A particular version of a genetic trait may have more or less fitness than an alternative version of that trait. Now, imagine a version of that gene that does not function at all. Specifically, it would have less fitness. Or, imagine that the run of the mill protein that helps with implantation works 90 percent of the time, but a new version comes along via mutation by chance that works 98 percent of the time.
That version of the gene would potentially be selected for. It would have higher fitness. So fitness is linked to selection. Something being selected for is something with higher fitness. Usually, it means elimination of the not-as-fit. Most mutations lead to broken, not fitness-enhanced, genetic variance. Natural selection is a creative process that generates or shapes adaptations over evolutionary time. For a trait to be shaped by natural selection it must be genetic and heritable.
For natural selection to affect a trait there must be genetic variation in the population in this trait. This variation must confer differential fitness.
And, other things random effects and selection working away on some other trait must not swamp out the selection. It should be selected against. This post is one of a series on the topic of falsehoods. The following is a list of falsehoods posts in order:. For more about Natural Selection, see this post. The former is merely a test of inequality, the latter is a statement that it equals the exact opposite of something. Wow, Greg. Bob and Dorid: You are both making good points, but missing a key one. I agree with that. That is, in fact, what I say.
Seriously though, this is a good post. There are a lot of maladaptive ideas that come out of this statement, much like initial images conjured up by telling students about light waves. This picture of ocean waves or a guitar string hangs on for a long, long time. I had some issues with a few parts, but overall, it was a pretty nice introduction for most people.
I like the falsehood as teaching tool idea. That is even more false than the one you are dealing with here. Richly historical?
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The man was when he published his last book. He was also very critical of the gene-centered view of evolution, and presented some rather persuasive arguments against it. It quite clearly refers to physical strength or similar to me. In that case, what is a word that describes all these effects combined? Does it? Not perfect you can certainly spot ambiguities , but sufficient for Evolution Elimination is actually what happens.
Remember, mutation arise and then are eliminated, selectivel. Sorry, toto, but this is not vague! Nonrandom elimination is actually perfect. Differential propagation of heritable features caused by their effect on the reproductive success of their bearers. All of the eusocial traits but a few are thus unaccounted for by this theory. That is better than survival of the fittest, but in my view not good enough for I see elimination as the default situation.
Oldcola: I doubt we are disagreeing at all. Most mutations probobaly randomly walk off the edge all on their won fixation, neutral. Selection escorts them to the edge and pushes them off. If you think about it not too long, you either become Larry and simply stop believing that natural selection could do anything, or you start really appreciating hidden variation! Greg Laden: Natural selection is a creative process that generates or shapes adaptations over evolutionary time. Quibbling, that ALSO is a lie.
Survival of the Fittest
Mutation generates the adaptations; natural selection shapes the distribution and sometimes, expression of the generated adaptations. I think there is a general confusion in the commentary here between neutral theory and selection theory. Also, the source of novelty often usually? Alleles are only fit or unfit in relation to other alleles. An unfit allele decreasing in frequency is the same event as a fit allele increasing in frequency. When a novel deleterious mutation gets negatively selected, its alternative alleles are getting positively selected.
The difference is somewhat semantic, though. Biologists have learned a lot about evolution since Darwin published his theory years ago. But nature can still surprise them. The discovery that an ancient merger of microbes opened an unsuspected evolutionary pathway for higher organisms gives biologists a new perspective on earthly life. A new look at million years of marine clam evolution reveals that some closely related clusters of species are more vulnerable to extinction than are life forms generally.
The take away lesson for the rest of us is not to take present scientific knowledge of evolution for granted either in speculating about the development of life on Earth or in environmental planning.
Commenting on discovery of that microbial merger over 2. Those organisms were the cyanobacteria that evolved photosynthesis. It exists more on the Internet than at any one institution. Each is a measurement appropriate to its particular environmental circumstances, a measurement inappropriate for the same or different individuals at different locations or times in the same environment.
One alternative is to allow that the PNS is a necessary truth but continue to hold that it has explanatory content, and can figure in causal explanations of evolutionary outcomes. This is a view advanced by Sober see Sober and examined in Lange and Rosenberg As we shall see in the next section, another possibility is to relativize reproductive rates in favor of another universal measure of fitness. In previous sections, we remarked on the difficulty of identifying the precise propensity that could, according to some, ground fitness ascriptions.
Moreover, it is often difficult to isolate the populations where the evolutionary change is occurring. This is in part an operational problem, but for many biological systems, this difficulty may in fact reveal a deeper ontological issue. Thinking about fitness in reproductive terms depends on the possibility of identifying offspring or successive replicators and populations of them.
For most Metazoans, this appears to be relatively straightforward. But how are we to treat the evolution of colonies, clonal organisms and symbionts and hypothetically ecosystems. Wilson , D. Those boundaries may merely reflect an impoverished way of thinking about biological individuality Pradeu , Haber Many biological individuals are in fact complex arrangements of other individuals.
When these individuals belong to a single species ex. But in the case of multi-species communities e. Moreover, it has been argued Turner , Bouchard , that some individuals that are adapting are not reproducing at all. The difficulties of establishing reproductive success for some clonal organisms, for collectives of organisms and for multi-species assemblages has led some biologists and philosophers to entertain alternative concepts of fitness. Leigh Van Valen, in his attempts to develop a theory of evolution that would allow for the evolution of whole communities Van Valen , , , suggested that fitness as energy control could explain the evolution of a broader range of biological systems.
This has motivated Bouchard , , to argue for an account of evolution focusing on differential persistence reminiscent of Thoday Bouchard , , argues that Persistence Through Time of a lineage is the property maximized by evolution by natural selection: maximization of relative reproductive success or maximization of energy control are only two dominant strategies for persistence increase see Bourrat and Doolittle for related approaches.
Some of the problems of propensities remain, but we gain a way to assess ecological fitness probability of persistence in a way that can be independent of reproductive success. Persistence is the overarching design-problem. The question of how to define biological individuality is an ontological question about what individuals can evolve in response to natural selection. Many biological systems differ in form and in function from our garden variety Metazoans. How are we to understand the evolution of symbiotic communities involving bacteria with lateral gene transfer?
How are we to make sense of the complex traits of eusocial insects? Not all these emergent individuals qua individuals replicate. It is cold philosophical comfort to point out that definitions have to stop somewhere, that the definition of a theoretical term must be distinct from the operational measure of the property it names, and that testability is not a matter of theory meeting data one proposition at a time. In consequence none of these considerations have convinced philosophers of biology to accept the design problem definition, and to give up the project of defining fitness by reference to its effects in reproduction.
Nevertheless, there does appear to be important biological work that the ecological fitness concept can do, and which no definition of fitness in terms of differential reproductive rates—actual, expected, or dispositional—can do. To see what these tasks are, consider the question how do we decide whether a divergence from a long run relative frequency prediction about fitness differences is a matter of drift, a disconfirmation of the hypothesis of natural selection or a reflection of a mismeasurement of fitness differences to begin with? There are four alternatives: a the fitness measure of is right but there was drift—i.
Ignoring the fourth alternative, how do we discriminate among the first three of these? In the absence of information about the initial conditions of the divergence, there is only one way empirically to choose between alternatives a — c. This way requires that there are ecological fitness differences, and that we can detect them. Suppose that fitness differences were matters of probabilistic differential reproductive success no matter what interpretations of probability is adopted.
Then the only access to fitness differences is via population censuses in previous generations since these form the bases of the probabilities. Suppose that this census does indeed show a ratio between as and bs in the recent past. But this is the first step in a regress, since we began with the problem of discriminating drift from mismeasures of fitness. To solve the initial problem, we now have to assure ourselves that the ratios in the past were not the result of drift. Whence the regress.
Of course the problem does not arise if we have access to fitness differences independently of previous population censuses. And this access we have, at least in principle, if fitness is a matter of differences in the solution of identifiable design problems, that is, if there is such a thing as ecological fitness and it is fallibly measured by probabilistic propensities to leave offspring.
Once we have access to ecological fitness differences, we can, at least in principle, decide whether the divergence from predicted long-run relative frequencies, especially where small populations are concerned, is a matter of drift or reflects our ignorance either of ecological fitness differences or the unrepresentativeness of the initial conditions of individual births, deaths, and reproductions. This result also has important implications for the interpretation of the theory of natural selection as a one wholly about populations, and not also about individual fitness differences, discussed above individual versus trait fitness.
Note that the problem of distinguishing drift from selection in ensembles—i. We can distinguish drift from selection in ensembles as well, if we accept that there is such epistemic access to ecological fitness differences and to the initial conditions of births, deaths and reproductions, taken one at a time, and we accept that these individual-differences aggregate into ensemble-differences.
Because populations no matter how large are always finite in size, there is always some drift which needs to be distinguished from fitness differences. Thus even in population biology there is in the end no substitute for ecological fitness and no way to dispense with its services to the theory of natural selection. And since ecological fitness is ultimately a relationship between organisms or individuals taken two at a time, the theory is as much a set of claims about individuals as it is about populations.
This line of reasoning highlights the next phase of the debate. From a discussion about fitness, the debate has evolved into a general debate concerning the nature of natural selection and drift. A number of alternative views have emerged in thinking about these topics. Some e. Others e. Finally others argue that, if it is to play an explanatory role in our theory, fitness has to be an individual and causal concept. The Classical Problem of Fitness 2.
Ecological Fitness 3. Individual versus Trait Fitness 4. The Propensity Interpretation of Fitness 5. Fitness as a Propensity and the Principle of Natural Selection 6. Individual versus Trait Fitness Some philosophers notably Sober, have argued that evolutionary fitness is a property of populations and not of individual organisms, or alternatively that fitness is a property of traits and not of the individuals that possess them.
Fitness as a Propensity and the Principle of Natural Selection The Pence-Ramsey proposal holds out the prospect of dealing with a serious difficulty that long daunted the probabilistic propensity definition of fitness.
How the Problems of Defining Biological Individuality Affect the Notion of Fitness In previous sections, we remarked on the difficulty of identifying the precise propensity that could, according to some, ground fitness ascriptions. Bibliography Ariew, A.
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