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?

編輯寄語：我們問過來自各種不同領域的幾個科學家們有關他們認為當今最大的謎題是什么，然后，我們也加入了一些我們自己覺得的謎題。這篇文章是LiveScience上在每個工作日出爐的“最大謎團”系列15篇中的其中一篇。

從奇怪的蝴蝶斑紋到彩虹色的蜥蜴的改造,也讓松鼠甚至蛇“飛翔”，自然界中的生理性創新可以說是令人難以置信的。

自然選擇作為驅使有機體排列及其復雜特性的主要動力被科學家們所接受，但是難道通過自然選擇的進化是復雜有機體的唯一解釋嗎？

紐約州立石溪大學生態學及進化系的Massimo Pigliucci（馬西莫。匹格里奇）說：“我認為現今生物學上最大的謎團之一是，自然選擇是否是產生有機體復雜性的唯一可能過程，或者，是否有其他性質的原因（物質）也起了作用，我猜想后者將會被證實。”

靈活的基因

一些科學家正建議給進化力量的單子上加些東西。

Pigliucci（匹格里奇）告訴LiveScience說，“在過去的十幾二十年里，科學家們已經開始猜測是否有復雜系統（例如活體）的其他性質可能連同自然選擇一起，來幫助解釋諸如眼睛，細菌鞭毛，翅膀和烏龜殼的東西是怎么進化的。？”

一種觀點是，有機體具有靈活性以在發展（發育）中為適應環境改變而改變它們的生理或其他特性，（這是）一種被稱為表型可塑性的現象。

這種改變一般不會特別在基因中顯現。比如，在蜜蜂種群中，工蜂和兵蜂擁有相同的基因組，但不同的基因被激活而賦予了它們不同的行為方式和外表。環境因素，例如溫度和胚胎時的飲食，推動讓一個蜜蜂成為工蜂，而另一個成為兵蜂的遺傳活動宣告結束。

如果是有利的，這種靈活性可以被傳遞給后代，這樣就可以導致種群中新特性的進化。Pigliucci（匹格里奇）說，“這種可塑性是可遺傳的，而自然選擇可以支持不同的可塑性，取決于有機體遇到的環境條件的排列。”

定制

自我組織是一些專家說的，在活體及非活體中自發地現出復雜特性或者行為的另一種進化力量，而這些特性一代代地傳遞給后代。

Pigliucci（匹格里奇）說，“生物學以外的一個經典的例子是颶風：這些根本不是什么隨機的空氣運動，而是在適當的環境條件下自然引發的高度有組織的大氣結構。”“逐漸增加的證據顯示活體在發展中以一種類似的方式來產生它們的一些復雜性。” 自我組織的一個生物學例證是蛋白質折疊。氨基酸的一個長鏈彎曲，扭轉，折疊成一個三維的蛋白質，它的形狀決定了蛋白質的功能。一個僅由100個氨基酸組成的蛋白質可以呈現無數（數十億以上）個形狀。當這種形狀變化在自然界中呈現秒到分的順序？時，最快的電腦也還沒有力量來實現這種壯舉。 例如，觸發了最終形狀的機制可能是一個化學信號。

自然界中的新奇事物

環境也可以驅使一個動物在外表或顯性上的改變，這是一種激發了許多生物學家興趣的現象。

例如，威斯康星州麥迪遜大學的一位分子生物學家Sean Carroll（西恩。卡瑞爾）發現，非洲東部的蝴蝶會有不同的顏色---它取決于它們何時孵化。那些在雨季孵化的（蝴蝶）會出現亮色的眼點，而它們在旱季孵化的親戚們則擁有中性秘密的（中庸不顯眼的？）外衣。

生物學對動物是怎么從一個受精卵發展一個完全成形的有機體有一個相當好的理解。

荷蘭格羅寧根大學生態及進化學研究中心的Theunis Piersma（撒依尼斯 。皮爾斯瑪）說“我們只是不理解怎么。。。環境和基因藍圖在發育中是怎么交互作用的，”

Piersma（皮爾斯瑪）對被稱為“紅結”的岸禽類鳥的研究顯示了這種鳥可以根據它們的移動路線來變化它們的顯型。

當被帶入囚禁狀態或者被安置在較冷溫度的環境下，水鳥的飛行肌肉和器官都縮小以減少熱力損失。鳥類傳遞給后代這種能力來作出這些改變。

所以圍繞著擁有一系列特性的不同物種是怎么進化的謎團開始變得清晰。過去主要依靠化石記錄（來研究）的領域，連同基因技術的發展及科學不同部門間的整合得到了一個推進，連接起了遺傳學，生物學，生態學和計算機科學。

正當科學家想讓物種成形的自然機制透出光來(揭示其秘密)時，這個領域的許多問題也正在實驗臺上醞釀著。而被查爾斯。達爾文所檢驗的那個最本初的問題—是什么機制引發了新物種的進化—卻尚未完全得到解答。而另一個相關的問題也隱約可見：對塑造有機體來說，作為自然選擇的反面，隨機事件有多重要？