維希德斯基教授這篇文章從演化觀點討論想像力的起源。摘譯要點於下。他另有一篇討論想像力和大腦神經科學的演講，請參考。

1.  什麼是想像力？

想像力是我們所以為「人」的主要特性之一。它指的是：
1)  對感官不能察覺到事物產生腦海中圖像的能力；
2)  對根本不存在事物產生腦海中圖像的能力。

2.  相關演化簡史

2.1 相關生理結構演化簡史

生命起源 – 34億年前
神經連接網路 -- 7億年前
大腦與脊髓 – 5.25億年前

哺乳類動物在恐龍絕跡前曾經和它們並存約1.7億年。由於前者必須躲避恐龍的捕殺並同時取得足夠賴以存活的食物，哺乳動物發展出新皮質、內嗅皮質、海馬體等大腦結構來得到「記憶」能力。這個演化了2億年的記憶系統與相關神經細胞是想像力演化過程的第一個階段。

2.2 非自主的虛構記憶

做夢是最早產生的想像活動。夢境都在睡眠的「眼球快速轉動期」階段發生。經過對各類哺乳動物是否具有這個睡眠階段的研究，科學家認為做夢大概在1.4億年前產生。科學家也發現動物能夢到它們從來沒有到過的地方(1)。

(作者舉出在夢中得到的一個發明和兩個科學領域中的重大理解。)

2.3 自主想像

「自主想像」指人們有目的的排列、組合、重疊、和用其它方式處理思想或腦海中的圖像。此能力來自大腦前額葉皮質區，故稱為前額葉皮質合成過程。

人類在什麼時候取得這個能力？ 7萬年以前人類做出來的任何東西都有可能來自此能力；但在這個時間之後，考古學家發現了大量的使用自主想像力(才可能產生)的工具、工藝品、和藝術創作。

基於前額葉皮質合成過程所產生各種形式的考古文物，於6萬5千年前大量的在全球各地區同時出現。歷史學家哈拉瑞稱此事件為「認知突破」。這個時間點和最近一次人類自非洲遷徙出來的時間相當接近。      

我們從基因分析結果可以推論(2)：少數人生來就有了能夠發展出「前額葉皮質合成過程」的基因，這些人使用根據想像力設計出的謀略和新式武器消滅了同時期的其他男性，導致自己的後代遍佈全球。

*  原文附有大量超連結，請自行參考。

附註：

1. 請參考拙作《「夢」和「意識」的假說》(尚未發表)。
2. 我看不到此超連結所指示的論文(需訂閱)，無法判斷以下陳述的可信度。直覺上我懷疑作者的說法有誇大其詞之嫌。

The Evolutionary Origins of Human Imagination

By identifying what brain structures forge new objects and scenes, scientists can look back over the course of evolution to see when creativity emerged.

ANDREY VYSHEDSKIY, 04/21/23

You can easily picture yourself riding a bicycle across the sky even though that’s not something that can actually happen. You can envision yourself doing something you’ve never done before – like water skiing – and maybe even imagine a better way to do it than anyone else.

Imagination involves creating a mental image of something that is not present for your senses to detect, or even something that isn’t out there in reality somewhere. Imagination is one of the key abilities that make us human. But where did it come from?

I’m a neuroscientist who studies how children acquire imagination. I’m especially interested in the neurological mechanisms of imagination. Once we identify what brain structures and connections are necessary to mentally construct new objects and scenes, scientists like me can look back over the course of evolution to see when these brain areas emerged – and potentially gave birth to the first kinds of imagination.

From bacteria to mammals

After life emerged on Earth around 3.4 billion years ago, organisms gradually became more complex. Around 700 million years ago, neurons organized into simple neural nets that then evolved into the brain and spinal cord around 525 million years ago.

Eventually dinosaurs evolved around 240 million years ago, with mammals emerging a few million years later. While they shared the landscape, dinosaurs were very good at catching and eating small, furry mammals. Dinosaurs were cold-blooded, though, and, like modern cold-blooded reptiles, could only move and hunt effectively during the daytime when it was warm. To avoid predation by dinosaurs, mammals stumbled upon a solution: hide underground during the daytime.

Not much food, though, grows underground. To eat, mammals had to travel above the ground – but the safest time to forage was at night, when dinosaurs were less of a threat. Evolving to be warm-blooded meant mammals could move at night. That solution came with a trade-off, though: Mammals had to eat a lot more food than dinosaurs per unit of weight in order to maintain their high metabolism and to support their constant inner body temperature around 99 degrees Fahrenheit (37 degrees Celsius).

Our mammalian ancestors had to find 10 times more food during their short waking time, and they had to find it in the dark of night. How did they accomplish this task?

To optimize their foraging, mammals developed a new system to efficiently memorize places where they’d found food: linking the part of the brain that records sensory aspects of the landscape – how a place looks or smells – to the part of the brain that controls navigation. They encoded features of the landscape in the neocortex, the outermost layer of the brain. They encoded navigation in the entorhinal cortex. And the whole system was interconnected by the brain structure called the hippocampus. Humans still use this memory system for remembering objects and past events, such as your car and where you parked it.

Groups of neurons in the neocortex encode these memories of objects and past events. Remembering a thing or an episode reactivates the same neurons that initially encoded it. All mammals likely can recall and re-experience previously encoded objects and events by reactivating these groups of neurons. This neocortex-hippocampus-based memory system that evolved 200 million years ago became the first key step toward imagination.

The next building block is the capability to construct a “memory” that hasn’t really happened.

Involuntary made-up ‘memories’

The simplest form of imagining new objects and scenes happens in dreams. These vivid, bizarre involuntary fantasies are associated in people with the rapid eye movement (REM) stage of sleep.

Scientists hypothesize that species whose rest includes periods of REM sleep also experience dreams. Marsupial and placental mammals do have REM sleep, but the egg-laying mammal the echidna does not, suggesting that this stage of the sleep cycle evolved after these evolutionary lines diverged 140 million years ago. In fact, recording from specialized neurons in the brain called place cells demonstrated that animals can “dream” of going places they’ve never visited before.

In humans, solutions found during dreaming can help solve problems. There are numerous examples of scientific and engineering solutions spontaneously visualized during sleep.

The neuroscientist Otto Loewi dreamed of an experiment that proved nerve impulses are transmitted chemically. He immediately went to his lab to perform the experiment, later receiving the Nobel Prize for this discovery.

Elias Howe, the inventor of the first sewing machine, claimed that the main innovation, placing the thread hole near the tip of the needle, came to him in a dream.

Dmitri Mendeleev described seeing in a dream “a table where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.” And that was the periodic table.

These discoveries were enabled by the same mechanism of involuntary imagination first acquired by mammals 140 million years ago.

Imagining on purpose

The difference between voluntary imagination and involuntary imagination is analogous to the difference between voluntary muscle control and muscle spasm. Voluntary muscle control allows people to deliberately combine muscle movements. Spasm occurs spontaneously and cannot be controlled.

Similarly, voluntary imagination allows people to deliberately combine thoughts. When asked to mentally combine two identical right triangles along their long edges, or hypotenuses, you envision a square. When asked to mentally cut a round pizza by two perpendicular lines, you visualize four identical slices.

This deliberate, responsive and reliable capacity to combine and recombine mental objects is called prefrontal synthesis. It relies on the ability of the prefrontal cortex located at the very front of the brain to control the rest of the neocortex.

When did our species acquire the ability of prefrontal synthesis? Every artifact dated before 70,000 years ago could have been made by a creator who lacked this ability. On the other hand, starting about that time there are various archeological artifacts unambiguously indicating its presence: composite figurative objects, such as lion-man; bone needles with an eye; bows and arrows; musical instruments; constructed dwellings; adorned burials suggesting the beliefs in afterlife, and many more.

Multiple types of archaeological artifacts unambiguously associated with prefrontal synthesis appear simultaneously around 65,000 years ago in multiple geographical locations. This abrupt change in imagination has been characterized by historian Yuval Harari as the “cognitive revolution.” Notably, it approximately coincides with the largest Homo sapiens‘ migration out of Africa.

Genetic analyses suggest that a few individuals acquired this prefrontal synthesis ability and then spread their genes far and wide by eliminating other contemporaneous males with the use of an imagination-enabeled strategy and newly developed weapons.

So it’s been a journey of many millions of years of evolution for our species to become equipped with imagination. Most nonhuman mammals have potential for imagining what doesn’t exist or hasn’t happened involuntarily during REM sleep; only humans can voluntarily conjure new objects and events in our minds using prefrontal synthesis.

This article was originally published on The Conversation. Read the original article.