Editor's Note: We asked several scientists from various fields what they thought were the greatest mysteries today, and then we added a few that were on our minds, too. This article is one of 15 in LiveScience's "Greatest Mysteries" series running each weekday.

From bizarre butterfly spots to rainbow-colored lizards to adaptations that allow squirrelsand even snakes to "fly," physical innovations in the natural world can be mind-boggling.

Natural selection is accepted by scientists as the main engine driving the array of organisms and their complex features. But is evolution via natural selection the only explanation for complex organisms?

"I think one of the greatest mysteries in biology at the moment is whether natural selection is the only process capable of generating organismal complexity," said Massimo Pigliucci of the Department of Ecology and Evolution at Stony Brook University in New York, "or whether there are other properties of matter that also come into play. I suspect the latter will turn out to be true."

Flexible genes

Some scientists are proposing additions to the list of evolutionary forces.

"Over the past decade or two, scientists have begun to suspect that there are other properties of complex systems (such as living organisms) that may help, together with natural selection, explain how things such as eyes, bacterial flagella, wings and turtle shells evolve," Pigliucci told LiveScience.

One idea is that organisms are equipped with the flexibility to change their physical or other features during development to accommodate environmental changes, a phenomenon called phenotypic plasticity.

The change typically doesn't show up in the genes. For instance, in social bees, both the workers and guards have the same genomes but different genes get activated to give them distinct behaviors and appearances. Environmental factors, such as temperature and embryonic diet, prompt genetic activity that ends up casting one bee a worker and the other a guard.

If beneficial, this flexibility could be passed on to offspring and so can lead to the evolution of new features in a species. "This plasticity is heritable, and natural selection can favor different kinds of plasticity, depending on the range of environmental conditions the organism encounters," Pigliucci said.

Made to order

Self-organization is another evolutionary force that some experts say whips up complex features or behaviors spontaneously in living and non-living matter, and these traits are passed on to offspring through the generations.

"A classic example outside of biology are hurricanes: These are not random air movements at all, but highly organized atmospheric structures that arise spontaneously given the appropriate environmental conditions," Pigliucci said. "There is increasing evidence that living organisms generate some of their complexity during development in an analogous manner."

A biological illustration of self-organization is protein-folding. A lengthy necklace of amino acids bends, twists and folds into a three-dimensional protein, whose shape determines the protein's function. A protein made up of just 100 amino acids could take on an endless number (billions upon billions) of shapes. While this shape-shifting takes on the order of seconds to minutes in nature, the fastest computers don't have the muscle yet to pull off the feat.

The mechanism that triggers the final form could be a chemical signal, for instance.

Novelties in nature

The environment also could drive changes in an animal's appearance or phenotype, a phenomenon that intrigues many biologists.

For instance, Sean Carroll, a molecular biologist at the University of Wisconsin-Madison, discovered butterflies in East Africa have different colorings depending on when they hatch. Those hatching during the wet season emerge with brightly colored eyespots while their dry-season relatives wear neutral cryptic coats.

Biology has a pretty good understanding of how animals develop from a fertilized egg to a fully formed organism.

"We just don't understand how ... the environment and [the] genetic blueprint interact during development," said Theunis Piersma of the Center for Ecological and Evolutionary Studies at the University of Groningen in the Netherlands.

Piersma's research on shorebirds called red knots has revealed the birds can morph their phenotypes depending on their migration routes.

When brought into captivity and placed in colder temperature environments, the shorebirds' flight muscles and organs shrink to reduce heat loss. The birds pass on to offspring the capacity to make these changes.

So the mystery is starting to clear around how diverse species with an array of features evolve. The field, which had relied in the past mostly on fossil records, got a boost with the development of genetic techniques and the integration of diverse sectors of science, connecting genetics, biology, ecology and computer science.

While scientists are shedding light on natural mechanisms that work to shape species, many questions in the field are brewing on the lab-bench. And the original question examined by Charles Darwin—what is the mechanism that causes new species to evolve—has yet to be fully explained. And another related question looms: How important are chance events, as opposed to natural selection, to shaping organisms?

编辑寄语：我们问过来自各种不同领域的几个科学家们有关他们认为当今最大的谜题是什么，然后，我们也加入了一些我们自己觉得的谜题。这篇文章是LiveScience上在每个工作日出炉的“最大谜团”系列15篇中的其中一篇。

从奇怪的蝴蝶斑纹到彩虹色的蜥蜴的改造,也让松鼠甚至蛇“飞翔”，自然界中的生理性创新可以说是令人难以置信的。

自然选择作为驱使有机体排列及其复杂特性的主要动力被科学家们所接受，但是难道通过自然选择的进化是复杂有机体的唯一解释吗？

纽约州立石溪大学生态学及进化系的Massimo Pigliucci（马西莫。匹格里奇）说：“我认为现今生物学上最大的谜团之一是，自然选择是否是产生有机体复杂性的唯一可能过程，或者，是否有其他性质的原因（物质）也起了作用，我猜想后者将会被证实。”

灵活的基因

一些科学家正建议给进化力量的单子上加些东西。

Pigliucci（匹格里奇）告诉LiveScience说，“在过去的十几二十年里，科学家们已经开始猜测是否有复杂系统（例如活体）的其他性质可能连同自然选择一起，来帮助解释诸如眼睛，细菌鞭毛，翅膀和乌龟壳的东西是怎么进化的。？”

一种观点是，有机体具有灵活性以在发展（发育）中为适应环境改变而改变它们的生理或其他特性，（这是）一种被称为表型可塑性的现象。

这种改变一般不会特别在基因中显现。比如，在蜜蜂种群中，工蜂和兵蜂拥有相同的基因组，但不同的基因被激活而赋予了它们不同的行为方式和外表。环境因素，例如温度和胚胎时的饮食，推动让一个蜜蜂成为工蜂，而另一个成为兵蜂的遗传活动宣告结束。

如果是有利的，这种灵活性可以被传递给后代，这样就可以导致种群中新特性的进化。Pigliucci（匹格里奇）说，“这种可塑性是可遗传的，而自然选择可以支持不同的可塑性，取决于有机体遇到的环境条件的排列。”

定制

自我组织是一些专家说的，在活体及非活体中自发地现出复杂特性或者行为的另一种进化力量，而这些特性一代代地传递给后代。

Pigliucci（匹格里奇）说，“生物学以外的一个经典的例子是飓风：这些根本不是什么随机的空气运动，而是在适当的环境条件下自然引发的高度有组织的大气结构。”“逐渐增加的证据显示活体在发展中以一种类似的方式来产生它们的一些复杂性。” 自我组织的一个生物学例证是蛋白质折叠。氨基酸的一个长链弯曲，扭转，折叠成一个三维的蛋白质，它的形状决定了蛋白质的功能。一个仅由100个氨基酸组成的蛋白质可以呈现无数（数十亿以上）个形状。当这种形状变化在自然界中呈现秒到分的顺序？时，最快的电脑也还没有力量来实现这种壮举。 例如，触发了最终形状的机制可能是一个化学信号。

自然界中的新奇事物

环境也可以驱使一个动物在外表或显性上的改变，这是一种激发了许多生物学家兴趣的现象。

例如，威斯康星州麦迪逊大学的一位分子生物学家Sean Carroll（西恩。卡瑞尔）发现，非洲东部的蝴蝶会有不同的颜色---它取决于它们何时孵化。那些在雨季孵化的（蝴蝶）会出现亮色的眼点，而它们在旱季孵化的亲戚们则拥有中性秘密的（中庸不显眼的？）外衣。

生物学对动物是怎么从一个受精卵发展一个完全成形的有机体有一个相当好的理解。

荷兰格罗宁根大学生态及进化学研究中心的Theunis Piersma（撒依尼斯 。皮尔斯玛）说“我们只是不理解怎么。。。环境和基因蓝图在发育中是怎么交互作用的，”

Piersma（皮尔斯玛）对被称为“红结”的岸禽类鸟的研究显示了这种鸟可以根据它们的移动路线来变化它们的显型。

当被带入囚禁状态或者被安置在较冷温度的环境下，水鸟的飞行肌肉和器官都缩小以减少热力损失。鸟类传递给后代这种能力来作出这些改变。

所以围绕着拥有一系列特性的不同物种是怎么进化的谜团开始变得清晰。过去主要依靠化石记录（来研究）的领域，连同基因技术的发展及科学不同部门间的整合得到了一个推进，连接起了遗传学，生物学，生态学和计算机科学。

正当科学家想让物种成形的自然机制透出光来(揭示其秘密)时，这个领域的许多问题也正在实验台上酝酿着。而被查尔斯。达尔文所检验的那个最本初的问题—是什么机制引发了新物种的进化—却尚未完全得到解答。而另一个相关的问题也隐约可见：对塑造有机体来说，作为自然选择的反面，随机事件有多重要？