揭開我們祖先直立行走的基因（2/2）

Recently the NY Times picked up the following:

Uncovering the Genes That Let Our Ancestors Walk Upright (2/2)

(Source: The NYT)

A new study reveals some of the crucial molecular steps on the path to bipedalism.

Origins - By Carl Zimmer who covers news about science for The Times and writes the Origins column.

Aug. 27, 2025

(continue)

Dr. Senevirathne and her colleagues found that primates develop the ilium in much the same way mice do. Two tiny rods of cartilage take shape on either side of the spine and parallel to it. The rods grow and fuse to the spine, and bone cells replace the cartilage.

Dr. Senevirathne and her colleagues figured that the human ilium had evolved from this ancient blueprint. They expected that in a human embryo each ilium would start as a rod of cartilage parallel to the spine; eventually it would stop growing in that direction and expand forward.

“Lo and behold, that’s not the case,” Dr. Capellini said. “It’s not a stepwise process. It’s actually a complete flip.”

The human ilium, the scientists were surprised to discover, starts as a rod perpendicular to the spine; one end points forward toward the belly, and the other points toward the back. The cartilage rod retains this orientation as it grows into the final shape of the ilium.

“That was really striking to us,” Dr. Capellini said. “Nowhere in the human body do you find a place where humans have just changed the way we grow altogether.”

Just as strikingly, Dr. Capellini and his colleagues found, our ilium employs the same network of genes that are active in ilium cells in mice; they just work differently.

In human embryos, ilium cells turn the genes on and off in a new pattern in response to molecules released by neighboring cells. The result is a rod of cartilage forming in a new direction.

Dr. Berthelot said that this hypothesis made sense. Other researchers have discovered that the evolution of other parts of the skeleton was driven by similar changes to existing genes. “There are not so many ways that you can change the shape of a bone,” she said.

Dr. Capellini and his colleagues argue that this flip was crucial to the evolution of bipedalism. It allowed early human ancestors to grow a new kind of pelvis that supported muscles strong enough for walking upright.

But the new study also suggests that the ilium underwent a second major change millions of years later, when humans evolved big brains. The scientists discovered that the ilium is slow to switch from cartilage to bone, lagging about 15 weeks behind the rest of the skeleton. “It’s a unique, radical shift,” Dr. Capellini said.

Dr. Capellini suspects that this shift occurred as the brains of early humans expanded about a million years ago. While a big brain likely boosted our ancestors’ mental powers, it also created new risks. The large heads of babies could get stuck in the birth canal. Natural selection favored new curves on the ilium that gave human mothers a rounder birth canal, which made deliveries easier.

Dr. Capellini’s team is eager to continue their research, to better understand the history of the pelvis and to learn how its evolution in humans made us vulnerable to certain disorders. But in May the Trump administration terminated billions of dollars of funding to Harvard, including the grant that supported the pelvis research. At the time, Dr. Capellini and his colleagues were only two years into a five-year project.

“We are all wondering what would have come next had we not lost this funding,” Dr. Capellini said.

Translation

揭開我們祖先直立行走的基因（2/2）

（繼續）

Senevirathne 博士和她的同事發現，靈長類動物的髂骨發育方式與小鼠非常相似。兩根細小的軟骨棒在脊椎兩側形成，並與其平行。這些軟骨棒生長並與脊椎融合，最終被骨細胞所取代。

Senevirathne 博士和她的同事認為，人類的髂骨正是從這古老藍圖演化而來的。他們原本預計，在人類胚胎中，每根髂骨最初都是一根與脊柱平行的軟骨棒；最終它會停止沿著該方向生長，並向前擴展。

Capellini 博士說: 「呵, 看看啊，事實並非如此」; 「這不是一個循序漸進的過程。實際上，這是一個完全的顛倒」。

科學家驚訝地發現，人類的髂骨原本是一根垂直於脊椎的軟骨棒；一端指向前方腹部，另一端指向背部。軟骨棒在最終生長成髂骨形狀的過程中，會保持這種方向。

Capellini博士說: 「這真的令我們非常震驚」;「在人體中，你找不到任何一個部位，會完全改變人類的共同生長方式」。

Capellini博士和他的同事發現，同樣令人驚訝的是，我們的髂骨所使用的基因網絡與小鼠髂骨細胞中活躍的基因網絡相同；它們只是運作方式不同。

在人類胚胎中，髂骨細胞會回應鄰近細胞釋放的分子，以新的模式開啟和關閉基因。結果是軟骨棒朝著新的方向形成。

Berthelot博士表示，這個假設是有道理的。其他研究人員發現，骨骼其他部分的演化也是由現有基因的類似變化所驅動的。她說: 「改變骨骼形狀的方法並不多」。

Capellini博士和他的同事認為，這種轉變對雙足動物的演化至關重要。它使得早期人類祖先能夠發育出一種新型的骨盆，支撐著足以直立行走的肌肉。

但這項新研究也表明，髂骨在數百萬年後經歷了第二次重大變化，當時人類進化出了更大的大腦。科學家發現，髂骨從軟骨到骨骼的轉變過程較為緩慢，比骨骼的其他部分晚了約15週。Capellini 博士說: 「這是一種獨特而徹底的轉變」。

Capellini博士推測，這種轉變發生在大約一百萬年前早期人類大腦擴張的過程中。雖然較大的大腦可能增強了我們祖先的智力，但也帶來了新的風險。嬰兒的大頭可能會卡在產道裡。自然選擇有利於髂骨呈現新的曲線，使人類母親的產道更圓潤，更容易分娩。

Capellini博士的團隊渴望繼續他們的研究，以便更好地了解骨盆的歷史，並探討其在人類中的進化如何使我們更容易患上某些不正常毛病。但今年5月，特朗普政府終止了對哈佛大學的數十億美元資助，其中包括支持骨盆研究的撥款。當時，Capellini博士和他的同事們才完成了為期五年的計劃的兩年。

Capellini博士說: 「我們都在想，如果我們沒有失去這筆資金，接下來會做些什麼」。

              So, scientists have suggested that our early ancestors became bipeds as old genes started doing new things. Some genes became active in novel places in the human embryo, while others turned on and off at different times. But in May the Trump administration terminated billions of dollars of funding to Harvard, including the grant that supported the pelvis research. It is a pity if this research will be stopped due to lack of funding. Apparent, apart from economic power and military might, leading the world in the field of scientific research is also a factor that makes the Americans great.

Note:

1. Natural selection (自然選擇)is a fundamental concept in evolutionary biology that describes the process by which individuals with favorable traits are more likely to reproduce, leading to the gradual evolution of species.