It's dangerously easy to say "oh yea, makes sense, natural selection happens by mating so if mates choose club wings, I get it. Obvious." But Prum's trying to go a step further, and test just how far out of balance and arbitrary the mate selection part can be from the direct do-not-die part of evolutionary fitness.
He proposes that we can differentiate between these two by considering that the club wings aren't actually indicators of higher direct fitness, because they hurt the ability to fly, even among females that have no need for such shenanagins. I'm not sure I totally agree with or grasp that, but at least it's an attempt to further understand and test the idea.
I'm frankly surprised by comments accusing a well established evolutionary biologist of severely misunderstanding natural selection. The author has spent his career, among other things, investigating mechanisms of evolution, and identifying and performing tests to assess their relative importance to a particular species (here's an example: http://prumlab.yale.edu/sites/default/files/prum_1997_phylog...).
You might consider whether your objections are addressed in his work not aimed at the lay population, and that your criticism really just amounts to "He wrote this at not exactly the right level of sophistication for me." Maybe that's true, but it's a pretty boring claim.
Some traits are shaped by sexual selection because of their deleterious effects. It's an honest signal: if you can survive despite having that crappy trait, you must be really robust!
You can't conceptualize that as a fitness hit, because of what fitness means in the context of evolutionary biology. But you had better be able to conceptualize it somehow, because it's interesting and important if true.
species die out because of maladaptive pressures. that doesn't contradict the theory of evolution and natural selection's role in it.
If we said 40 millions years ago - protowhales cannot run as fast because their mates really like the membranes between their legs this would still be technically true.
Most birds can fly because their parents could fly. The genes for flying stick around because so many other traits of birds have evolved to benefit or rely on the ability to fly. But that doesn't mean flying itself is some magical end goal. Flying is only useful for natural selection insasmuch as it grants the organism a better likelihood of reproducing.
Why would natural selection necessarily prefer birds that are ideally designed for flying in what we perceive as a graceful manner? In fact, we know that it doesn't. Ostriches, emus, and penguins can't fly, though their ancestors were able to. That is not evidence that they are evolutionary dead ends. The huge variety of penguin species that have evolved since the ancestor of penguins lost the ability to fly proves the opposite, in fact.
This bird clearly flies well enough to continue to survive. If the traits that work against it flying gracefully grant it more reproductive success than flying slightly better would, then natural selection will favor those traits.
Natural selection is often treated far too preciously. Sure, it took a genius in Darwin to identify and clearly describe the phenomenon, but the process itself is tautological. It comes down to, "the things that reproduce better reproduce better". This bird exists, therefore natural selection favored its traits. If we don't understand why, the failure is ours, not natural selection.
The author of this article is an Evolutionary Biology researcher at Yale. It would be really weird if he severely misunderstood natural selection.
Yes, Virginia, "most biologists," who get their news from Nature and Cell, are sadly lagging behind laypeople who read the New York Times. Is it any wonder people have so little faith in scientists? I think science journalists have a responsibility to highlight the fallibility of scientists and the flaws of the scientific process, but it is not public-minded criticism to make your readers believe that the majority of scientists working in an area are too dense to understand something that an average person can understand from a newspaper article, or already did understand if they read a single pop science book about evolution in the last several decades. That's just pandering.
Now, we could make the same mistake and assume that we, who do not write science journalism, have noticed something about it that one of its most successful practitioners (published in the New York Times, after all) never has. Or we could assume he understands it better than we do and does this shit on purpose because he likes being published.
Sexual selection definitely produces some interesting effects, but it's still a form of natural selection. This article portrays it as the opposite. I think it's far easier to understand the outcomes of sexual selection if you realize that reproductive success is the only thing that matters. And the factors that influence reproductive success vary widely. It's important to not get eaten, die of disease, starve to death, or die young. But for organisms that reproduce sexually, it's even more important to be able to find a mate. An organism that lives twice as long but reproduces just once is far less successful than an organism that lives half as long but reproduces twenty times. The whole idea that sexual selection is somehow at odds with natural selection instead of just being one of many selection pressures, is deeply confused.
Well, I can't say concerning Ostriches etc but a common pattern in recently emerged islands is for birds to reach the island first. There not being any predators, some of the bird species evolve to being flightless. Once rats or other mammals reach these Islands, these species tend to become extinct. So naturally occurring "evolutionary dead-ends" are certainly possible (European sailors releasing rats and rabbits to the many islands they visited accelerated the process but it is still "inevitable" since mammals will to a given Island sooner or later).
Sure, one can define selection and fitness "internally" and thus whatever survives is "fittest" up to a given point. But it seems reasonable to take an external view and judge that certain evolution paths lead to the end of species. There's no reason abolish this kind of analysis just because one has honed the specific, technical meaning of these terms so that they aren't concerned with the question.
I believe most of the time you're right, the changes are random. However, at least one experiment has shown that species can pass adaptive traits to their offspring (called Lamarckian inheritance) [1]. The experiment is intriguing, in that it seems to hint something more is going on than the Darwinian inheritance model.
[1] http://newsroom.cumc.columbia.edu/blog/2014/07/17/effects-of...
It's Aristotelian biology.
After all, no real visible phenotype is truly based on a single gene, but rather the dynamic interplay of hundreds of gene products over the course of the organism's development.
Yes.
> evolution selects at multiple levels
That's just another way of saying that evolution selects for reproductive fitness with respect to a particular environment. If a gene is part of an organism, then the other genes in that organism are part of that gene's environment.
The aggregation of genes into organisms is itself an evolutionary adaptation (as is the aggregation of organisms into more complex organisms like eukaryotic cells and multi-cellular creatures). This aggregation provides reproductive fitness by enforcing a certain level of cooperation among the aggregated genes (see https://en.wikipedia.org/wiki/The_Evolution_of_Cooperation). But this is not the fundamental mechanism of evolution, and every now an then a gene "defects" and does what is best for it at the time. Cancer is an example of this.
Naively expecting "better" organisms to win fails to explain why these birds are evolving progressively "worse".
But if you go down and look at genes which handicap the male while triggering some silly attractiveness glitch in females versus genes that don't, it becomes clear that as long as the handicap isn't too strong, the former genes may easily win.
I think that's a point for the GCVOE this time.
It's my understanding that gene-centered view is the main view among evolutionary biologists.
Multi-level adaptation seems to have fallen under lack of evidence. Evidence from nature, mathematical theory, and evolutionary simulations seem to back up selfish gene theory. There are still people like David Sloan Wilson who work on it.
TFA has a weird definition for natural selection.
Evolution has no preferences and sexual selection is natural selection.
It's a matter of definition, I think. Darwin made a distinction between natural selection and sexual selection,
> Sexual selection was first proposed by Charles Darwin in The Origin of Species (1859) and developed in The Descent of Man and Selection in Relation to Sex (1871), as he felt that natural selection alone was unable to account for certain types of non-survival adaptations. https://en.wikipedia.org/wiki/Sexual_selection
So the distinction the article here makes is a reasonable one with a long history. But more recently, the terms are often defined as non-distinct,
> Factors that affect reproductive success are also important, including sexual selection (now often included in natural selection) https://en.wikipedia.org/wiki/Natural_selection
Traits need to be considered with the ones they compete against. It's impossible to judge the bird in isolation.
Since the 1930s, it's been well known that in some cases sexual selection will undermine natural selection. Very simply, if a male is liked by most females, then a female has an incentive to mate with that male, even if the female does not like that male, because then her male children will have a trait that most females like. This can lead to a feedback loop that then goes to far, with maladaptive consequences.
This is a well studied case:
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Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of exaggerated male ornamentation by persistent, directional female choice. An example is the colourful and elaborate peacock plumage compared to the relatively subdued peahen plumage; the costly ornaments, notably the bird's extremely long tail, appear to be incompatible with natural selection. Fisherian runaway can be postulated to include sexually dimorphic phenotypic traits such as behaviour expressed by either sex. Extreme and apparently maladaptive sexual dimorphism represented a paradox for evolutionary biologists from Charles Darwin's time up to the modern evolutionary synthesis. Darwin attempted to resolve the paradox by assuming genetic bases for both the preference and the ornament, and supposed an "aesthetic sense" in higher animals, leading to powerful selection of both characteristics in subsequent generations. Fisher developed the theory further by assuming genetic correlation between the preference and the ornament, that initially the ornament signalled greater potential fitness (the likelihood of leaving more descendants), so preference for the ornament had a selective advantage. Subsequently, if strong enough, female preference for exaggerated ornamentation in mate selection could be enough to undermine natural selection even when the ornament has become non-adaptive.[3] Over subsequent generations this could lead to runaway selection by positive feedback, and the speed with which the trait and the preference increase could (until counter-selection interferes) increase exponentially ("geometrically").
Doesn't change the fact that preferring those traits are ingrained in us due to thousands of years of evolution and aren't changing any time soon. Worry about what you have control over you'll be happier
This species is doomed by the chasing of this superficial attractiveness.
> ...the evolutionary mechanism behind this novelty is not adaptation by natural selection, in which only those who survive pass on their genes, allowing the species to become better adapted to its environment over time. Rather, it is sexual selection by mate choice...
In natural selection, it is only individuals which mate which pass on their genes -- surviving is no good if you don't mate! It is my understanding that sexual selection has been classed as a variety of natural selection. If the species sexually selects itself to a point of maladaption, it goes extinct -- just as if it was maladapted to its environment for any other reason. Notably, these birds are not there: they still seem to be okay.
> In the absence of direct costs to the choosers, the population will not be saved by natural selection. Because the cost is deferred, the whole population can ease further and further into maladaptive dysfunction, generation by generation.
This seems to be treating natural selection as a game of one round, or describing a situation where there is almost no capacity for variation in the species. But if it's really true, that the species is in a kind of dead-end, where the most successful mates are the most maladapted, and there is little capacity in the genome to remedy this situation -- as the females could develop a different standard of attraction, or the males some other method of attraction -- then the effect of natural selection would be to extinguish the species. This is, in some sense, how "progress" is made in natural selection -- as much by elimination as anything else. This leads us to:
> Instead of ensuring that organisms are on an inexorable path to self-improvement, mate choice can drive a species into what I call maladaptive decadence...
It has been said by many more well informed than I am, that there is something specious about an "inexorable path to self-improvement" with regards to animals. Animals become more adapted to their environment; but they don't become "better animals" since a change in the environment leads them to be worse adapted. The subtlety is that, traits may be gained, and then lost, and both were "better": to gain fur as the earth cooled, and to lose it again as the earth warmed.
And finally I must ask, where has the author shown the birds are maladapted? They fly awkwardly, sure -- but what difference does it make for them?
Through that lens, there's no counterintuitive behavior here, and natural selection isn't being undermined. It's an emergent polarization.
>The clumsy wings of males could be rationalized as a handicap that provides information about the birds’ condition or genetic quality.
Also known as an honest indicator of fitness.
>But the observation that female club-wings have also probably made themselves less capable fliers can only be described as decadent —
Why the "probably" there? Previously the author mentioned that the bones where hollow in the females, unlike the males. Maybe they can fly just fine!
>sexual selection leading to a decline in the capacity for survival.
Yeah but, the fact that they exist, shows that they have survived.
So natural selection.
