The strong perennial vision: a response

Timothy Crews and Lee DeHaan (henceforth, C&D) of the Land Institute have written the above-titled paper1 in response to my paper ‘The strong perennial vision: a critical review’2, which I’ve discussed in my previous two blog posts. As mentioned in those posts, C&D provide this threefold characterisation of my argument:

  1. Ecological theory suggests that perennial grains may yield less than annual grains
  2. Strong criticisms of annual agriculture are unfounded, both socially and ecologically
  3. Focus on perennial grains detracts from more important strategies for achieving agricultural sustainability

The first of these points is much the most important, and that’s what I’m going to focus on in this post.

C&D versus CSR

C&D’s main gambit is to suggest that Grime’s CSR theory (described in my previous post) is a general framework for understanding plants in their habitats, which becomes misleading when it’s applied in the manner I use it to specific plants, particularly plants under artificial selection. There’s some force to the first part of this objection. There’s continuous variability of plants across multiple traits, not complete segregation into C, S or R types. And, certainly, there is no cast iron law of ecological logic that demands augmentation of one trait must inevitably lead to the diminishment of another. So possibly it’s true that I use the CSR framework in too general a way, and that I interpret tradeoffs too stringently.

But though the CSR framework is indeed a generalising one, Grime himself and me in my usage of his framework do focus on two specifics: resource availability and disturbance. By contrast, C&D in their discussion of ‘stress tolerance’ invoke it in a very much more general sense to mean anything that stresses the plant. Then they go on to have some fun at my expense by using the framework very specifically in order to identify various complexities of stress tolerant, ruderal and competitive traits that transcend the annual-perennial divide, and of the existence of high resource (but non-seedy) herbaceous perennial systems.

In my view, it’s best not to fixate on ‘perenniality’ as such but instead to examine the covariance of traits like longevity, sexual allocation etc. So I’m not sure how much of C&D’s discussion here is relevant to my arguments, and I’m not sure how much they and other Land Institute authors really understand the relationship between resource availability, disturbance and sexual allocation. But yes I concede that there’s plasticity of plant traits with which plant breeders can work. How much? In C&D’s opinion, a lot: whereas I posit a tradeoff between augmenting stress-tolerant traits (low resource input, individual survival) and sexual allocation, they profess “no experimental evidence [of this] to our knowledge”.

So in C&D’s view, the CSR framework goes out the window and plant breeders have a free hand to work with the unique traits of given plant species which, through artificial selection, they can work up into whatever phenotypes they want. CSR theory, in this view, “does not address what happens if humans were to create a new type of habitat never before seen in nature”. The kind of habitat they have in mind, their ‘domestic prairie’ of perennial grains, is one that “requires the development of a never seen in nature environment with high resource availability, little tillage, and with strict human directed selection for maximum seed yield over several years”. C&D criticise me for misconstruing domestic prairie as something requiring little or no human inputs or management, and for being too hidebound in my thinking about feasible agroecosystems by the habitats that are actually found in nature. Instead, they invoke the authority of Professor Ford Denison who argues that “humans will likely have the greatest success in breeding for traits that were never previously selected for in nature”.

Of selection, natural and artificial

Let me try to work through some of this. First, it’s noteworthy to learn – despite all of Wes Jackson’s writings on ‘natural systems agriculture’ and the mimicking of natural ecosystems – that C&D’s programme turns out to depend on an absolute break with natural ecosystems more thorough than that of extant agricultures, and indeed unprecedented in the history of agriculture to date. That doesn’t necessarily mean it’s a bad idea or that it won’t work, but I think those permaculturists who enthuse about perennial grain crops as an example of nature mimicry might sit up and take note. Still, with Denison’s work as inspiration, C&D pursue a line of argument that’s certainly plausible: unaided by human hand, natural selection won’t necessarily find solutions that work well in agriculture for human purposes.

But let me pursue an alternative, more permaculture-oriented and nature-mimetic argument than C&D, with Denison once again acting as my guide. Perhaps natural selection hasn’t come up with seedy herbaceous perennials because such plants involve fundamental tradeoffs or contradictions which artificial selection will be unable to surmount any better than natural selection. Denison certainly thinks so – his book Darwinian Agriculture3 has a chapter called “What won’t work: misguided mimicry of natural ecosystems”. Its premier example is the Land Institute’s perennial grain breeding programme.

So it seems to me a little cheeky for C&A to invoke Denison in support of their programme. It’s true that Denison argues for the merits of breeding for traits not previously selected for in nature, but the sort of examples he uses (like short-strawed cereal varieties) are more consistent with my emphasis on pushing plants in directions they’re already predisposed to go in evolutionarily than in a contradictory push to increase both sexual allocation and individual survival.

If it’s true that through careful selection of plant traits crop breeders can overcome the basic biological tradeoffs encountered by wild plants, then C&D may be right that Grime’s framework is irrelevant here, that there are no fundamental obstacles to producing high-yielding, endogenous nutrient-cycling perennial grain crops, and that these plants will not be subject to existing ecological constraints. But I don’t think it is true. I take the point that there’s underlying plasticity and complexity of traits amongst plants that isn’t captured in a simple framework like CSR. In ecology these days, life history seems to trump r/K or CSR. Citing Barbour et al4, C&D state “There are as many life history patterns as there are species…” Perhaps. There is always a scientific tradeoff between generalisation and particularisation. C&D try to have it both ways by invoking CSR theory in a very general way to refute the specifics of my analysis and in a very specific way to refute the generalities of my analysis. But to infer that there is no higher level ecological patterning of life history involves the mistake of not seeing the wood for the trees in an almost literal sense.

In his early work Grime adduced the CSR framework in relation to detailed studies of English grassland plants. In his more recent work, he’s applied it to the whole of the biota throughout the history of life on earth – whence his statement that the outcomes of natural selection are restricted “to a rather narrow range of basic alternatives in life-history, resource allocation and physiology”5. These are what Grime calls the ‘evolutionary strategies that shape ecosystems’, which are applicable to past, present and, one must assume, future ecosystems.

I’m not sure on what grounds C&D think the plants they breed can escape these evolutionary constraints simply by virtue of the fact that they have been artificially selected. That’s not the case with the current suite of artificially selected annual crop plants, which bear all the traces of those constraints ordained by natural selection – hence the whole problem of annual tillage agriculture. To me, C&D’s position greatly overstates the autonomy from Grime’s ‘narrow range of basic alternatives’ that can be achieved by artificial plant breeding. Sure, we can push the envelope with things like fertiliser and pesticide laced short-lived orchard trees propped up on sticks on dwarfing rootstocks. In their paper, C&D make quite a play against my view that the example of high input/output apple orchards isn’t a sensible prototype for a sustainable perennial agriculture and involves a hypostatisation of perenniality per se. But to my mind, the example of the intensive orchard exemplifies precisely the tradeoff problems associated with issues like survival, longevity, nutrient response and agroecosystem management that I explore in my paper in detail and that C&D ignore almost entirely in their response.

C&D say that there’s no experimental evidence for the tradeoff I posit between sexual allocation and perennial-type survival traits. Grime’s framework provides an experimentally-validated evolutionary and ecological context, while Peggy Wagoner’s 1990 review6, supplemented by various more recent studies I cite, is a veritable litany of artificially-bred perennial grain varieties that either survived well and produced little seed, or produced a lot of seed and survived poorly. In a blog post7, Land Institute breeder David Van Tassel explicitly acknowledges that perennial grains will be subject to various tradeoffs, and in my paper I explore the biological basis of these in detail – an analysis again ignored by C&D in their response.

The most compelling evidence C&D invoke to refute my suggestion of a sexual allocation–survival or longevity tradeoff is a study of sunflowers in which ‘early successional perennials’ had a higher sexual allocation than annuals. Well, nature is never quite as orderly as our models of it, but I can’t say I find a slight anomaly of this sort across longevity or R-C-S trends hugely undermining of my basic argument, and as I’ve already said CSR may be a better way of thinking about the issues than annual vs perennial. I’d like to know how long-lived the high-allocating early successional sunflowers were, their survival rate, whether they exceeded annual allocations in every year of their lives, and whether the studies controlled for allometry. Unfortunately, I’m unable to access the relevant paper, but its abstract states “A number of studies have tested whether reproductive effort (RE) is correlated with successional maturity; in these, annuals generally had higher RE than herbaceous perennials (29 and 13%) and RE in herbs often diminished as succession progressed”8. On the face of it, this looks to me more confirmatory of my arguments than of C&D’s.

Probably the best experimental evidence for the difficulty of breeding perennial grains that can match the yields of annuals is the fact that nobody has managed to do it in at least 10,000 years of extraordinary agricultural achievement, and in over 100 years of professional, scientific plant breeding. Land Institute authors have written a paper that explains with some degree of plausibility why the first farmers were unlikely to have domesticated perennial grain crops9, but if the problem is mostly just a matter of coming up with the right set of traits to work with, the historic, global failure to have found them anywhere in the world at any time since seems to me quite a troubling issue for their line of argument. More plausible, I think, to accept Peggy Wagoner’s view: “the resources available for seed production in a perennial appear to be less than in an annual”6.

Domestic Prairie

C&D describe the ‘domestic prairie’ that the Land Institute is working to develop as a “never seen in nature environment with high resource availability, little tillage, and with strict human directed selection for maximum seed yield over several years”, and they think I misconstrue the concept as something more natural and less interventionist.

Perhaps I am muddled about domestic prairie. I do find it a rather elusive concept. According to Wes Jackson it’s “based on nature’s ecosystems” and has something to do with “natural systems”10; according to C&D it’s that never-seen-in-nature environment and a high resource input agroecosystem where they “hope that as much as possible these resources can come from nutrient cycling and endogenous sources”; and according to Jackson and other Land Institute authors it’s something that’s going to end 10,000 years of conflict between agriculture and nature. Most annual grain farmers surely hope that “as much as possible” their nutrient inputs can come from endogenous sources too. How much is C&D’s “as much as possible” and what yields will be associated with it? The answer to that question is surely critical, but C&D don’t address it; instead, they studiously ignore my paper’s analysis of nutrient response, and invoke the misleading example of non-starchy and non-seedy forage and perennial biofuel crops.

At what point does ‘domestic prairie’ segue into ‘green desert’? When does ‘natural systems agriculture’ become plain old anthropogenesis? Would a polyculture of Roundup Ready® alfalfa and corn be domestic prairie? And how exactly is all of this going to end the conflict between agriculture and nature? In a recent post I criticised Mark Shepherd’s emphasis on nature mimicry in his ‘restoration agriculture’ project for its protean character, and I think the same is true of C&A’s domestic prairie. Basically these systems (probably all systems) mimic nature except where they don’t, and the concept of ‘nature mimicry’ then becomes essentially rhetorical.

The discussions around both perennial grain domestic prairie and Roundup Ready® domestic prairie seem to me to overstate the extent to which agricultural problems are reducible to plant breeding problems. In both cases, it’s as if agricultural problems can be solved purely or largely by genetic manipulation of plant traits without any messy ecology getting in the way out in the field. In the case of Roundup Ready® corn, that conceit is already belied by the emergence of Roundup tolerant weeds. With perennial grains, I think there will be different but no less daunting problems. These essentially revolve around the very narrow parameters involved in juggling high sexual allocation in a protein or carbohydrate rich seed crop with high perennation year after year, funded only out of longer-season photosynthesis, through the vicissitudes of weather and climate to produce agriculturally acceptable outputs within the ebb and flow of complex plant guilds, with no or at least ‘little’ (the distinction is probably quite significant) herbicides, pesticides, fertilisers or tillage despite their high resource demands. Before anyone starts talking about ending 10,000 years of conflict between agriculture and nature, I’d like to see some sound numbers put to those parameters.

Conclusion

I accept that there’s plasticity with which plant breeders can work, and if somebody could explain to me what domestic prairie really is I could probably be persuaded that it’s possible to develop a domestic prairie of decently yielding and decently long-lived perennial grains, though probably not as high yielding as annuals. In fact, I already accepted this possibility in my paper. But I’m not convinced that C&D and the Land Institute adequately emphasise the extremely tight parameters within which such a domestic prairie would have to operate and the tradeoffs it would have to reconcile if it’s to found a high-yielding low environmental impact grain agriculture long-term. And, as I’ll explain in my next post, I’m not sure a high yielding grain agriculture is such a great idea in any case.

References

1. Crews, T. and DeHaan, L. 2015. ‘The strong perennial vision: a response’ Agriculture and Sustainable Food Systems, 39: 500-515.

2. Smaje, C. 2015. ‘The strong perennial vision: a critical review’ Agriculture and Sustainable Food Systems, 39: 471-99.

3. Denison, F. Darwinian Agriculture, Princeton University Press.

4. Barbour, M. et al. 1987. Terrestrial Plant Ecology. Benjamin/Cummins.

5. Grime, J. and Pierce, S. 2012. The Evolutionary Strategies That Shape Ecosystems. Wiley-Blackwell.

6. Wagoner, P. 1990. Perennial grain development – past efforts and potential for the future. Critical Reviews in Plant Sciences 9: 381-408.

7. Van Tassel, D. 2012. Tradeoff or payoff? http://perennialgrainresearch.blogspot.co.uk/2012/11/biomass-accumulation-by-miscanthus-in.html

8. Hancock, J. and Pritts, M. 1987. Does reproductive effort vary across different life forms and seral environments? Bulletin of the Torrey Botanical Club 114, 1: 53-59.

9. Van Tassel, D., DeHaan, L., and Cox, T. 2010. Missing domesticated plant forms: can artificial selection fill the gap? Evolutionary Applications 3: 434-52.

10. Jackson, W. 2002. Natural systems agriculture: a truly radical alternative. Agriculture, Ecosystems and Environment. 88: 111-117

14 thoughts on “The strong perennial vision: a response

  1. Again – a masterful offering. And I feel like the poor bloke running to catch a train that’s already left the station as I try to keep up with all you’ve put up the last couple days.

    I am going to give it the ‘ol college try’ to parse the entire set of offerings as this subject intersects some of my own work. But before I can manage all of that I will break in here to point out a possible hiccup in your “best experimental evidence for the difficulty… [it hasn’t been done]”… Simply put – who is paying to do this? The current model for all the professional, scientific plant breeding we witness today is overwhelmingly underwritten by seed company entrepreneurs who actually have a vested interest in NOT breeding perennial plants. These entrepreneurs recoup their investments selling seed. If you only sell seed once, well, you’re a smart guy. Now – just because this is how its being done today doesn’t mean this is how it has to be done forever more. And it is only in my own lifetime the commercial plant breeding enterprise has eclipsed the public enterprise (universities and government funded efforts) that did once manage to do most plant breeding. To be quite transparent this eclipsing of efforts is most obvious for the major broad acre (and annual) crop species – there still remain many public breeding efforts for crops with smaller economic footprints. But I hope to make two points with this revelation. First, the fact that it hasn’t been done in 10,000 years (or more to the point in roughly 80 years of very scientific plant breeding) of effort doesn’t immediately lead to the conclusion it can’t be done. And second, the paltry budget available to the Land Institute to do the work they’ve laid out for themselves makes me wonder if its not their ecological or plant breeding knowledge to be held suspect, but the financial realities in front of them that make them seem like dreamers.

    Oh, this should not be taken as evidence I think they’ll succeed. In large measure I think you’re on the winning side of the specific argument here. And because the odds of making perennial crops into winners seem quite long indeed I imagine the effort comparable to putting men on the moon and bringing them back alive. We did manage that, but it wasn’t cheap.

    • Thanks again for that Clem – more interesting points. Agreed there’s a conflict of interest with private seed companies…some of the mid 20th century efforts were undertaken in the Soviet Union, however, so no problems of that sort there… and as you say, the commercial takeover is quite a recent thing… I guess I’d want to argue that the fact that nobody’s developed a high-yielding perennial grain agriculture through history (despite developing all sorts of other fancy tricks with perennials) is a bit of prima facie evidence for its difficulty, though of course you’re right that ‘not done before’ isn’t the same as ‘can’t be done’. Maybe one interesting question is the parallels between natural selection and artificial selection through time – can we say that, barring future technological leaps, emergent patterns of artificial selection have manifested through time? The implications of the Land Institute paper (ref 9 above) is that there were good reasons why the first farmers didn’t go for perennial grains, and so after that nobody else much bothered with it for the next 10,000 years. Doesn’t seem that persuasive to me. I suspect humanity lucked out with the cereals and one or two other staple crops, and there are few other places for us to go in crop development terms.

      • I’m not an expert on domestication biology… or said another way, I’ve read enough on the subject to realize far more has been studied on the subject than I’ve had a chance to digest. But I have a feeling that dumb luck may have played a significant role (so yes, your suspicion that humanity lucked out seems fair from this end). Luck or no, the biology of annual plants does make them more amenable to manipulation than perennials. Low hanging fruit if you will (though interestingly the ‘low hanging fruit analogy’ draws on perennials such as apple).

        One issue I have with Ford Dennison’s argument that nature has had the time to test virtually every conceivable genetic combination is the matter of context. There are situations now that may favor gene combinations once tested by nature and discarded (or passed over) as not an improvement. Further, as humanity discovers other means of controlling the environment(s) around our domesticates there can be gene combinations that would have been unfavorable in the wild but are more than acceptable under husbanded conditions. Add to this the vast expanse over which some of our domesticates are deployed and even very small changes in performance can translate into significant improvements in yield or some other character.

        You ask: “…can we say that, barring future technological leaps, emergent patterns of artificial selection have manifested through time?” And I’ll confess I’m not certain I take your exact meaning, but I can offer that even in the minute passage of my professional career (minute on a geological scale) there have been changes in breeding objectives that make germplasm once prized for its excellence just another relic of a time gone by. Technology has allowed significant improvement in our ability to do our work, and further discovery of biological principles have enabled us to better design experiments, and interpret the results we witness. Increased population pressures do weigh on our consciousness, but increased populations also increase demand for food and in a capitalist scenario this is an added opportunity. From all this one can easily paint a metaphor of a technology treadmill. And if this is all the farther one wants to look then dismal horizons can be brought up. But so long as more food can be teased from the resources at hand it buys time for socially inclined folk to tease out solutions to other issues humanity creates for itself.

        Another possible avenue for the perennial breeders to pursue may actually be more a task for food scientists… and that would be to use plant parts (say rhizomes for instance) that could be harvested without too much detriment to the plant and figure ways to transform these materials to foods (fermentation is one thought). This route may have the benefit of using the perennial plant’s natural tendencies – obviating the need to completely reprogram their survival strategies. But its late and this notion might look pretty dull in the light of day.

  2. Oops, wanted to add that I’ve not yet looked at ref #9, and need to remedy that. But I also seem to recall there was a ref you saw an abstract of but couldn’t get the paper for. I’ll see if I have the means to remedy that as well.

    • Thanks Clem – caught up just now with lambing, onion planting & broccoli selling but I’ll come back to this soon.

      • On a completely unrelated topic to the post: is it typical to schedule lambing for this late in the season? Our lambing is typically in January. Is the goal to have the mothers out on spring grass?

        • Well I’m a novice shepherd but yep, that’s pretty much it. Here, as I understand it people generally lamb Dec/Jan for the Easter market or else in April to coordinate with the grass. Just finished my first ever lambing with all of two ewes – now with four lambs. Pretty magical. Now…back to perennials…!

  3. So to pick up your comments Clem – I’m interested in your food science idea…has the cold light of day yet dampened it? My only comment would be that ‘fermented rhizome surprise’ would have to taste darned good to incentivise its production, or else you’d need to get some good advertisers on board.

    On the breeding side of things, I take your point about the possibilities for new crops or combinations. Again, it may be a matter of levels and contexts. I’m sure that things have moved on and there are all sorts of new cultivars on the block but I suppose the point I take from people like Grime and Ford is that at a somewhat more overarching level the basic ecological niches aren’t much different, and that puts a question mark over perennial grain crops. If Crews & DeHaan could offer some compelling counter-evidence then maybe I’d be persuaded, but a blanket dismissal of CSR’s relevance, an enthusiasm for intensive orcharding and the example of early successional perennial sunflowers doesn’t cut it for me.

    Bear in mind that as well as arguing for perennial yields equivalent to annual ones, the aspiration is to do so with endogenous inputs and other conservation-type entailments…though when pressed C&A’s ‘domestic prairie’ reverts to a highly managed and high input ecosystem. Either way, it’s an incredibly demanding set of parameters that they’re claiming to deliver – and I don’t yet see their grounds for claiming to end any 10,000 year conflicts…

  4. “Fermented rhizome surprise” indeed. We may have just found a great advertiser to bring on board!!

    In the glaring light of a new day (and an extra night to sleep on it) the notion of using other parts of perennials for new food uses still has some merit for me. But before I head off trying to embellish the ad necessary to build such a sale I might first offer that it’s just as easy to shoot down the concept. Why bother then? Nothing ventured…

    New foods are difficult. I’m not a food scientist, but as a food grade soy person I do get to talk to food folks often and have learned quite a bit from them. I should perhaps drop back a second and remind that I grew up on a small farm and got the opportunity to grow what we ate. We grew a lot of different things and I ate the same. Can eat almost anything (known to be edible); and have noticed that when hungry the will to try something new is enhanced. But my experience is not so common. I’m told there are lots of folks who are quite risk averse in terms of what they’re willing to eat. Perhaps ‘comfort food’ is as much psychological as anything. But it’s also worth pointing out we are not down to our last bean – so the hungry incentive hasn’t kicked in either.

    Globalization may be modifying this a little, at least in some circles. Trying various international cuisines may be gaining steam and I imagine this a good thing. The difficulty to our present ‘make food with what you’ve got’ idea is it may run aground of the ‘no none else has ever done this’ complaint. I guess what I’m saying is you’ll likely have more luck getting someone to try taro root or cassava before ‘fermented rhizome surprise’… just because someone else has already demonstrated you can eat it and survive.

    All in all however I imagine the value of looking at the world from various different perspectives is much greater than the cost. A concept like ‘fermented rhizome’ (I think we want to lose the surprise part 🙂 ) may get lost on the cutting room floor, but having allowed it to simmer with all our other ideas it might someday find its resurrection alongside other notions which make it seem more useful. Perhaps like making sausage, or a good stew.

    In the second paragraph of this last comment you return to Grime and Ford, and though I agree there are some broad swipes in ecological realities there still remains some wiggle room. And most of the plant breeding I’ve worked with has made hay in the realm of this wiggle room. But aside from my own personal experience – if one wants to witness just how large a space might be inhabited by all this so called ‘wiggling’ then you can hardly do better than to consider the Illinois Long Term Selection experiment on corn done by Lambert and others. If their results don’t suggest to you that plant breeding can take account of ecological realities and still turn what we have into something more akin to what we want, then I suppose I’ll have to try more ‘out of the box’ thinking to make my case.

    On the last paragraph – I agree the perennial crop advocates have suggested a super ambitious goal. But like fermented rhizomes… nothing ventured, nothing gained.

    • I’ll have to take a look at the Illinois experiment. Wiggle room sounds about the right phrase overall – but I think the Land Institute program involves more than what you could justifiably call ‘wiggle room’. Agreed though, nothing ventured… I’m not arguing that they shouldn’t be doing what they’re doing or that they won’t produce something useful (a lower yielding but perennial grain would certainly be useful…) However, I’m not persuaded by their arguments as to why perennials suffer no yield penalty relative to annuals, or by their hyperbolic comments about ending the conflict between agriculture and nature, which I think has unfortunate consequences of various kinds…

  5. Will await your assessment of wiggle room. I hope I’m granted a tiny wiggle room when you come back to the nutrition discussion of a pulse + cereal diet’s value. Ascorbic acid and the history of Limeys might get tossed in my face. I’ve checked and can be confident vitamin A won’t bruise my argument, so now I’m on the lookout for sufficient vitamin C. Would it hurt an aspiring pulse to nick a tomato now and then?

    If your goal (concerning the claims made by the Land Institute scientists) is to disabuse them of their argument there is a conflict between nature and agriculture then I would suggest moving the landscape of the conflict somewhat. The real abuse of nature for me is not so much agriculture in general, but how it is practiced in particular. Agriculture in a sense is practiced by ants; and they really have no natural argument against these little guys. Wasteful activities (over watering, over spraying, over tilling) these are things to be avoided. Indeed you’ve made the point (and properly I think) that the perennial agriculture they’re describing will still require much managing… and the managing is where improper practice can occur.

    Now where did I leave my tomato seedlings?

    • Yep, much to agree with there – your general/particular and ants points are interesting, and lead into the kind of analysis of prairie agriculture undertaken by the likes of Geoff Cunfer nicely … but I’ll have to come back to that another time.

  6. I love being cited by both sides of an argument and don’t see anything wrong with citing someone you agree with on some points, even if you disagree on others. But I haven’t quite said “humans will likely have the greatest success in breeding for traits that were never previously selected for in nature”. I’ve said that traits that never existed before have not been “rejected by past natural selection” (in contrast to things like increasing the expression of existing genes) and so they *may* not always come with tradeoffs. But I don’t think it will usually be possible to create such radically new traits through conventional breeding. For conventional breeders, the best options will often involve reversing past natural selection, either to take advantage of conditions that didn’t exist in the past (as Clem suggests) or in cases where tradeoffs rejected by natural selection are acceptable to us. The best-known examples are dwarf wheat and rice (less competitive with weeds, but with greater yield potential), but I discuss many more in my book. I’ve made some additional comments on Chris’s paper on my Darwinian Agriculture blog, which I have to move to another server before the end of June.

  7. Thanks Ford – you’re right of course that there’s no reason C&D shouldn’t cite you in relation to where they’re in agreement, albeit that your refinement of their paraphrase would seem to make your position less complementary to theirs. I guess I was just a bit disappointed that their approach largely seemed to involve seeking short cuts for dismissing my analysis out of hand, rather than taking it a bit more seriously. Your uncertainty about the ease of overcoming CSR type tradeoffs interests me – this is probably the most critical point in judging the merits of the two analyses.

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