Our earth is populated with all kinds of bizarre animals. Should we assume that almost all of their features are (or had until recently been) adaptive, in other words, necessary for their survival or that of their offspring? That does not seem very likely. One source of non-adaptive features may be co-evolution of sexual preferences of male and female specimen of a species, becoming increasingly bizarre. As a consequence one or both of the sexes may develop features that are awkward in other respects than sexual attraction. An obvious example of this are the antlers of male elks, which have become monstrous because the female elks prefer such a male. At first, perhaps, because big antlers signify male vigor and health, but this co-evolution of sexual preferences may get out of hand if the environment were not challenging enough for the survival chances in other respects during a prolonged period. The elk can still afford to have such antlers, but circumstances may change for the worse.
Next to sexual selection, animal characteristics may change as a consequence of mutations that may continue to exist as long as rivals, predators, scarcity of food and other necessities of life do not punish them.
My conclusion is: the evolutionary principle of survival of the fittest is only operative during trying times. In periods and niches during which surviving is relatively easy, another principle is operative: survival of the not evidently non-fitted. Perhaps we should call it the principle of evolutionary stagnation.
Or to be more precise: an environment is never challenging in all respects at the same time, so in that respect it is not very trying, and bizarre animal features may develop that persist for a long period until the environment changes and these features will no longer be immune from extinction.
Peter,
Survival of the fittest sums up Darwin's theory and is based on three principles:
1- There must be diversity on a trait (what you call feature)
2- The trait must be under selective pressure
3- The trait must be inheritable
You are right that the selective pressure depends on the environment and there is no reason to consider it as stable in time. When selection pressure gets lighter, the trait tends towards neutrality.
However, you cannot consider that individuals with the previously selected trait can become stably non-fitted in a new environment. Indeed, non-fitted means reduced fitness and since the conditions 1 and 2 are still valid, the trait should be counter-selected.
Survival of the fittest is any case a misnomer - and is better expressed as survival of the most reproductively successful. That can be either in terms of numbers, each with a low level of parental investment (r strategy - fish etc) or quality, where each offspring obtains a high level of parental investment from one or two parents and perhaps even relatives (k strategy - humans, elephants etc).
Natural selection influences whether the individual survives in their environment whilst sexual selection influences whether they get to reproduce. Within this there is intra- and inter- sexual selection. Some signals, such as the peacocks tail, or deer's antlers have the potential to become runaway if only sexual selection was in operation but this can be prevented from happening by natural selection - i.e. when the feature the opposite sex finds attractive becomes exaggerated to the point where it reduces the carriers chances of surviving long enough to get the chance to mate.
It also goes without saying that when environments change or animals move into different environments different selection pressures come into play and this is a pressure for animals to change. Sexual selection has to follow the pressures of natural selection under these circumstances as adaptations that the opposite sex find repulsive or unattractive could not develop. This is also where the point Philippe makes about diversity comes into play as this allows some variations to be favoured over others and to be expressed with increasing frequency in subsequent generations. The classic example of this are to the two forms of the salt and pepper moth (Biston betularia), that have different survival rates depending on environmental conditions
Thank you both for your explanations. I agree in principle. But what I wanted to stress is that some selective pressures of different kinds may be mild or absent for a prolonged period, and during such a period it seems better to speak of survival (better: non-extinction) of the not-evidently non-fit. Intra- and especially intra-sexual pressures may promote the selection of animal characteristics that become increasingly bizarre but do not endanger survival and reproduction for the time being. Of course, in the long run maladaptive features will disappear again. But at any period there will always be animals with some awkward characteristics that are not yet put under selective pressure. During that period, in that respect, there is evolutionary stagnation or even degeneration, and it seems more accurate to see it as ruled by the principle of "non-extinction of the not-evidently non-fit".
Shortly after I posted this topic I came across the point of view of Mayr (2004) who states we had better think in terms of "elimination of the inferior individuals" instead of "selection of the superior individuals". This leaves, he argues, much more room for sexual selection going astray and accidental events in the evolution, thereby offering a better explanation for the unpredictable, capricious course of the evolution and the enormous variation in species than the principle of selection of the best individuals is offering.
Mayr, E. (2004). What makes biology unique? Considerations on the autonomy of a scientific discipline. Cambridge: Cambridge University Press.
The Adaptationist program was thoughtfully criticized by Gould and Lewontin in their famous 1979 paper. I think many of the questions here are well discussed in this paper :
Gould, S. J., & Lewontin, R. C. (1979). The Spandrel of San Marco and the panglossian paradigm: a critique of adaptationist programme. Proc. R. Soc. Lond. B, 205, 581–598.
http://rspb.royalsocietypublishing.org/content/205/1161/581.full.pdf+html
Gould and Lewontin's analogy of the spandrels supporting the San Marco in Venice - being a by-product of architectural constraints, instead of an adaptation directly promoted by the evolution - is not very convincing as far as I can judge it. See the criticism by Dennett (Darwin's dangerous idea, 1995, p. 271), nicely summarized by Tadeusz Zawidzki (2007): Dennett. Even if it were sound, I don't think it has a strong relation with what I am trying to explain here.
Thank you Maggie, for such a reference. Old wine in new bottles holds for many proposals in science pretending to say something original. However, the point of view you are referring to may profit from substitituting explicitly the slogan "survival of the fittest" by "non-extinction of the not-evidently non-fit". It makes in one glance clear what is different in both views. Perhaps the authors used this phrase, but, then, it did not become famous.
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