To Lions, Zebras Are Mostly Gray

http://www.theatlantic.com/science/archive/2016/01/to-lions-zebras-are-mostly-gray/427050/?single_page=true

by Hooke • 10 years ago

52 53 10 years ago

mintplant• 10 years ago

The idea that its black-and-white coat might help it blend in rather than, say, stand out seems preposterous, but there are two ways in which this could work. First, the black stripes could match dark tree trunks while the white ones match shafts of light between the trunks. Alternatively, the stripes break up the zebra's outline, making it harder to identify as a juicy piece of horse-shaped steak.

I always heard that it makes it difficult to discern individual zebras when they're gathered together in a herd, confusing their would-be predators.

hammock• 10 years ago

Check out razzle dazzle, visual camouflage for ships

http://news.usni.org/2013/03/01/camouflaged-ships-an-illustr...

theoh3• 10 years ago

Dazzle camouflage is fun but, at least originally, based on kind of specious logic.

"I suddenly got the idea that since it was impossible to paint a ship so that she could not be seen by a submarine, the extreme opposite was the answer – in other words to paint her, not for low visibility, but in such a way as to break up her form and thus confuse a submarine officer as to the course on which she was heading."

Thinking in opposites is an insidious trait that plays a big part in art and culture... but not in technology.

The dazzle scheme sounds more reasonable in this account:

"Wilkinson writes that “the painting of ships with the ‘Dazzle’ scheme is based on the general assumption that it is impossible to obtain invisibility at sea, especially where, as in the case of an attacking submarine, the object is seen against the sky with practically no sea to form a background…the only course open is to paint her in such a way as to deceive the attacker as to her size and course; this can only be done by extreme contrasts of colour and shapes which will so distort the vessel as to the symmetry and bulk.” (A Brush with Life)"

murbard2• 10 years ago

I've heard it, then did a safari in Bostwana, tested my ability to count zebras, and I can attest it is very difficult. I haven't performed the control experiment of counting horses, but I did notice that the stripes were seriously messing with my ability to detect edges.

EGreg4• 10 years ago

All these "evolutionary arguments" -- this isn't real science. It's just a bunch of "just so" stories that are tested in some of the flimsiest ways (one phenomenon demonstrated to a statistically significant degree -- therefore that must have been "the reason for the evolutionary change").

Listen, tons of features that an animal has are not correlated so highly to survival as to make enough selective pressure to make that feature come to completely dominate a population. I am very skeptical of the widely "held" assumption otherwise.

For example, lets say the human anorectal angle was specifically "evolved" for pooping while squatting. Is it a "just so" story or did the exact anorectal angle contribute SO MUCH to survival or reprosuction that it became the standard for bipedal humans?

Consider just how much relative advantage with survival and replication any given feature must have in order to come to dominate ALL the other features that are competing in the population. And this is in just one area. During a single reproduction, there are tons of genetic and epigenetic variables that could be selected for, which determine different things. Why would a specific feature in a specific part of the body, that provides merely a minor improvement at any given time, come to completely replace all other genotype expressions? I have never seen a good analysis of this, just hopeful handwaving, especially in popular books like The Selfish Gene.

facepalm3• 10 years ago

Just because many people make up evolutionary just so stories doesn't mean that there can not also be valid evolutionary explanations.

If you just say "anorectal angle evolved so that people poop squatting" it is a just so story. To make it solid you have to show the context, history and so on. For example, why is it an advantage to be able to hold your poop in?

A lot of things evolved out of serendipity and are not perfect, like those arteries going up and down the whole long neck of giraffes to bridge a short distance. But there are evolutionary explanations for it.

As for features related to survival: I think phases with more and less pressure alternate. If you made a breakthrough, say you discovered skeletons, or invented the iPhone, for a while you may have such a big advantage that you can play around with lots of fancy variants. Eventually the rest of the world catches up, pressure gets higher and the less efficient variants get weeded out.

elcapitan2• 10 years ago

Isn't most of 'anthropology' just invention of plausible sounding stories with no way to verify or falsify ever as well?

EGreg4• 10 years ago

Just having plausible-sounding evolutionary explanations isn't enough, though. You also need a way to falsify the theory. There is a good essay about this called Science as Falsification, by Karl Popper:

http://www.stephenjaygould.org/ctrl/popper_falsification.htm...

Otherwise how is it different from Marxism or Freud's theories? I can always concoct an explanation in the context of my theory. That isn't science by itself. It's demagoguery.

tim333• 10 years ago

Evolution works on very long time scales. Say a few people have a gene that gives a 0.01% increase in survival so the next generation there are 1.0001 times as many copies statistically expected. Over 100,000 generations the gene would statistically expand something like 22,000 fold. And over 1m generations 1.0001^(1e6) = 2e43 meaning most of the population would have it. I think most popular books skip math lessons - they are not so popular.

dogma1138• 10 years ago

What we found is actually the opposites evolution can and does work on very short time scales exceptionally well favorable genetic traits can propagate throughout the entire population in only a handful of generation (in the best case even under 1 generation).

Also you should really not underestimate epigenetics (which we only now beginning to understand) which play even a more vital role than random mutation as epigenetics can selectively play with gene expressions in every offspring (as well as any thing which has already been born) based on both environmental factors, the "genetic" memory of the parents, and the current experience of the mother as far as mammals go.

It seems that every part of the tree of life, from bacteria to complex life forms (what's more interesting is that mammals/marsupials, fish, birds, etc. each have their own epigentic mechanisms) have it's own internal genetic restructuring mechanism which is really not dependent on random mutations being pitted against natural selection.

Udik• 10 years ago

During a single reproduction, there are tons of genetic and epigenetic variables that could be selected for, which determine different things. Why would a specific feature in a specific part of the body, that provides merely a minor improvement at any given time, come to completely replace all other genotype expressions?

As far as I understand it, sexual reproduction with its gene shuffling allows all features to evolve simultaneously. So the genes for the anorectal angle are constantly selected across the whole population in parallel with every other gene.

zkhalique4• 10 years ago

Have you ever seen the mathematics on this? When so much is being selected "at the same time" it seems like most of the time it would never get selected in the wash. After all, selection works on an individual organism, and it's binary: either the organism survives, reproduces and passes on its genes, or not (we are not talking about DNA swapping between microorganisms here). This binary signal is supposed to be the "vote" for whether a particular combination of genes is more fit or not. But you can't just say "it's all possible given a really long time", you'd have to actually quantify what the chances are of say, the mechanism a single vote selecting simultaneously 1000 different traits, would increase the prevalence of all the "beneficial" traits. Do you have enough resolution to decide e.g. whether the bone density, color of skin or the length of legs was the factor that led to survival?

I am especially not sure why it would select the traits -- like a colorectal angle -- that would make an individual simply more comfortable rather than make a tangible difference to survival.

If we took the predictions of evolutionary theory seriously, then their contrapositive seriously too. In particular why would gay people exist if genetically homosexuality confers a much lower genetic fitness? Why do we say homosexuality is primarily genetic if evolution is true?

jules• 10 years ago

That is true but not for species that reproduce sexually. This is precisely why sexual reproduction is so successful.

dTal• 10 years ago

I agree that a lot of "evolutionary arguments" that make their way as far as popular culture are indeed post-hoc "just-so stories".

However...

Consider just how much relative advantage with survival and replication any given feature must have in order to come to dominate ALL the other features that are competing in the population

Answer: very little! This is the advantage of sexual reproduction (or at least gene transfer) - it allows us to do our evolving "in parallel". A single "feature" might only convey a tiny advantage, and you'd think it'd be swamped by all the thousands of other features - but the "experiment" is repeated zillions of times, enough to bring it out of the statistical noise. It doesn't have to "make the difference" between reproductive success and failure in any particular instance. It also bears repeating that most "features" don't spring out fully formed - most "features" only convey a tiny advantage!

Sorry if this isn't a very good explanation. You've hit upon a key aspect of evolution, and I think you're right that there isn't a good, popular layperson's explanation of the mechanism that actually tackles the statistical aspect instead of glossing over it.

EGreg4• 10 years ago

I want to reply in a very strongly worded way to this point.

There is a huge disconnect between the assertions made by proponents (like Dawkins) of evolutionary explanations, that "evolution has been proven LIKE GRAVITY at this point" and the lack of widely accessible explanation of how the most obvious statistical questions are settled in favor of the theory actually working. I don't even mean comfortably working, like "it should have taken 3 trillion years but we got lucky". I mean like, how does a binary decision select for things that are not even correlated to survival or reproduction but merely comfort? And even more astonishingly, how is it able to take such long (1000s of generations) speculative paths, without any apparent benefit until the basic version of the thing is fully formed? Combine that with the contradictory empirical evidence of punctuated equilibria broken by genetic explosions and I'm not so sure the theory is correct. Mutation and natural selection seem insufficient to explain the features we see.

But the disconnect between the dearth of actual answers (as available to someone with a mathematics background like me) with the insistence that evolution "is as sure as gravity" makes me skeptical. I find the situation very close to bullshit that is politically motivated and propagated through systematic bullying.

I should point out that this is not for religious reasons but merely because the theory seems like one of those early simple theories (like the humors or luminiferous ether) that always felt off and were too simple.

PS: just to be clear, I am not challenging the theory of common descent, but rather the proposed explanation for evolution as being completely a product of random mutation and natural selection -- evolution is a vague term which adds to the equivocation problem and is further evidence that there is strong political pressure in the scientific establishment to prop up the theory.

dragonwriter• 10 years ago

All these "evolutionary arguments" -- this isn't real science. It's just a bunch of "just so" stories that are tested in some of the flimsiest ways

That's pretty much the process of generating a scientific hypothesis, so that description itself isn't the not-science part. The not-science part is presenting such stories as conclusions and leaving them set.

nitrogen2• 10 years ago

There's a concept in electrical engineering and signal processing called superposition. It basically means that a linear circuit will process the sum of a bunch of signals the same way it would process them one at a time (in very rough terms, to the best of my recollection, etc.).

Maybe something similar applies to selective pressures; at a statistical, population-wide scale, the result of optimizing thousands of traits at the same time is mathematically equivalent to optimizing one at a time?

bauc• 10 years ago

I read some interesting research[1] where they modelled the movement of Zebra's and noticed that the stripes can create optical illusions by making them appear to be moving in the opposite direction to what they actually are.

[1] http://www.bristol.ac.uk/biology/people/martin-j-how/pub/197...

Jedd• 10 years ago

Three or four times in the past week, there's been front-page stories on HN that have reminded me of this.

Rob Newman [0] (UK activist / comedian) has recently been considering evolution[1], particularly in response to the Selfish Gene approach to evolutionary biology. He's not a fan.

Over the past couple of months his new radio show - the Entirely Accurate Encyclopaedia of Evolution[2] - has been broadcast in the UK on the BBC - a delightful combination of droll + biology/science in jokes + enlightenment.

Mentioned partly because it deals with these kinds of claims in the abstract.

Primarily because it deals with these kinds of claims specifically. In one episode he speaks about Cyclosa tremula [3] spider, who builds spider replicas from her prey - they are grey, while she is striped black & white (we finally return to the zebra analogy). When birds come to prey upon her, she bounces up and down quickly, turning herself grey - to match these replicas. He makes mention of a throw-away phrase from another paper on the subject, suggesting that Cylocsa tremula builds these facsimiles out of loneliness.

The point being that we can never really know what mechanisms other organisms are using to evolve.

  [0] https://en.wikipedia.org/wiki/Robert_Newman_(comedian)
  [1] http://www.telegraph.co.uk/culture/comedy/10322813/Robert-Newman-The-universe-Richard-Dawkins-imagines-couldnt-exist-for-five-seconds.html
  [2] http://www.bbc.co.uk/programmes/b06jm72p
  [3] https://en.wikipedia.org/wiki/Cyclosa

acqq• 10 years ago

"What I think Dawkins has done is brought back a particularly virulent form of original sin. He’s actually a deeply religious thinker – ‘We are born selfish therefore let us try to teach altruism’, 'If your genes are selfish, you are.'"

Both are surely not the quotes from Dawkins but Newman's own and wrong conclusions. Genes != whole animals (or humans). Especially the "interest" of the genes doesn't have to reflect in all aspects of the behavior to eliminate cooperation.

goldbrick2• 10 years ago

This is a really scary movement, not only because he's blatantly straw-manning both Dawkins and Darwin, but because he's a populist without proper scientific credentials subtly pushing an agenda -- we could call him the Glenn Beck to Russell Brand's Joe Rogan.

Nobody properly doing science ever suggests that we ever have all the answers and it frightens me that celebrities are so often given a podium of regressive anti-intellectualism on which to challenge the corpus of established scientific knowledge and even to misrepresent it.

awl1302• 10 years ago

I agree with your point and will add that such movements are not isolated to the non-scientific: Dawkin's use of his own public platform to push his own shockingly bad agenda. Which is to say, emotional outbursts of any kind are noise and cancel each other out in time.

firethief• 10 years ago

Organisms don't evolve; evolution is a statical process of species. The organism's metacognition about this behavior doesn't affect its evolutionary fitness, regardless of whether the spider is lonely, or thinking strategically, or perhaps just acting on instinct without any anthropomorphic higher level thought process. Whyever they think they're doing it, apparently it works.

rocky1138• 10 years ago

I feel like with a headline such as this, there should be a picture at the top of what a lion might see when it looks at a zebra.

To Lions, Zebras Are Mostly Gray

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