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A team of researchers created Morpho, an open-source programmable environment that enables researchers and engineers to conduct shape optimization and design for soft materials. Applications can be for anything from artificial hearts to robot materials that mimic flesh and soft tissue.

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Research has achieved a breakthrough in eco-friendly display technology, creating highly efficient and stable blue quantum dot LEDs (QLEDs) that could power the next generation of televisions, smartphones, VR headsets and energy-efficient lighting -- without using toxic heavy metals.

Research has achieved a breakthrough in eco-friendly display technology, creating highly efficient and stable blue quantum dot LEDs (QLEDs) that could power the next generation of televisions, smartphones, VR headsets and energy-efficient lighting -- without using toxic heavy metals.

Sea ice cover in both the Antarctic and Arctic remained far below average throughout February as global average temperatures linger near record highs

It’s not at all clear that clothes make the man, or woman. However, it is clear that although animals don’t normally wear clothes (except when people dress them up for their own peculiar reasons), living things are provided by natural selection with a huge and wonderful variety. Their outfits involve many different physical shapes and styles, and they arise through various routes. For now, we’ll look briefly just at eye-catching color among animals, and the two routes by which evolution’s clothier dresses them: sexual selection and warning coloration.

Human observers are understandably taken with the extraordinary appearance of certain animals, notably birds, as well as some amphibians and insects, and, in most cases, the dressed-up elegance of males in particular. In 1860, Darwin confessed to a fellow biologist that looking at the tail of a peacock made him “sick.” Not that Darwin lacked an aesthetic sense, rather, he was troubled that his initial version of natural selection didn’t make room for animals having one. After all, the gorgeous colors and extravagant length of a peacock’s tail threatened what came to be known (by way of Herbert Spencer) as “survival of the fittest,” because all that finery seemed to add up to an immense fitness detriment. A long tail is not only metabolically expensive to grow, but it’s more liable to get caught in shrubbery, while the spectacular colors make its owner more conspicuous to potential predators.

Eventually, Darwin arrived at a solution to this dilemma, which he developed in his 1871 book, The Descent of Man and Selection in Relation to Sex. Although details have been added in the ensuing century and a half, his crashing insight—sexual selection—has remained a cornerstone of evolutionary biology.

Sexual selection is sometimes envisaged as different from natural selection, but it isn’t.

Sexual selection is sometimes envisaged as different from natural selection, but it isn’t. Natural selection is neither more nor less than differential reproduction, particularly of individuals and, thereby, genes. It operates in many dimensions, such as obtaining food, avoiding predators, surviving the vagaries of weather, resisting pathogens, and so on. And yet more on! Sexual selection is a subset of natural selection that is so multifaceted and, in some ways, so counterintuitive that it warrants special consideration, as Darwin perceived and subsequent biologists have elaborated.

The bottom line is that in many species, bright coloration—seemingly disadvantageous because it is both expensive to produce and also carries increased risk because of its conspicuousness— nonetheless can contribute to fitness insofar as it is preferentially chosen by females. In such cases, the upside of conspicuous colors increasing mating opportunities compensates for its downsides.

Bright coloration is both expensive to produce and also carries increased risk because of its conspicuousness.

Nothing in science is entirely understood and locked down, but biologists have done a pretty good job with sexual selection. A long-standing question is why, when the sexes are readily distinguishable (termed, sexual dimorphism) it is nearly always the males that are brightly colored. An excellent answer comes from the theory of parental investment, first elaborated by Robert Trivers. The basic idea is that the fundamental biological difference between males and females is not in their genitals but in the defining difference between males and females, namely, how much they invest when it comes to producing offspring. Males are defined as the sex that makes sperm (tiny gametes that are produced in prodigious numbers), while females are egg makers (producing fewer gametes and investing substantially more time and energy on each one).

Sexual selection is responsible for much of the organic world’s Technicolor drama.

As a result, males are often capable of inseminating multiple females because their parental investment in each reproductive effort can be minimal. And so, males in many species, perhaps most, gain an evolutionary advantage by mating with as many females as possible. Because nearly always there are equal numbers of males and females—an important and well-researched statistical phenomenon that deserves its own treatment—this sets up two crucial dynamics. One is male-male competition whereby males hassle with each other for access to the limiting and valuable resource of females and their literal mother load of parental investment. This in turn helps explain the frequent pattern whereby males tend to be more aggressive and outfitted with weapons and an inclination to use them.

The other dynamic, especially important for understanding the evolution of conspicuous male coloration, is female choice (known as epigamic selection). Because females are outfitted with their desirable payload of parental investment, for which males compete, females often (albeit not always) have the opportunity to choose among eager suitors. And they are disposed to go for the brightest, showiest available.

Darwin intuited this dynamic but was uncomfortable about it because at the time, it was felt that aesthetic preferences were a uniquely human phenomenon, not available to animals. Now we know better, in part because the mechanism of such preferences is rather well understood. Sexual selection is responsible for much of the organic world’s Technicolor drama, such as the red of male cardinals, the tails of peacocks, or the rainbow rear ends of mandrill monkeys, all of which make these individuals more appealing to potential mates—probably because, once they are sexually attractive, they become even more attractive according to what evolutionary biologists call the sexy son hypothesis. This involves the implicit genetic promise that females who mate with males who are thus adorned will likely produce sons who will inherit their father’s flashy good looks and will therefore be attractive to the next generation of choosing females, thereby ensuring that the prior generation female who makes such a choice will produce more grandchildren through her sexy sons.

There is a strong correlation between the degree of polygyny (number of females mated on average to a given male), or, more accurately, the ratio of variability in female reproductive success to that of males, and the amount of sexual dimorphism: the extent to which males and females of a given species differ physically. The greater the polygyny (e.g., harem size, as in elephant seals) the greater the sexual dimorphism, while monogamous species tend to be comparatively monomorphic, at least when it comes to body size and weaponry.

In most cases, female reproductive success doesn’t vary greatly among individuals, testimony to the impact of the large parental investment they provide. Female success is maximal when they get all their eggs fertilized and their offspring successfully reared, a number that typically doesn’t differ greatly from one female to another. By contrast, because of their low biologically-mandated parental investment, some males have a very large number of surviving offspring—a function of their success in male-male competition along with female choice—while others are liable to die unsuccessful, nonreproductive, typically troublemaking bachelors.

When it comes to sexual dimorphism in coloration, some mysteries persist.

When it comes to sexual dimorphism in coloration, however, some mysteries persist. Among some socially monogamous species (e.g., warblers), males sport brilliant plumage. This conundrum has been resolved to some extent by the advent of DNA fingerprinting, which has shown that social monogamy doesn’t necessarily correlate with sexual monogamy. Although males of many species have long been known to be sexually randy, verging on promiscuous, females were thought to be more monogamously inclined. However, we now know that females of many species also look for what is termed extra-pair copulations, and it seems likely that this, in turn, has selected for sexy male appearance, which outfits them to potentially take advantage of any out-of-mateship opportunities.

It still isn’t clear why and how such a preference began in the case of particular species (and why it is less developed, or, rarely, even reversed in a few), but once established it becomes what the statistician and evolutionary theorist R.A. Fisher called a “runaway process.” Furthermore, we have some rather good ideas about how this process proceeds.

One is that being impressively arrayed is an indication of somatic and genetic health, which further adds to the fitness payoff when females choose these specimens. Being brightly colored has been shown to correlate with disease resistance, relative absence of parasites, being an especially adroit forager, and the like. In most cases, brightness is physiologically difficult to achieve, which means that dramatic coloration can indicate that such living billboards are also advertising their metabolic muscularity, indicating that they’d likely contain good genetic material as well.

Being brightly colored has been shown to correlate with disease resistance, relative absence of parasites, and being an especially adroit forager.

Another, related hypothesis was more controversial when first proposed by Israeli ornithologist Amotz Zahavi, but has been increasingly supported. This is the concept of “selection for a handicap,” which acknowledges that such traits as bright coloration may well be a handicap in terms of a possessor’s survival. However, Zahavi’s “Handicap Principle” turns a seeming liability into a potential asset insofar as certain traits can be positive indicators of superior quality if their possessors are able to function effectively despite possessing them. It’s as though someone carried a 50-pound backpack and was nonetheless able to finish a race, and maybe even win it! An early criticism of this notion was that the descendants of such handicapped individuals would also likely inherit the handicap, so where’s the adaptive payoff accruing to females who choose to mate with them?

For one, there’s the acknowledged benefit of producing sons who will themselves be preferentially chosen—an intriguing case in which choosy females are more fit not through their sons, but by their grandchildren by way of those sons. In addition, there is the prospect that the choosing female’s daughters would be bequeathed greater somatic viability without their brothers’ bodily handicap. It’s counterintuitive to see bright coloration as a handicap, just as it’s counterintuitive to see a handicap as a potential advantage … but there’s little reason to trust our intuition in the face of nature’s often-confusing complexity.

There’s plenty more to the saga of sexual selection and its generation of flashy animal Beau Brummels, including efforts to explain the many exceptions to the above general patterns. It’s not much of a mystery why mammals don’t partake of flashy dress patterns, given that the class Mammalia generally has poor color vision. But what about primates, who tend to be better endowed? And what of Homo sapiens? Our species sports essentially no genetically-mediated colorful sexual dimorphism. If anything, women tend to be more elaborately adorned than men, at least in Western traditions, a gender difference that seems entirely culture-based. Moreover, among some non-Western social groups, the men get dressed up far more than the women. Clearly, there is much to be resolved, and not just for nonhuman animals.

For another look at dramatic animal patterning, let’s turn to the inverse of sexual attraction, namely, selection for being avoided.

Among the most dramatic looking animals are those whose appearance is “designed” (by natural selection) to cause others—notably predators—to stay away. An array of living things, including some truly spectacular specimens, are downright poisonous, not just in their fangs or stingers but in their very bodies. When they are caterpillars, monarch butterflies feed exclusively on milkweed plants, which contain potent chemical alkaloids that taste disgusting and cause severe digestive upset to animals—especially birds— that eat them, or just venture an incautious nibble.

In the latter case, most birds with a bellyache avoid repeating their mistake although this requires, in turn, that monarchs be sufficiently distinct in their appearance that they carry an easily recognized warning sign. Hence, their dramatic black and bright orange patterning. To the human eye, they are quite lovely. To the eyes of a bird with a terrible taste in its mouth and a pain in its gut, that same conspicuous black and orange is memorable as well, recalling a meal that should not be repeated. It exemplifies “warning coloration,” an easily recalled and highly visible reminder of something to avoid. (It is no coincidence that school buses, ambulances, and fire trucks are also conspicuously colored, although here the goal is enhanced visibility per se, not advertising that these vehicles are bad to eat!)

It is no coincidence that school buses, ambulances, and fire trucks are also conspicuously colored.

The technical term for animal warning signals is aposematic, derived by combining the roots for “apo” meaning away (as in apostate, someone who moves away from a particular belief system) and “sema” meaning signal (as in semaphore). Unpalatable or outright poisonous prey species that were less notable and thus easily forgotten will have achieved little benefit from their protective physiology. And of course, edible animals that are easily recognized would be in even deeper trouble. The adaptive payoff of aposematic coloration even applies if a naïve predator kills a warningly-colored individual, because such sacrifice is biologically rewarded through kin selection when a chastened predator avoids the victim’s genetic relatives.

Many species of bees and wasps are aposematic, as are skunks: once nauseated, or stung, or subjected to stinky skunk spray, twice shy. However, chemically-based shyness isn’t the only way to train a potential predator. Big teeth or sharp claws could do the trick, just by their appearance, without any augmentation. Yet when the threat isn’t undeniably baked into an impressive organ—for example, when it is contained within an animal’s otherwise invisible body chemistry—that’s where a conspicuous, easy-to-remember appearance comes in.

Bright color does triple duty, not only warning off predators and helping acquire mates, but also signaling that brighter and hence healthier individuals are more effective fighters.

Some of the world’s most extraordinary painterly palettes (at least to the human eye) are flaunted by neotropical amphibians known as “poison arrow frogs,” so designated because their skin is so lethally imbued that indigenous human hunters use it to anoint their darts and arrow points. There is no reason, however, for the spectacular coloration of these frogs to serve only as a warning to potential frog-eating predators. As with other dramatically accoutered animals, colorfulness itself often helps attract mates, and not just by holding out the prospect of making sexy sons. Moreover, it has been observed in at least one impressively aposematic amphibian—the scrumptious-looking but highly toxic strawberry poison frog—that bright color does triple duty, not only warning off predators and helping acquire mates, but also signaling to other strawberry poison frogs that brighter and hence healthier individuals are more effective fighters.

Warning coloration occurs in a wide range of living things, evolving pretty much whenever one species develops a deserved reputation for poisonousness, ferocity, or some other form of legitimate threat. Once established, it also opens the door to further evolutionary complexity, including Batesian mimicry, first described in detail by the nineteenth-century English naturalist Henry Walter Bates who researched butterflies in the Amazon rainforest. He noticed that warningly-colored species serve as models, which are then copied by mimics that are selected to piggyback on the reputation established by the former. Brightly banded coral snakes (venomous) are also mimicked, albeit imperfectly, by some species of (nonpoisonous) king snakes. Bees and wasps, with their intimidating stings, have in most cases evolved distinctive color patterns, often bands of black and yellow; they, in turn, are mimicked by a number of other insects that are outfitted with black and yellow bands though they are stingless.

The honestly-clothed signaler can become a model to be mimicked by other species that may not be dangerous to eat but are mistaken for the real (and toxic) McCoy

In short, the honestly-clothed signaler can become a model to be mimicked by other species that may not be dangerous to eat but are mistaken for the real (and toxic) McCoy. Those monarch butterflies, endowed with poisonous, yucky-tasting alkaloids, are mimicked by another species—aptly known as “viceroys” (substitute monarchs)—that bypass the metabolically expensive requirement of dealing with milkweed toxins while benefiting by taking advantage of the monarch’s legitimately acquired reputation.

The plot thickens. Viceroy butterflies (the mimic) and monarchs (the model) can both be successful as long as the mimics aren’t too numerous. A problem arises, however, when viceroys become increasingly abundant, because the more viceroys, the more likely it is that predators will nibble on those harmless mimics rather than being educated by sampling mostly monarchs and therefore trained to avoid their black-and-orange pattern. As a result, the well-being of both monarchs and viceroys is diminished in direct proportion as the latter become abundant, which in turn induces selection of monarchs that are discernibly different from their mimics so as not to be tarred with viceroys’ innocuousness. But the process isn’t done. As the models flutter away from their mimics, the latter can be expected to pursue them, in an ongoing process of evolutionary tag set in motion by the antipredator adaptation represented by the model’s warning coloration, the momentum of which is maintained by the very different challenges—to both the mimic and the model—generated by the system itself.

Frequency-dependent selection is a phenomenon in which the evolutionary success of a biological type varies inversely with its abundance.

This general phenomenon is known as “frequency-dependent selection,” in which the evolutionary success of a biological type varies inversely with its abundance: favored when rare, diminishing as it becomes more frequent. It’s as though certain traits carry within them the seeds of their own destruction, or at least, of keeping their numbers in check, either arriving at a balanced equilibrium or by producing a pattern of pendulum-like fluctuations.

Meanwhile, Batesian mimicry isn’t the only copycat clothing system to have evolved. Plenty of black-and-yellow-banded insects, for example, are equipped with stings, although many other warning patterns are clearly available. Different species could have used their unique pattern of colors as well as alternative designs such as spots and blotches instead of the favored black-and-yellow bands. At work here is yet another evolution-based aposematic phenomenon, known as Müllerian mimicry, after the German naturalist Fritz Müller. In this kind of mimicry, everyone is a model, because different species that are legitimately threatening in their own right converge on the same pattern. Here, the adaptive advantage is that sharing the same warning appearance facilitates learning by predators: it’s easier to learn to avoid one basic warning signal than a variety, different for each species. It had been thought that Batesian and Müllerian mimicry were opposites, with Batesian being dishonest because the mimic is essentially a parasite of its model’s legitimate reputation (those viceroys), whereas Müllerian mimicry exemplifies shared honesty, as with different species of wasps, bees, and hornets, whose fearsome reputations enhance each others.

It is currently acknowledged, however, that often the distinction is not absolute; within a given array of similar-looking Müllerian mimics, for example, not all species are equally honest when it comes to their decorative signaling. The less dangerous representatives are therefore somewhat Batesian. Conversely, among some species, assemblages that have traditionally been thought to involve Batesian mimics—including the iconic monarch–viceroy duo—mimics are often a bit unpleasant in their own right, so both participants are to some degree Müllerian convergers as well.

What to make of all this? In his book, Unweaving the Rainbow, Richard Dawkins gave us some advice, as brilliant as the colors and patterns of the natural world:

After sleeping through a hundred million centuries, we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life. Within decades we must close our eyes again. Isn’t it a noble and enlightened way of spending our time in the sun, to work at understanding the universe and how we have come to wake up in it?

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