She's our closest relative in evolutionary terms.

就進化論而言，她是我們的近親。

And this is a modern human male, or Homo sapiens, who arose in the same historical period as the Neanderthals.

這是一個現代男性人類，即智人，與尼安德特人出現在同一歷史時期。

For certain physical differences and other reasons, Neanderthals and Homo sapiens are classified as separate species.

由於某些生理差異和其他原因，尼安德特人和智人被劃分為不同的物種。

And according to biologists, different species do not usually produce fertile offspring.

根據生物學家的研究，不同的物種通常不會產生可繁殖的後代。

But by studying our human ancestors, scientists have found that the definition of species is not so clear-cut.

但是，通過研究我們的人類祖先，科學家們發現物種的定義並不是那麼一目瞭然。

Although they were different, Neanderthals and Homo sapiens not only lived together, but also had sexual intercourse, and often.

尼安德特人和智人雖然性格不同，但他們不僅生活在一起，還經常發生性關係。

And they did produce offspring, us.

他們確實生下了後代，就是我們。

But how did sex with Neanderthals change us?

但是，與尼安德特人的性行為是如何改變我們的呢？

We often think of human evolution as happening in a straight line.

我們通常認為人類的進化是直線進行的。

But the reality is much more chaotic and fascinating.

但現實卻更加混亂和迷人。

Homo heidelbergensis, a species derived from Homo erectus, appeared in Africa approximately one million years ago.

海德堡智人（Homo heidelbergensis）是直立人（Homo erectus）的衍生物種，大約出現在一百萬年前的非洲。

After spreading across Africa, it went to Europe and Asia.

在傳遍非洲後，它又傳到了歐洲和亞洲。

The heidelbergensis that remained in Africa gave rise to us, Homo sapiens.

留在非洲的海德堡人產生了我們--智人。

Those that went to Europe evolved into Homo neanderthalensis, and those that went to Asia, into Homo denisova.

去歐洲的進化成了尼安德特人，去亞洲的進化成了丹尼索瓦人。

But the appearance of each new species did not lead to the death of the others.

但是，每個新物種的出現並沒有導致其他物種的死亡。

Around 120,000 years ago, at least six species of the genus Homo coexisted.

大約 12 萬年前，智人屬至少有六個物種共存。

And we're only talking about the species that we know of.

而且我們說的只是我們已知的物種。

These groups of hominids migrated, joined together, and separated.

這些類人猿群體遷徙、聯合、分離。

Some of these encounters were probably hostile.

其中一些遭遇可能是敵對的。

Others clearly gave rise to families of different species.

其他物種則明顯產生了不同的科。

So today, we know that everyone with Eurasian ancestry shares between one and three percent of their genes with the Neanderthals.

是以，今天我們知道，每個有歐亞血統的人都與尼安德特人共享 1%到 3%的基因。

But discovering it was not an easy process.

但發現它的過程並不容易。

In 2010, a group of scientists from the Max Planck Institute in Germany sequenced the genome of a Neanderthal fossil for the first time and compared it with ours.

2010 年，德國馬克斯-普朗克研究所的一組科學家首次對尼安德特人化石的基因組進行了測序，並與我們的基因組進行了比較。

That no Neanderthal fossils were ever found in Africa indicates that they interbred with Homo sapiens in Europe and Asia.

在非洲沒有發現尼安德特人的化石，這表明他們與歐洲和亞洲的智人雜交。

The most accepted theory is that Homo sapiens would have mixed with Neanderthals between 40 and 60,000 years ago, when they advanced from Africa to the north.

最廣為接受的理論是，智人與尼安德特人混居的時間應該是在 4 到 6 萬年前，當時他們從非洲向北推進。

This hypothesis was reinforced in 2015 when the genome of the oldest sapiens found in Europe was sequenced and it was found to have between 6 and 9 percent Neanderthal DNA.

2015 年，人們對歐洲發現的最古老智人的基因組進行了測序，發現其中有 6% 到 9% 的尼安德特人 DNA，從而進一步證實了這一假設。

That fossil was between 37 and 42,000 years old.

這塊化石的年齡在 3.7 萬年到 4.2 萬年之間。

But Neanderthal DNA didn't stay in Europe and Asia.

但尼安德特人的 DNA 並沒有留在歐洲和亞洲。

Contrary to what was believed, African populations also have some Neanderthal DNA.

與人們所認為的相反，非洲人也有一些尼安德特人的 DNA。

This likely happened when Homo sapiens descended from interbreeding with Neanderthals, migrated back to Africa around 20,000 years ago.

這很可能發生在大約 2 萬年前，智人與尼安德特人雜交後裔遷回非洲時。

And those genes we inherited from Neanderthals contributed to our evolution.

我們從尼安德特人那裡繼承的那些基因對我們的進化做出了貢獻。

These genes influence how sensitive our skin is to the sun and how our hair grows.

這些基因會影響皮膚對陽光的敏感程度和頭髮的生長方式。

Features that would have been essential when adapting to new environments.

這些功能在適應新環境時至關重要。

And may have helped Homo sapiens when they migrated to Europe and Asia.

當智人遷徙到歐洲和亞洲時，它們也可能為智人提供了幫助。

Another positive Neanderthal variant protects us from bleeding during pregnancy and prevents spontaneous abortions.

尼安德特人的另一個陽性變體可以保護我們在懷孕期間不出血，並防止自然流產。

Other variants play a role in whether we are more active during the day or at night, in psychological traits such as depression, and in our propensity to nicotine addiction.

其他變體在我們白天還是晚上更活躍、抑鬱等心理特徵以及尼古丁成癮傾向方面都起著作用。

But there are genes that may have been useful at the time and can harm us today.

但是，有些基因在當時可能是有用的，但在今天可能會對我們造成傷害。

One example is a variant that contributes to faster blood clotting.

其中一個例子是一種有助於加快血液凝結的變體。

It may have helped wounds heal faster, but now the persistence of this gene increases the risk of blood clots and strokes.

它可能有助於傷口更快癒合，但現在這種基因的持續存在卻增加了血栓和中風的風險。

Another study suggests that there is a relationship between our Neanderthal genes and COVID-19.

另一項研究表明，我們的尼安德特人基因與 COVID-19 之間存在關係。

People with this variant may be two to four times more at risk of becoming seriously ill if they are infected with coronavirus.

如果感染了冠狀病毒，這種變種的人患重病的風險可能會增加兩到四倍。

Beyond genes, very little is known about what sex was like between these two species, even whether it was consensual or not.

除了基因之外，人們對這兩個物種之間的性行為知之甚少，甚至不知道它們是否自願。

But there are studies that are beginning to clarify these practical issues.

但有些研究已開始澄清這些實際問題。

In 2017, an anthropologist from Pennsylvania State University identified traces of a type of bacteria that is present in our mouths in the tooth of a Neanderthal fossil.

2017 年，賓夕法尼亞州立大學的一位人類學家在尼安德特人化石的牙齒中發現了我們口腔中存在的一種細菌的痕跡。

She believes that this bacterium was transferred between Neanderthals and sapiens perhaps because they kissed.

她認為，這種細菌是在尼安德特人和智人之間傳播的，也許是因為他們接吻了。

There are even scientists who think that these two species may have exchanged sexually transmitted diseases, such as the human papillomavirus and herpes.

甚至有科學家認為，這兩個物種可能交換了性傳播疾病，如人類乳頭瘤病毒和皰疹。

This same exchange may have been one of the factors that contributed to the Neanderthals disappearing, and not us.

這種交換也可能是導致尼安德特人而不是我們消失的因素之一。

Discoveries about interbreeding between species have given more strength to the so-called assimilation theory.

關於物種間雜交的發現使所謂的同化理論更加有力。

Since the population of Neanderthals was much smaller, they were absorbed into the Homo sapiens community over time.

由於尼安德特人的數量要少得多，隨著時間的推移，他們被吸收到智人群體中。

According to this theory, as families of sapiens and Neanderthals merged, the distinct Neanderthal species eventually disappeared.

根據這一理論，隨著智人和尼安德特人家族的融合，獨特的尼安德特人物種最終消失了。

If you think about it, it's possible to say the Neanderthals didn't become completely extinct.

仔細想想，可以說尼安德特人並沒有完全滅絕。

They are still alive, in a way, within us.

在某種程度上，它們仍然活在我們心中。

NASA Jet Propulsion Laboratory, California Institute of Technology

美國國家航空航天局噴氣推進實驗室、加州理工學院