Which is the "most evolved" species?

[Mr Skeptic]

A lot of people think we humans are the "pinnacle of evolution", the "highest life form", etc. I blame hubris and also those evolution posters that show a linear progression toward humans. Anyhow, most biologists will typically reply that we're all equally evolved since we've all been around for as long. However, I think that bacteria are the most evolved.

 

First, we need to define "most evolved". There are a few possibilities

1) Most changed from the original life-form.

2) Most acted upon by evolution.

3) Most fit (and how you measure it).

 

The winner for 1) could be found by genetic analysis, and might be the archea. Determining a winner for 3) would be difficult since knowing adaptability would require knowledge of the future. The one I'd go with is 2), since comparing evolution to a genetic algorithm the best result would not be the one that took the longest to calculate, but rather the one with more generations and a more efficient algorithm.

 

We humans have very long life cycles, so that we can do in 15 or so years what bacteria might do in as many minutes, or half a million times faster. On the other hand, we reproduce our DNA 1000 times less accurately, so that we have more mutations (new material). Also, we recombine our genes which as well as helping with adaptability, adds efficiency to the evolution process. For one thing, crossover can occur within a gene potentially forming a new chimeric allele, which has greater than usual odds of being functional. Another way recombination increases efficiency is by allowing the separation of beneficial and deleterious mutations in our genomes. On the other hand, bacteria have high levels of horizontal gene transfer and also plasmids. This horizontal gene transfer makes the whole domain more or less one species. Anyhow, it seems to me that the evolution process in bacteria proceeds the most efficiently, both due to their rapid reproduction and horizontal gene transfer. So given that we have all been around as long, that would make them the most evolved.

 

What do you think?

[Darwinsbulldog]

A difficult thing to answer really. The sheer diversity of life suggests that no one way of living is the perfect one. Do you remain small and generalist, and therefore only do averagely well in times of [relative] environmental stasis, but can have a better chance of surviving a mass extinction---or do you specialize which gives immediate benefits, but may mark you for extinction [again probably] when the shit hits the fan??

[Rip:20]

This is a great topic that is often misunderstood. I'll put my vote in with the bacteria (being a microbiologist), mainly due to the awesomeness of HGT. I want to point out that the Archaea have the shortest branch length (slowest changing), followed by bacteria, with Euks having the longest branches in the ribosomal tree of life. I would also like to say that sometimes evolution works by not changing (purifying selection).

[CharonY]

I belong to those that think that "most evolved" does not make sense. One has to keep in mind that for a long time in our history we all were bacteria. I.e. event that happened to them also happened to us early in our history. None of the proposed criteria are actually useful as for 1) one has to have the ur-genome with which one would have to compare anything that we do not have 2) is outright wrong as evolution does not act on anything, but it is the process during which a defined gene pool changes its composition (i.e. genetic drift, natural selection etc. are the actors) and 3) only makes sense either within a gene pool or ecological niche (i.e. in a direct competitive situation).

[lemur]

I wonder if it would be possible to say that the least "evolved" organisms are actually the most fit. Sharks, for example, are supposedly very similar to the way they were a very long time ago. This is supposedly because they are so well adapted as predators that they have not needed to evolve further. The opposite could also be the case; that species that are evolving rapidly may be headed for genetic instability and thereby extinction. Humans are an interesting case because I have read that medical and other technologies have effectively stopped human genetic evolution, yet some people claim that this allows recessive genes to remain in the gene pool and spread, forming a risk for future expression. I wonder if you couldn't look at it another way, i.e. that by allowing recessive genes to continue several generations by treating their expression, other dominant genes are able to supercede them in meiosis and thereby prevent the loss of dominant genes with recessive genes that occur due to pre-reproductive deaths of individual organisms. In other words, it could be that preventing a recessive genetic characteristic from causing death prior to reproduction maintains greater variation and therefore stability among the dominant gene pool. Remember, no individual organism is devoid of good genes just because they contain a certain amount of bad genes. It's a waste to lose the good with the bad (baby with the bath water), no?

[Darwinsbulldog]

I wonder if it would be possible to say that the least "evolved" organisms are actually the most fit. Sharks, for example, are supposedly very similar to the way they were a very long time ago. This is supposedly because they are so well adapted as predators that they have not needed to evolve further. The opposite could also be the case; that species that are evolving rapidly may be headed for genetic instability and thereby extinction. Humans are an interesting case because I have read that medical and other technologies have effectively stopped human genetic evolution, yet some people claim that this allows recessive genes to remain in the gene pool and spread, forming a risk for future expression. I wonder if you couldn't look at it another way, i.e. that by allowing recessive genes to continue several generations by treating their expression, other dominant genes are able to supercede them in meiosis and thereby prevent the loss of dominant genes with recessive genes that occur due to pre-reproductive deaths of individual organisms. In other words, it could be that preventing a recessive genetic characteristic from causing death prior to reproduction maintains greater variation and therefore stability among the dominant gene pool. Remember, no individual organism is devoid of good genes just because they contain a certain amount of bad genes. It's a waste to lose the good with the bad (baby with the bath water), no?

 

Even the concepts of good and bad genes have problems. What is a bad gene in one environment may be favorable in another. Consider:-

 

"All vertebrates need haemoglobin".

 

This seems to ring true, until you find exceptions. Like ice fish. They can survive without haemo because cold water holds more dissolved gases than warm water. Therefore more oxygen is available to them. Haemo also makes the blood thicker, and this is not a good thing in the cold. So they have evolved anti-freeze proteins as well.

 

Anti=freeze proteins would not do hot springs bacteria much good, and their enzymes only switch on at high temperatures, so for them, and enzyme with a lower temp range would be deleterious.

[lemur]

Even the concepts of good and bad genes have problems. What is a bad gene in one environment may be favorable in another. Consider:-

 

"All vertebrates need haemoglobin".

 

This seems to ring true, until you find exceptions. Like ice fish. They can survive without haemo because cold water holds more dissolved gases than warm water. Therefore more oxygen is available to them. Haemo also makes the blood thicker, and this is not a good thing in the cold. So they have evolved anti-freeze proteins as well.

 

Anti=freeze proteins would not do hot springs bacteria much good, and their enzymes only switch on at high temperatures, so for them, and enzyme with a lower temp range would be deleterious.

That's a good point. However, I think it does even more to support the idea that pre-reproductive death would serve to eliminate genes whose expression could potentially benefit an organism or species at a later time due to environmental changes. I think the most "fit" species/organisms would be those that are capable of the widest range of diversity and flexibility in their adaptations to different climate and resource/feeding situations. So I would still think that a fitter gene pool would be one that loses less genes to natural selection instead of more.

[Darwinsbulldog]

That's a good point. However, I think it does even more to support the idea that pre-reproductive death would serve to eliminate genes whose expression could potentially benefit an organism or species at a later time due to environmental changes. I think the most "fit" species/organisms would be those that are capable of the widest range of diversity and flexibility in their adaptations to different climate and resource/feeding situations. So I would still think that a fitter gene pool would be one that loses less genes to natural selection instead of more.

Yeah, but you still have the problem of the total energy budget for the organism. As a generalist , you can survive in a wider range of conditions, but differential reproduction from more specialized types will squeeze you out of the market. All organisms are selected on the basis of whether or not their "life strategies" work. How much to invest in reproduction, how much to invest in cell repair, immunology, etc, etc. Although there appear to be many "solutions" or to put it another way "life history strategies" , some are more equal than others. Very few large organisms hit on the "perfect strategy" for all seasons. So in a slowly changing environment, the generalist will tend to go extinct before his "u-beaut" "I can survive a catastophy generalist" genes can some into play. Some do, of course.

 

Procaryotes are best at this, without question. Amounst the Metazoa, small is best. Rat-shrew-like things in mammals, most, if not all stem metazoans adaptively radiate after a big extinction event.

[lemur]

Yeah, but you still have the problem of the total energy budget for the organism. As a generalist , you can survive in a wider range of conditions, but differential reproduction from more specialized types will squeeze you out of the market. All organisms are selected on the basis of whether or not their "life strategies" work. How much to invest in reproduction, how much to invest in cell repair, immunology, etc, etc. Although there appear to be many "solutions" or to put it another way "life history strategies" , some are more equal than others. Very few large organisms hit on the "perfect strategy" for all seasons. So in a slowly changing environment, the generalist will tend to go extinct before his "u-beaut" "I can survive a catastophy generalist" genes can some into play. Some do, of course.

 

Procaryotes are best at this, without question. Amounst the Metazoa, small is best. Rat-shrew-like things in mammals, most, if not all stem metazoans adaptively radiate after a big extinction event.

 

This sounds more like an economic analysis of status competition in a meritocracy. By "generalism," do you mean organisms that are somehow more biologically suited to a wider range of climates, foods, predator/pathogen exposure, etc.? If so, why would you assume that a carnivore or herbivore is better capable of finding and consuming food more efficiently than an omnivore? An omnivore might expend less energy on food search and consumption due to the fact that it can consume more calories in a shorter period of time. Anyway, I think your logic is to general and abstract to be really meaningful. You need to give specific examples and reasons to back up your points, I think. You sound like an economist defending division of labor on the basis of theoretical logics of specialization vs. generalism without any attention for detail.

[Darwinsbulldog]

This sounds more like an economic analysis of status competition in a meritocracy. By "generalism," do you mean organisms that are somehow more biologically suited to a wider range of climates, foods, predator/pathogen exposure, etc.? If so, why would you assume that a carnivore or herbivore is better capable of finding and consuming food more efficiently than an omnivore? An omnivore might expend less energy on food search and consumption due to the fact that it can consume more calories in a shorter period of time. Anyway, I think your logic is to general and abstract to be really meaningful. You need to give specific examples and reasons to back up your points, I think. You sound like an economist defending division of labor on the basis of theoretical logics of specialization vs. generalism without any attention for detail.

Not really. The nature of the question is very general in any case...we were talking about general trends. I take your point about my lack of specific examples, but in biology, the exception proves the rule. Carnivores are in the higher trophic levels, and while meat [protein] is energy rich, it's supply is often uncertain. Herbivores, although the supply of food is more certain, contains less calories. Omnivores may be able to access either meat or veg, but they will, in general, be less efficent than carnivores or herbivores. To get better at either, they would have to have their feeding structures etc, modified to be able to better exploit the resource. "Economics" in biology is very relevant. It seems to me tha you have not studied much ecology. Life histories of organisms are very important.

 

Take for example Pacific Salmon. Many species are semelparous. [Have only one reproductive attempt before death] But Atlantic salmon are iteroparous. [More than one reproductive attempt.] Why? You have to look to their environments and their energy budgets.

 

Salmon go back to their birthplace to spawn. In Pacific salmon, the effort of going upstream, jumping up watefalls, against strong currents, etc takes a lot of energy. An animal has only so much energy, some of which has to go to body maintainence, predator avoidence, immunological defence, feeding, reproduction, etc, etc. So a compromise has to be reached. By neglecting maintainece, and putting all it;s effort into one reproductive event because of the effort to get to it's spawning place, the salmon is unlikely to survive after spawning. There is an "opportunity cost" or "trade-offs" to everything. The Atlantic salmon in contrast, faces less of a physical challenge to get to it's spawning grounds, and so can afford to spend a little more on body maintainence so that it can survive several spawning events in it's lifetime. Neither strategy is better than the other in absolute terms, just more relevant to a particular environmental challenge.

 

Over-fishing has caused evolution in commercial fish stocks, driving smaller sizes. Because smaller fish escape though the holes in nets, they survive, so selection pressure will tend to drive them to reproduce when small.

 

So actually, you have it the wrong way round. Economists learn their theory from biologists. And biologists learn it from nature. A few google searches may help you here. eg:-

 

Crespi, B. J. and R. Teo (2002). "Comparative phylogenetic analysis of the evolution of semelparity and life history in salmonid fishes." Evolution 56(5): 1008-1020.

The selective pressures involved in the evolution of semelparity and its associated life-history traits are largely unknown. We used species-level analyses, independent contrasts, and reconstruction of ancestral states to study the evolution of body length, fecundity, egg weight, gonadosomatic index, and parity (semelparity vs. degree of iteroparity) in females of 12 species of salmonid fishes. According to both species-level analysis and independent contrasts analysis, body length was positively correlated with fecundity, egg weight, and gonaosomatic index, and semelparous species exhibited a significantly steeper slope for the regression of egg weight on body length than did iteroparous species. Percent repeat breeding (degree of iteroparity) was negatively correlated with gonadosomatic index using independent contrasts analysis. Semelparous species had significantly larger eggs by species-level analysis, and the egg weight contrast for the branch on which semelparity was inferred to have originated was significantly larger than the other egg weight contrasts, corresponding to a remarkable increase in egg weight, Reconstruction of ancestral states showed that egg weight and body length apparently increased with the origin of semelparity, but fecundity and gonadosomatic index remained more or less constant or decreased. Thus, the strong evolutionary linkages between body size, fecundity, and gonadosomatic index were broken during the transition from iteroparity to semelparity. These findings suggest that long-distance migrations, which increase adult mortality between breeding episodes, may have been necessary for the origin of semelparity in Pacific salmon, but that increased egg weight, leading to increased juvenile survivorship. was crucial in driving the transition. Our analyses support the life-history hypotheses that a lower degree of repeat breeding is linked to higher reproductive investment per breeding episode, and that semelparity evolves under a combination of relatively high juvenile survivorship and relatively low adult survivorship.

 

Unwin, M. J., M. T. Kinnison, et al. (1999). "Exceptions to semelparity: postmaturation survival, morphology, and energetics of male chinook salmon (Oncorhynchus tshawytscha)." Canadian Journal of Fisheries and Aquatic Sciences 56(7): 1172-1181.

Between 2.1 and 6.8% of fall-run male chinook salmon (Oncorhynchus tshawytscha) reared in two New Zealand hatcheries matured as yearling, parr, of similar size to immature siblings. The incidence of mature parr in 58 half-sib families ranged from 0 to 69% of the available males. Although chinook salmon rue normally semelparous, about 80% of mature parr survived to mature again at age 2, and all fish held for another year matured again at age 3. All three ages produced milt that successfully fertilized eggs. Morphological development in mature parr and repeat-maturing males was consistent with that of older, first time maturing males. The gonadosomatic index for mature age-2 males was 11.7, 7.2, and 5.4% for repeat-maturing males, freshwater-reared males, and sea-run males, respectively. Muscle energy density for repeat-maturing males (4.45 kJ/g) was lower than for normal males (5.20-5.45 kJ/g) and negatively correlated with the gonadosomatic index. Although we think it unlikely that repeat maturation occurs regularly in the wild, our results indicate that under favorable conditions, chinook salmon can exhibit some iteroparous traits. We hypothesize an evolutionary continuum between semelparity and iteroparity in salmonids, primarily characterized by modifications in a few key energetic and physiological thresholds.

 

Narum, S. R., D. Hatch, et al. (2008). "Iteroparity in complex mating systems of steelhead Oncorhynchus mykiss (Walbaum)." Journal of Fish Biology 72(1): 45-60.

This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss. Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River = 7.5% and Salmon River = 9.4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18.2%), Imnaha River (17.4%), Pahsimeroi Hatchery (25.2%) and Asotin Creek (22.2%). A lack of correlation between population escapement size and kelt proportions (P > 0.05) suggests that iteroparity was not uniformly expressed across populations, but was significantly negatively correlated with body size (P < 0.05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations. © 2008 The Authors Journal compilation © 2008 The Fisheries Society of the British Isles.

 

Unwin, M. J., M. T. Kinnison, et al. (1999). "Exceptions to semelparity: postmaturation survival, morphology, and energetics of male chinook salmon (Oncorhynchus tshawytscha)." Canadian Journal of Fisheries and Aquatic Sciences 56(7): 1172-1181.

Between 2.1 and 6.8% of fall-run male chinook salmon (Oncorhynchus tshawytscha) reared in two New Zealand hatcheries matured as yearling, parr, of similar size to immature siblings. The incidence of mature parr in 58 half-sib families ranged from 0 to 69% of the available males. Although chinook salmon rue normally semelparous, about 80% of mature parr survived to mature again at age 2, and all fish held for another year matured again at age 3. All three ages produced milt that successfully fertilized eggs. Morphological development in mature parr and repeat-maturing males was consistent with that of older, first time maturing males. The gonadosomatic index for mature age-2 males was 11.7, 7.2, and 5.4% for repeat-maturing males, freshwater-reared males, and sea-run males, respectively. Muscle energy density for repeat-maturing males (4.45 kJ/g) was lower than for normal males (5.20-5.45 kJ/g) and negatively correlated with the gonadosomatic index. Although we think it unlikely that repeat maturation occurs regularly in the wild, our results indicate that under favorable conditions, chinook salmon can exhibit some iteroparous traits. We hypothesize an evolutionary continuum between semelparity and iteroparity in salmonids, primarily characterized by modifications in a few key energetic and physiological thresholds.

 

read some of these papers, and if you take out the species names etc, they do sometimes read like papers in economics.

 

But i have digressed a little, mainly to address your claim that I was thinking as an economist rather than as a biologist. The terms like "predator", "herbivore" and omnivore are too generalist in some ways. Some organisms that are carnivores will sometimes be able to eat plants, and some herbivores can eat meat. Some omnivores tend to eat more meat and less herbivory, and so on. However, an obligate carnivore [herbivore etc] is specialized. I am not denying that bears, which are part of the carnivore family, often eat a lot of plant material. hence the difficulty with examples. Nevertheless, these concepts can be tested. And have been tested. Palaeontologists and biologists have done work on species extinction rates for different groups like carnivores, Herbie, and omnis. By comparing background extinction rates with extinctions in mass extinction periods, we can see clear trends in survivorship in these ecological groups. See studies Stanley and Raup, Simpson, and many others. Generally, "generalist" /omnivores/small species tend to survive mass extinction events, while specialists to be when the environment is more stable. The marine environment is generally more stable than land environments, which is why you see more "living fossils" in sea environments than land. eg coelacanths and Ginkgos on land. There are 'exceptions" of course.

Edited September 11, 2010 by Darwinsbulldog

[lemur]

read some of these papers, and if you take out the species names etc, they do sometimes read like papers in economics.

 

I know they do. Unfortunately, I am the kind of culture-critic who sees similar approaches in various disciplines and questions their general validity instead of assuming that if so many people use them, they must be valid. Although I can understand your logic, it is one of those rules that is geared toward establishing itself as a generalization and who cares about the exceptions. Imo, it does not matter so much whether specialization leads to more efficient energy-economizing because it will never be a law that defies exception. So the issue becomes what explains the success of those species that do thrive by versatility rather than specialization. I have no doubt that many thrive by specialization, but to understand the total logic of evolution, you would have to go beyond specialization, no?

 

Just off the top of my head, I would guess that highly specialized organisms/species would do well in a very stable ecology but fare poorly during periods of evolutionary change. Thus I would expect more versatile species/organisms to survive ecological instability better than very specialized ones. Still, I don't know why such species wouldn't be extinguished during periods of stability if they are in fact out-competed by the more specialized species then.

[Darwinsbulldog]

I know they do. Unfortunately, I am the kind of culture-critic who sees similar approaches in various disciplines and questions their general validity instead of assuming that if so many people use them, they must be valid. Although I can understand your logic, it is one of those rules that is geared toward establishing itself as a generalization and who cares about the exceptions. Imo, it does not matter so much whether specialization leads to more efficient energy-economizing because it will never be a law that defies exception. So the issue becomes what explains the success of those species that do thrive by versatility rather than specialization. I have no doubt that many thrive by specialization, but to understand the total logic of evolution, you would have to go beyond specialization, no?

 

Just off the top of my head, I would guess that highly specialized organisms/species would do well in a very stable ecology but fare poorly during periods of evolutionary change. Thus I would expect more versatile species/organisms to survive ecological instability better than very specialized ones. Still, I don't know why such species wouldn't be extinguished during periods of stability if they are in fact out-competed by the more specialized species then.

Sorry, I was not implying that popularity of opinion is any reliable measure of efficacy, I was just replying to your query about me using 'economic language" in the context of a biological problem. The answer, of course, rests with the evidence as always. One of the difficulties in this sort of general discussion about trends is the contrary data people can point to as evidence for this or that hypothesis. We are nowhere near doing basic descriptions of all the species, never mind detailed studies on the evolutionary history and other biological aspects of those species. Estimates vary on the number of extant and extinct species, so we don't even know how many species are still to be formally described. If different disciplines like [econs and biology] sometimes have convergent views or ideas, and if those views are based on evidence, I have no problem with a hypothesis that may be borrowed from somewhere else.

 

Yes, I was talking about specialization vs generalisation, and generalisation is a sort of specialisation. Natural Selection, Sexual selection, drift -we can talk of many things and use many criteria to try to judge what species are the "most evolved".

[kitkat]

Not really. The nature of the question is very general in any case...we were talking about general trends. I take your point about my lack of specific examples, but in biology, the exception proves the rule. Carnivores are in the higher trophic levels, and while meat [protein] is energy rich, it's supply is often uncertain. Herbivores, although the supply of food is more certain, contains less calories. Omnivores may be able to access either meat or veg, but they will, in general, be less efficent than carnivores or herbivores. To get better at either, they would have to have their feeding structures etc, modified to be able to better exploit the resource. "Economics" in biology is very relevant. It seems to me tha you have not studied much ecology. Life histories of organisms are very important.

 

Take for example Pacific Salmon. Many species are semelparous. [Have only one reproductive attempt before death] But Atlantic salmon are iteroparous. [More than one reproductive attempt.] Why? You have to look to their environments and their energy budgets.

 

 

The story of earth's living biography can be told in so many ways that all have the element of truth. Determining which part they all share is the mystery.

 

Salmon go back to their birthplace to spawn. In Pacific salmon, the effort of going upstream, jumping up watefalls, against strong currents, etc takes a lot of energy. An animal has only so much energy, some of which has to go to body maintainence, predator avoidence, immunological defence, feeding, reproduction, etc, etc. So a compromise has to be reached. By neglecting maintainece, and putting all it;s effort into one reproductive event because of the effort to get to it's spawning place, the salmon is unlikely to survive after spawning. There is an "opportunity cost" or "trade-offs" to everything. The Atlantic salmon in contrast, faces less of a physical challenge to get to it's spawning grounds, and so can afford to spend a little more on body maintainence so that it can survive several spawning events in it's lifetime. Neither strategy is better than the other in absolute terms, just more relevant to a particular environmental challenge.

 

Over-fishing has caused evolution in commercial fish stocks, driving smaller sizes. Because smaller fish escape though the holes in nets, they survive, so selection pressure will tend to drive them to reproduce when small.

 

So actually, you have it the wrong way round. Economists learn their theory from biologists. And biologists learn it from nature. A few google searches may help you here. eg:-

 

Crespi, B. J. and R. Teo (2002). "Comparative phylogenetic analysis of the evolution of semelparity and life history in salmonid fishes." Evolution 56(5): 1008-1020.

The selective pressures involved in the evolution of semelparity and its associated life-history traits are largely unknown. We used species-level analyses, independent contrasts, and reconstruction of ancestral states to study the evolution of body length, fecundity, egg weight, gonadosomatic index, and parity (semelparity vs. degree of iteroparity) in females of 12 species of salmonid fishes. According to both species-level analysis and independent contrasts analysis, body length was positively correlated with fecundity, egg weight, and gonaosomatic index, and semelparous species exhibited a significantly steeper slope for the regression of egg weight on body length than did iteroparous species. Percent repeat breeding (degree of iteroparity) was negatively correlated with gonadosomatic index using independent contrasts analysis. Semelparous species had significantly larger eggs by species-level analysis, and the egg weight contrast for the branch on which semelparity was inferred to have originated was significantly larger than the other egg weight contrasts, corresponding to a remarkable increase in egg weight, Reconstruction of ancestral states showed that egg weight and body length apparently increased with the origin of semelparity, but fecundity and gonadosomatic index remained more or less constant or decreased. Thus, the strong evolutionary linkages between body size, fecundity, and gonadosomatic index were broken during the transition from iteroparity to semelparity. These findings suggest that long-distance migrations, which increase adult mortality between breeding episodes, may have been necessary for the origin of semelparity in Pacific salmon, but that increased egg weight, leading to increased juvenile survivorship. was crucial in driving the transition. Our analyses support the life-history hypotheses that a lower degree of repeat breeding is linked to higher reproductive investment per breeding episode, and that semelparity evolves under a combination of relatively high juvenile survivorship and relatively low adult survivorship.

 

Unwin, M. J., M. T. Kinnison, et al. (1999). "Exceptions to semelparity: postmaturation survival, morphology, and energetics of male chinook salmon (Oncorhynchus tshawytscha)." Canadian Journal of Fisheries and Aquatic Sciences 56(7): 1172-1181.

Between 2.1 and 6.8% of fall-run male chinook salmon (Oncorhynchus tshawytscha) reared in two New Zealand hatcheries matured as yearling, parr, of similar size to immature siblings. The incidence of mature parr in 58 half-sib families ranged from 0 to 69% of the available males. Although chinook salmon rue normally semelparous, about 80% of mature parr survived to mature again at age 2, and all fish held for another year matured again at age 3. All three ages produced milt that successfully fertilized eggs. Morphological development in mature parr and repeat-maturing males was consistent with that of older, first time maturing males. The gonadosomatic index for mature age-2 males was 11.7, 7.2, and 5.4% for repeat-maturing males, freshwater-reared males, and sea-run males, respectively. Muscle energy density for repeat-maturing males (4.45 kJ/g) was lower than for normal males (5.20-5.45 kJ/g) and negatively correlated with the gonadosomatic index. Although we think it unlikely that repeat maturation occurs regularly in the wild, our results indicate that under favorable conditions, chinook salmon can exhibit some iteroparous traits. We hypothesize an evolutionary continuum between semelparity and iteroparity in salmonids, primarily characterized by modifications in a few key energetic and physiological thresholds.

 

Narum, S. R., D. Hatch, et al. (2008). "Iteroparity in complex mating systems of steelhead Oncorhynchus mykiss (Walbaum)." Journal of Fish Biology 72(1): 45-60.

This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss. Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River = 7.5% and Salmon River = 9.4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18.2%), Imnaha River (17.4%), Pahsimeroi Hatchery (25.2%) and Asotin Creek (22.2%). A lack of correlation between population escapement size and kelt proportions (P > 0.05) suggests that iteroparity was not uniformly expressed across populations, but was significantly negatively correlated with body size (P < 0.05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations. © 2008 The Authors Journal compilation © 2008 The Fisheries Society of the British Isles.

 

Unwin, M. J., M. T. Kinnison, et al. (1999). "Exceptions to semelparity: postmaturation survival, morphology, and energetics of male chinook salmon (Oncorhynchus tshawytscha)." Canadian Journal of Fisheries and Aquatic Sciences 56(7): 1172-1181.

Between 2.1 and 6.8% of fall-run male chinook salmon (Oncorhynchus tshawytscha) reared in two New Zealand hatcheries matured as yearling, parr, of similar size to immature siblings. The incidence of mature parr in 58 half-sib families ranged from 0 to 69% of the available males. Although chinook salmon rue normally semelparous, about 80% of mature parr survived to mature again at age 2, and all fish held for another year matured again at age 3. All three ages produced milt that successfully fertilized eggs. Morphological development in mature parr and repeat-maturing males was consistent with that of older, first time maturing males. The gonadosomatic index for mature age-2 males was 11.7, 7.2, and 5.4% for repeat-maturing males, freshwater-reared males, and sea-run males, respectively. Muscle energy density for repeat-maturing males (4.45 kJ/g) was lower than for normal males (5.20-5.45 kJ/g) and negatively correlated with the gonadosomatic index. Although we think it unlikely that repeat maturation occurs regularly in the wild, our results indicate that under favorable conditions, chinook salmon can exhibit some iteroparous traits. We hypothesize an evolutionary continuum between semelparity and iteroparity in salmonids, primarily characterized by modifications in a few key energetic and physiological thresholds.

 

read some of these papers, and if you take out the species names etc, they do sometimes read like papers in economics.

 

But i have digressed a little, mainly to address your claim that I was thinking as an economist rather than as a biologist. The terms like "predator", "herbivore" and omnivore are too generalist in some ways. Some organisms that are carnivores will sometimes be able to eat plants, and some herbivores can eat meat. Some omnivores tend to eat more meat and less herbivory, and so on. However, an obligate carnivore [herbivore etc] is specialized. I am not denying that bears, which are part of the carnivore family, often eat a lot of plant material. hence the difficulty with examples. Nevertheless, these concepts can be tested. And have been tested. Palaeontologists and biologists have done work on species extinction rates for different groups like carnivores, Herbie, and omnis. By comparing background extinction rates with extinctions in mass extinction periods, we can see clear trends in survivorship in these ecological groups. See studies Stanley and Raup, Simpson, and many others. Generally, "generalist" /omnivores/small species tend to survive mass extinction events, while specialists to be when the environment is more stable. The marine environment is generally more stable than land environments, which is why you see more "living fossils" in sea environments than land. eg coelacanths and Ginkgos on land. There are 'exceptions" of course.

[Genecks]

Well, I got into an argument with a professor who got his Ph.D in Evolution and Ecology about this issue a little. A few months ago, I think. I basically claimed that birds could be an example of the pinnacle of evolution, of which he replied that there is no pinnacle of evolution. I wanted to say in reply, "Well, if sh** gets too complicated, they can just fly away." But I held that part in. Humans can't easily "fly away."

 

Fair enough, but I think you could still look at this from different angles:

 

I could see the following as pinnacles of evolution:

1) Bacteria: Have the ability to reproduce and evolve and have remained on Earth a long time. Then again, in terms of an individual species, they often change or mix and evolve, etc. etc..

2) Birds: Their cognitive skills and small body exemplify how the body to brain mass ration downsized until a species can remain cognitive, intelligent, and yet keep a bout of survival. It's really their memory and cognitive skills that make me think their brains underwent amazing amounts of evolution. They have impressive memory skills.

3) Humans: Humans are impressive in that they can examine, feel, and discuss the nature of the universe and how they may have come about existence. More importantly, they are the first species to really accomplish this feat and devise technological ways to seek answers to their questions.

 

What makes the birds and humans different is that they have a brain. Furthermore, they have a sense of existence and the natural world around them. They can bend the situation. Birds, unlike apes, can simply fly away if things get too complicated.

 

Perhaps the angle is best described this way:

 

Take a biological structure/function, examine which species has wielded it the best, and attribute the pinnacle of evolution of that attribute to that species.

 

In a lot of ways, when we think of the pinnacle of evolution, there is a concept similar to the Great chain of being, for which there is a path of moving "up."

Edited September 14, 2010 by Genecks

[Darwinsbulldog]

I think that evolution has "direction" and "purpose" without implying any teleological or metaphysical woo to those words. "Direction" is the sense that fitness, born of natural selection, can avoid extinction. {for a time}. And "purpose" is the sense that species tend to fill niches opportunistically, but of course, gaps occur. NS is both aided by, and in opposition to, drift. It is the ability of evolution [by totally natural means] is able to fill what Daniel Dennett calls 'design space" by using cranes like sex to give the illusion of intent.

 

Further, we know [with hindsight] evolution was able to produce [at least once] beings with mind who can create and innovate from living material that could create and innovate without mind. And that this material arose out of chemical evolution...the presence of a self-replicating object that copied itself sloppily enough to allow mistakes and thus variation, and so move from chemical evolution to the biological.

 

The philosophical impact of this is profound. Life can pull itself up by it's own bootstraps and create mind. Within a mere four billion years. A mind that can then peer back to it's chemical origins. All this without woo. No divine knob-twiddler is required. Merely some local matter-energy gradients. We may never know all the detail of how it all happened. But we do not need to invoke Kenneth B. Miller's "god-of-the-quantum-gaps", nor Ayala's "Knob twiddling, switch-pulling god who kick-started evolution god". Just brute facts and good theory. That is the true "magic" of our existence.