
When sexual selection can lead to a decline in the capacity for survival - sparaker
https://www.nytimes.com/2017/05/05/opinion/sunday/are-these-birds-too-sexy-to-survive.html
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kevinalexbrown
I remember once from undergrad the saying '"obvious" is the most dangerous
word in mathematics.' Seeing how something _could be_ true is dramatically
different from identifying and defending that it _is_ true.

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...](http://prumlab.yale.edu/sites/default/files/prum_1997_phylogenetic_tests.pdf)).

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.

~~~
mbateman
I agree. I'm inclined to think the concepts are more subtle, not less.

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.

------
skywhopper
I will just echo the other posts here that the author of this article or his
sources severely misunderstand natural selection and the special case of
sexual selection. The most important thing to understand about evolution is
that natural selection can only work with the existing traits of an organism,
the current environment in which the organism exists, and what random changes
happen. Furthermore, every change in the phenotype of an organism has a number
of sometimes disparate impacts on its likelihood of reproductive success
within its own environment. Given all of that, we should _expect_ to see
seeming contradictions like this example.

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.

~~~
lapsock
> the author of this article or his sources severely misunderstand natural
> selection and the special case of sexual selection.

The author of this article is an Evolutionary Biology researcher at Yale. It
would be really weird if he severely misunderstood natural selection.

~~~
Analemma_
It's not a Hacker News thread unless there are a bunch of computer programmers
telling people with PhD's how ignorant they are about their own field.

~~~
qb45
The problem in this case is that TFA presented this phenomenon as some black
magic unexplainable by science, despite reasonable explanations having been
provided half century ago and popularized even among lay audience by books
like _The Selfish Gene_.

But hell if you are wrong about the general trend ;)

edit:

Really what TFA did is it just falsified some extremely naive and humanly-
subjective interpretation of the slogan "survival of the fittest", without
bothering to mention that this interpretation had already been known to be
defective years ago and there are subtler alternatives which don't have this
problem.

------
lisper
The puzzlement over the apparent reproductive disadvantages of wing-singing is
simply a reflection of a misunderstanding of how evolution works. Evolution
does not select for the reproductive fitness of species, it selects for the
reproductive fitness of _genes_. And it does not select for the _absolute_
fitness of genes, but rather for their fitness relative to competing alleles
with respect to a particular environment. The genes for wing-singing are
better at reproducing _themselves_ in an environment where manakins already
exist than the genes for alternative strategies for finding mates. That this
might hurt the reproductive fitness of the other genes that go into making
club-wing manakins matters not at all to the wing-singing genes. Genes don't
think these things through. Genes don't think at all. Some genes build things
that think, and some of those things that think end up being puzzled by the
behavior of genes, including the very genes that built them.

~~~
dekhn
You're describing this viewpoint: [https://en.wikipedia.org/wiki/Gene-
centered_view_of_evolutio...](https://en.wikipedia.org/wiki/Gene-
centered_view_of_evolution) however I don't think it's really an accepted (in
terms of evidence) theory that explains all evolution. I think most biologists
think that evolution selects at multiple levels (although likely the
underlying processes are much more complex than just that).

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.

~~~
lisper
> You're describing this viewpoint

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](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.

~~~
dekhn
I think you're trying very hard to fit the real world into a hypothesis that
doesn't make any sense.

~~~
rnabel
I would encourage you to read up on what the gene-centered view actually
states.

> that doesn't make any sense

If you look at the criticism leveled against this theory you will find that
many of them have been addressed by the proponents of the theory, in many
cases very successfully. Many things can be said about this theory but your
claim strikes me as highly unqualified.

------
bad_user
> _But 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 which individuals pass on
> their genes only if they’re chosen as mates._

TFA has a weird definition for natural selection.

Evolution has no preferences and sexual selection is natural selection.

~~~
foglerek
Agreed. This is more akin to evolution being stuck in a suboptimal (and
perhaps a dead-end) local minima - but it is still natural selection as more
pleasing features = survival on an individual scale.

~~~
ggggtez
Complex systems can spend a long time following gradient descent without
reaching the local optimal. For all we know, it's features have other
advantages, like scaring off predators.

Traits need to be considered with the ones they compete against. It's
impossible to judge the bird in isolation.

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lkrubner
The title suggests "Fisherian runaway" but the article does not.

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:

\-------------------

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").

[https://en.wikipedia.org/wiki/Fisherian_runaway](https://en.wikipedia.org/wiki/Fisherian_runaway)

------
sewercake
reminded me of a much more interesting article I read a few years ago on the
same subject: [https://www.edge.org/conversation/richard_prum-duck-sex-
aest...](https://www.edge.org/conversation/richard_prum-duck-sex-aesthetic-
evolution-and-the-origin-of-beauty)

~~~
zethraeus
A conversation with the author of this piece.

~~~
emmelaich
Which makes the article even more perplexing.

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mudil
Interesting findings, but really nothing here new about the evolutionary
biology. This is just another example of Zahavian adaptations, aka handicap
principle, "which explains the evolution of characteristics, behaviors or
structures that appear contrary to the principles of Darwinian evolution in
that they appear to reduce fitness and endanger individual organisms. Evolved
by sexual selection, these act as signals of the status of the organism,
functioning to e. g. attract mates."

[https://en.m.wikipedia.org/wiki/Amotz_Zahavi](https://en.m.wikipedia.org/wiki/Amotz_Zahavi)

------
shaq_hammer
The title reminds me of a species we're all familiar with where the females
are adopting increasingly high standards for mates based in obsolete
evolutionary preferences which have no applicability to fitness in the current
environment, and where the skills relevant to survival in the current
environment are ironically often seen as unattractive by the females, and
males who cultivate these skills often don't have the time to develop the
portions of the aforementioned obsolete traits that are trainable.

~~~
cmahler7
and guys prefer women with large breasts and wide hips, both unnecessary due
to baby formula and C-Sections.

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

~~~
shaq_hammer
Breastfeeding is much better for the baby's development than formula

~~~
shaq_hammer
This is just a plain fact, why downvote it?

------
panzer_wyrm
The human females find sense of humor attractive. That requires development of
big brain. Think how shitty big brain is - it soaks up nutrition, takes insane
amounts of protein to develop, makes the infant helpless for 12 years, diverts
resources from muscle mass and bone, makes easier death during childbirth and
permanently diminishes the ability of the mother to gather food.

This species is doomed by the chasing of this superficial attractiveness.

~~~
make3
I can't tell if this comment is being serious about not seeing the other
advantages of the bigger brain for the survival of the specie.

~~~
panzer_wyrm
Take a wild guess. Especially in context of the article which says how badly
it fucks the wings without giving any information how the species interacts
with their wider ecosystem.

------
jdpigeon
It's interesting to consider this article in light of the fact that the most
ubiquitous and successful bird species are all drab and without much sexual
dimorphism (crows, sparrows, gulls)

------
solidsnack9000
There are some things that seem odd about this author's terminology.

> ...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?

------
zethraeus
Sexual selection seems like a really interesting case of natural selection
having the property of both creating and filling an evolutionary niche.

Through that lens, there's no counterintuitive behavior here, and natural
selection isn't being undermined. It's an emergent polarization.

------
Jean-Philipe
Can't believe Idiocracy hasn't been brought up by anyone yet, a SciFi satire
about exactly this phenomenon:
[https://en.wikipedia.org/wiki/Idiocracy](https://en.wikipedia.org/wiki/Idiocracy)

------
antiquark
Bad article.

>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.

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avodonosov
If they fly worse, does it mean their capacity for survival declines?

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c3534l
> It may even lead to extinction.

So natural selection.

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erikb
I'd guess that this kind of article must gain a lot of upvotes in a hacker
forum.

------
denois
I see something in common between those birds and the modern western females.
We will see soon how well nice look can compete with artificial intelligence
for survival.

