaur lineage, and that was successful; later, the proto-pterodactyls added the post-cranial specializations. Not everything happened all at once, but stepwise.

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Schematic restorations of a basal pterosaur (above), Darwinopterus (middle) and a pterodactyloid (below) standardized to the length of the DSV, the arrow indicates direction of evolutionary transformations; modules: skull (red), neck (yellow), body and limbs (monochrome), tail (blue); I, transition phase one; II, transition phase two.

This should be a familiar concept. In pterodactyls, skulls evolved a specialized morphology first, and the body was shaped by evolutionary processes later. We can see a similar principle in operation in the hominid lineage, too, but switched around. We evolved bipedalism first, in species like Ardipithecus and Australopithecus, and the specializations of our skull (to contain that big brain of which we are so proud) came along later.

As I mentioned at the beginning, this is an example of development and evolution in congruence. We do find modularity in developmental process — we have genetic circuits that are expressed in tissue- and region-specific ways in development. We can talk about patterns of gene expression that follow independent programs to build regions of the body, under the control of regional patterning genes like the Hox complex. In that sense, what we see in Darwinopterus is completely unsurprising.

What is interesting, though, is that these modules, which we’re used to seeing within the finer-grained process of development, also retain enough coherence and autonomy to be visible at the level of macroevolutionary change. It caters to my biases that we shouldn’t just pretend that all the details of development are plastic enough to be averaged out, or that the underlying ontogenetic processes will be overwhelmed by the exigencies of environmental factors, like selection. Development matters — it shapes the direction evolution can take.


Lü J, Unwin DM, Jin X, Liu Y, Ji Q (2009) Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proc. R. Soc. B published online 14 October 2009 doi: 10.1098/rspb.2009.1603


I should have mentioned that Darren Naish has a very thorough write-up on Darwinopterus!