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《人類可能是演化過程中的意外》讀後
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1. 論文要點
兩位教授根據他們對上千種不同哺乳類動物的研究，得到：「人類可能是演化過程中的意外」這個結論(見本欄第2篇文章)。
兩位教授指出：複雜性的確具有功能上的優勢；但是，並非所有哺乳類動物都向高複雜性方向演化。有些物種存留在簡單結構；有些物種則向簡單結構演化。
目前有兩個關於生物何以演化到高複雜性的理論：「自然而然論」和「『自然選擇』推動論」。前者認為「演化過程」沒有方向性；生物(如人類)具有「高複雜性」純屬意外。後者認為「演化過程」具有方向性；它並不一定蘊含「目的論」，但認為「(具有)高複雜性」是一種「進化」或「進步」。
從兩位教授論文的標題可以看出，他們傾向「自然而然論」。
2. 評論
2.1 「演化」和「進化」
「演化論」在幾十年前的名字是「進化論」；大概基於「政治正確」的考量，改為目前通行的名稱。「演化」是否相當於「進化」的議題，當然不是幾千字可以得出定論。我只在此表個態：我認為「進化論」的翻譯符合「信、達、雅」的標準。
10前我有一篇舊作討論到「進步」的概念，我相信也適用於「演化」和「進化」之爭；摘錄幾段於下。
「進步」是個動詞、副詞、和形容詞。做為一個「副詞」和「形容詞」，它蘊涵「(價值)判斷」。任何「判斷」都預設了這個或那個「性質」、「標準」、和(判斷者的)「立場/價值」。「價值判斷」則蘊涵判斷者(已有某種)的偏好或傾向。
其次，「進步」也蘊涵兩個「狀態」和比較兩者之間差異的動作。這個「差異」可以來自同一個(或同一類)行動者在不同「時間」在「刺激 -- 反應」模式上的變化；它也可以來自處於不同「空間」的行動者在「刺激 -- 反應」模式上不同的個別反應。
前者如：唐朝的「刑律」和秦朝的「刑律」相比，(在犯人的「權利」上)有沒有「進步」？
後者如：英國的「文官系統」和同時期奧圖曼帝國的「文官系統」相比，(在「行政效率」上)那一個比較「進步」？
我再舉兩個例子來強調「性質」、「標準」、和「立場/價值」與「進步」這個概念的相關性。
在多數人的觀念中，人過了35歲以後，知識、能力、和EQ都可能「進步」，但在體力和體能上通常會「退步」。人對事務或人際互動的反應有自然(天真？)和世故的區別。隨著年齡的增長，相對 於「自然」，「世故」算是「進步」或「退步」，恐怕並無定論。
(以上為該文第1-3)小節；該文後面討論到「進步」是否適用在關於「歷史」和「道德」的論述。)
2.2 目的論
如果「『演化過程』沒有方向性」的理論成立，人的生命就沒有「目的」和「意義」嗎？
從神學或「極端人類中心論」的角度看，很可能得到這個悲觀的結論。但是，我們還有其它的角度可以來考慮這個議題。
我認為：從宇宙學或生物學的理論來看，宇宙和生命都是隨機產生的；自然談不上具有「目的」和「意義」。
但是，(由於「演化過程」)我們具有「意識」、「思考能力」、和「行動能力」。因此，即使宇宙和其它生物並不具有「目的」，更無從了解什麼是「意義」；我們人類可以選擇和試圖實現某個和某些「目的」。我們人類也可以選擇和試圖維護某個和某些「意義」。這個看法來自我對沙垂和卡木兩位哲學家不成熟的理解。
本文於 修改第 1 次
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人類可能是演化過程中的意外 -Matthew Wills/Marcello Ruta
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It’s reassuring to think humans are evolution’s ultimate destination – but research shows we may be an accident
Matthew Wills/Marcello Ruta
(請至原網頁參看圖片)
Depending upon how you do the counting, there are around 9 million species on Earth, from the simplest single-celled organisms to humans.
It’s reassuring to imagine that complex bodies and brains like ours are the inevitable consequence of evolution, as if evolution had a goal. Unfortunately for human egos, a recent study comparing over a thousand mammals – the group we belong to – painted a less gratifying picture.
Evolutionary biologists in the late 18th century, including Jean-Baptiste Lamarck, reasoned that life must have an innate tendency to evolve into ever more complex forms, and believed this reflected God’s design. However, by the mid-19th century, Charles Darwin showed that natural selection has no direction, and will sometimes make organisms simpler.
Modern biologists agree that the most complex organisms have become more complex over the last 4 billion years, but they disagree about what sort of process accounts for this.
Because most organisms are still very simple, one possibility is that maximum complexity has increased “accidentally”, like the diffusion of a drop of ink in a glass of water. If true, this could be a blow to our human sense of significance as the most complex organisms.
Another theory is that increasing complexity is driven, on average, by natural selection. Sometimes selection acts on many, independent branches of the tree of life in a similar way and in parallel. This can produce similar effects in many of those branches and is known as a driven trend.
While driven trends need not imply divine purpose, they at least suggest that complexity was mostly an improvement, which is reassuring for us humans.
So which pattern is the most common in the evolution of complexity: accidental diffusion or driven trend?
Most changes and mutations are bad, and these variants are usually weeded out through a process called stabilising selection, which acts to maintain the status quo. But if most mutations make things function less well, doesn’t this make it very difficult for evolutionary novelties to arise?
In fact, evolution often operates on multiple copies of things. For example, a single gene might be duplicated within the same organism.
Provided one copy maintains its original function, the other copy can accumulate mutations without putting its bearer at an immediate disadvantage. These mutated copies are usually edited out over time, but occasionally they acquire a new function that gives an advantage.
Even more remarkably, whole genomes – every single gene in an organism – can be duplicated in one generation. Under these circumstances, there are many chances that copies of some genes will acquire a new function.
For example, sturgeons and paddle fishes underwent a whole genome duplication 250 million years ago, and this may explain how they survived the biggest ever mass extinction that wiped out 96% of other marine species.
Identical copies of structures such as segments and limbs can also be made via duplication processes. For example, millipedes have lots of legs, but they are the same design copied lots of times.
Shrimps, by contrast have many different types of legs modified for feeding, walking, swimming and brooding eggs. A biological principle called the zero force evolutionary law states that these copies will tend to become less similar by accidental diffusion alone, unless stabilising selection acts to keep the status quo. Of course, natural selection may also act to make the copies less similar if this has an advantage.
Our paper shows that increasing complexity in mammals has both diffusive and driven aspects. Rather than marching towards greater complexity, mammals evolved in lots of different directions, with only some lineages pushing the upper bounds of complexity.
Surely nature selects for complexity just a bit?
Unfortunately, there is little research addressing this question. One of the few published studies demonstrates that crustaceans (crabs, lobsters, shrimps and their relatives) evolved with a driven trend for increasing complexity over the last half a billion years.
Like crustaceans, and all vertebrates, we have bodies made of repeating blocks of tissue (called somites). These are most visible in our vertebral column (or spine) and ribs, and in the six-pack of a lean athlete. Across mammals, the number of vertebrae (the bones that make up the spine) varies and they are shaped to do different jobs in the neck, thorax, back, sacrum and tail.
Counting the number of bones in different regions can quantify one aspect of complexity across all mammals. In our study sampling over a thousand mammal species, many groups – including whales, bats, rodents, carnivores and, our own group, the primates – independently evolved complex vertebral columns. This suggests higher complexity can be a winning formula, and that selection is driving this in multiple branches of the mammal tree.
However, many other branches have a low plateau in complexity or even become simpler. Elephants, rhinos, sloths, manatees, armadillos, golden moles and platypuses all thrived despite the fact they have relatively simple vertebral columns. The direction of evolution all depends on context.
Research into the evolution of complexity has only recently started gathering pace, so there is much we still don’t know. But we do know that the story of mammalian evolution hasn’t been a directional “march of progress”, but rather has many characteristics of a random and diffusive walk.
Matthew Wills, Professor of Evolutionary Palaeobiology at the Milner Centre for Evolution, University of Bath and Marcello Ruta, Senior Lecturer, Life Sciences, University of Lincoln
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