Helping others at no cost to oneself is generosity, but altruism implies sacrifice, yes? We can happily disagree on that - I was merely pointing that it is a very clear and usable definition (from Sober/Wilson) and addresses all the criticisms raised by sceptical biologists.
^^^^ CB: Yes, I agree to your definition. The word is not an important issue. ( What's in a word ? smiles) The important thing is that you have defined it clearly for purposes of discussion. Some unselfish behavior is "alttruistic" and some is "generous".
^^^^^
> CB: I gotta go , but I don't think differentiation between individuals
> comes out of the fitness struggle.
I know we are speaking colloquially, but it is worth noting explicitly that the struggle for survival itself does not produce traits (in the classical model; newer more speculative research seems to suggest development pathways that might be triggered or guided by external conditions, but I won’t get into that here to avoid muddying matters further). Traits i.e., the underlying genetic mutations, occur at random (within constraints imposed by molecular biology/chemistry).
^^^^^ CB; I agree. And this is a very important point. Traits that come out of "the struggle for survival" of a parent generation would be LaMarckian, and the synthesis includes the dogma of no inheritance of acquired characteristics or an anti-LaMarckian principle. That is, a living organism doesn't t in its struggle for existence modify its gonads to create a trait in its daughter organisms that responds to improve the daughter's fitness in her similar struggle for existence. New traits result from random mutation. Random meaning they are random relative to the life struggles and tasks of the parent organism. The random mutation gives rise to traits that are selected for in the struggle for survival of the daughter generation ( see my last post from overnight on "survival" referring primarily to the survival of breeds or species , not the survival of individuals).
I see below in your summary and reference to Maynard Smith you opt for class ,not individual , fitness.
^^^^^
The vast majority are maladaptive - they decrease the fitness of the individual and are typically wiped out because they cause the individual to be wiped out before s/he can reproduce to pass it on. The ones that happen to have - entirely by chance - a fitness advantage lead to an individual with a slightly differentiated genetic makeup (of course we all have different genetic makeup already and those are fitness neutral or negligible).
^^^^^ CB: Agree completely
^^^^^
Genetic variations - which manifest as phenotypic variation - occurs within/between individuals. I assume you agree with that part. With that in hand...
^^^^ CB: Yes, though see my post critiquing the notion of "indvidual fitness".
^^^^^
> The result of a "fitness" struggle
> between individuals would be one individual survives to reproduce and
> the other individual doesn't. That wouldn't result in differentiated
> individuals co-existing and going on to become sexually incompatible.
> It would lead to only one individual and offspring continuing to
> exist. In Darwin's model, it is whole species that go extinct.
> Becoming sexually incompatible arises from geographic separation of
> populations, not some "fitness" struggle between individuals.
Species extinction is a somewhat separate matter: it occurs because species exhaust their resources, are unable to adapt to a changing environment (or adapt out of their current form), suffer catastrophic environment collapse (e.g: K-T extinction) or lose the evolutionary arms race to a predator.
^^^^ CB: Well, yes, but in biology species extinction or survival, or breed extinction or survival is _the_ matter of concern. The "fitness" comparison of two individuals only matters to the extent that one individual contributes offspring to the survival of the species or breed and the other does not. In the phrase , "survival of the fittest" , it is not really individual survival ( or extinction) that is meant. There really isn't individual "extinction". There can be individual death without producing offspring or producing fewer offspring than some other individual. But all individuals die and don't "survive" in the natural historical time scale.
^^^
In fact, what you write in the first two sentences above, taken together, is roughly what is posited by Darwin’s theory (and continued in the New Synthesis). We left off in the earlier section on a hopeful note of agreement that new traits emerge in individuals as a result of random genetic variation. Assuming that hope is justified i.e., you agree with that:
^^^^^ CB: I do
^^^^^
a small number of these traits have a selective advantage: they stretch one (or a few) giraffe’s neck a bit longer, they make one gazelle run a bit faster, or in trickier cases when present as a recessive allele in red blood cells they provide resistance to malaria. The “fitter” individuals (the ones with these new traits) have greater reproductive success and leave more offspring sporting their traits. They in turn reproduce at a higher rate, so on … these multiple variations coexist for a [possibly indefinite] period. This is the evolution of a species based on fitness measured by natural selection.
^^^^^ CB: Yes, see my post from overnight. It's just that "immediately" in the transgenerational sense, this fitness becomes a group or breed fitness. Agreed that a random mutation improving fitness is most likely to occur in just one individual ( I think; not 100% sure of that). But it's immediate affect is that that individual has several offspring with the new trait. And the new trait explodes exponentially in succeeding generations. That's because the most critical measure of fitness is differential fertility, i.e. greater fitness means that a trait causes or allows reproduction of more offspring. Differential mortality ( the measure of fitness of the three examples you give above) acts indirectly by allowing differential or greater fertility. An individual or breed living longer is only more fit if in the course of the longer lives more offspring are produced. Differential fertility is the bottom-line of fitness.
^^^^^
On sexual incompatibility or speciation, as you note geographic separation/isolation and similar factors can produce a split i.e., cladogenesis. I agree with that point. What I meant - stated poorly (by mixing a particular kind of speciation - anagenesis - with fitness/selection) - was that this is not a matter of or evidence for *selection* occurring at the species level (see previous paragraph).
^^^^^ CB: Yes cladogenesis first can produce new breeds , groups of the same species, still able to interbreed and produce viable, fertile offspring, but with different traits of some type. Eventually, if some trait arises in one of the breeds that prevents inter-breeding between the separated populations, there is speciatation, no ? Now should have said yesterday, that the two species - one old ,one new - can "survive". But sometimes one goes extinct. That would be selection growing out of cladogenesis. But I agree that not all selection occurs like this. See the dinosaur example in my overnight post.
^^^^^
To see why speciation does not give evidence for selection/fitness across species, consider the case of geographic or other isolation leading to the formation of a new species. Why is it that species X1 and species X2, now separated over generations, are unable to interbreed? It is because they are too dissimilar in their genetic signature. But they had the same signature when they cohabited as species X. What caused their genetic makeup to differentiate and fixate?
In summation, natural selection for fitness, in the classical/standard model, addresses the question of how and why traits arise within species, not how species compete against each other (*). In other words: species are the unit of evolution but individuals are (in the traditional/accepted case) the unit of selection (*).
—ravi
^^^^ CB; Yes , I think we agree. However, I would say that the moment at which the new traits arise in an individual is extremely fleeting and really premature for measuring its _fitness_. If a new trait only _stays_ in an individual, does not "immediately" spread to make a new breed, i.e. group, not individual, then it is almost by definition not a more fit trait. A population of one or small population is very vulnerable to "extinction"; very vulnerable not to survive for very many generations. A fit trait must go beyond an individual or it is not fit, so why speak of individual fitness ?
^^^^^^^
(*) This is not to say that species do not compete for the same resources or that they do not prey on each other. In that sense, they are part of the “natural” selectors that influence the traits that are selected in the target species. Powerful lions and leopards are part of the environment that “selects” faster gazelles. But it is the gazelles that have evolved a “faster” phenotype that survive, and ultimately reproduce more and up the top speed of gazelles.
^^^^^ CB: Yes, but it is important to focus on differential fertility primarily and differential mortality secondarily. Traits that make gazelles directly more successful at fertile matings are more powerfully fit than traits that allow gazelles to escape predators. I only say this because the original Darwinian discussions are dominated by the differential mortality factor ( in the famous poem "red in tooth and claw" , the red being blood and death). Darwin's reference to "struggle for existence" tends this way too, though the effort to have sex can be a struggle.
It comes up here in the long term thread over whether humans still have heterosexual instinct. Lack of heterosexual instinct in species that reproduce sexually would be about the most unfit characteristic possible for an individual, breed or species. That's why I think it must still exist in most humans. The trait of heterosexual instinct is a qualitative level above all other traits as necessary for the fitness of a sexually reproducing species. A random mutation that vacated heterosexual instinct would "go extinct" very fast in competition with individuals/breeds with a heterosexual instinct. I'm not saying it can't be suppressed by humans. But I don't think it could have been obliterated with humans relying solely on socially determined or culturally generated heterosexuality.
^^^^^^^^
Of course this is a simplification:
1. Summarising Maynard Smith, fitness is not a property of an individual but of a class of individuals - the class in which the new phenotype/trait is expressed.
^^^^ CB: There you go. That was my original statement. I don't subscribe to the idea of fitness of individuals. Fitness is not a property of an individual, but of a class or breed. Smith was a Marxist, by the way.
^^^^^
2. Phenotypes coexist with others, and it is the totality of these expressed in a class of individuals that is subjected to test by natural selection.
^^^^ CB: Yes, the class can be a breed or a species. For example many species and higher phyla and taxa were selected against in the dinosaur mass extinction and other mass extinctions. In the dinosaur mass extinction, certain mammal species were more fit than the dinosaur species. That was species fitness.
^^^^^
3. Fitness can certainly be measured at any group level: genes are coded in pairs of alleles. A trait that decreases reproductive success of the individual in whom it is *expressed* might still provide a species-level benefit since the trait might be suicidal to the individual when expressed in a few individuals but beneficial to the rest of the group/species in whom it is present only as a recessive allele.
^^^^^^^ CB: By the way, one of my teachers in anthropology was the late Professor Livingstone famous for the study on heterozygous for the sickle cell gene, which is more fit in malaria environment than homozygous for lack of the gene, when homozygous for the gene is suicidal for an individual. This is breed , not species fitness. That is, as you imply, the group level here is breed not whole species.
^^^^
One example might be Wilson/Sober’s brain worm, a parasite that lives inside ants and attempts to modify the behaviour of the ants so that the ants are consumed by cattle (in whose gut the worms want to end up). They achieve this behaviour modification in an amazing way: one “altruistic” individual burrows his way up into the host ant’s brain and “rewires” (there’s that word again) it to attain the desired behaviour. His/her work done, this individual perishes in the brain of the ant, giving up his/her life for the benefit of the rest, who carry this suicidal trait in as a recessive allele, to be passed on to a select few in expressed form in future generations.
^^^^^ CB: Interesting. Altruistic, self-sacrificing, indeed. So, the altruistic ant is homozygous for the gene and the beneficiaries are heterozygous ?
Thanks for this discussion. I've been waiting to think this all the way through clearly again.