🌳 共同祖先：生命是一棵大树🌳 Common Ancestor: Life Is One Big Tree
上一片里，化石让我们看见：生命会随时间改变。变了千百万年，各种生物之间到底是什么关系？这一片换一种眼光——把全部生命画成一棵大树。Last leaf, fossils showed us that life changes over time. After millions of years of change, how is every living thing related? This leaf offers a new way to see it — all life drawn as one big tree.
第 1 步：把生命画成一棵树Step 1: Draw all life as one tree
先看这棵树怎么长：它只有一个主干，枝头却挂满了物种。First, how does this tree grow? One single trunk — and branch tips covered with species.
树根埋在土里的那一端，是最早的生命。主干每分一次家，就多长一根新枝；每根枝头，都是今天的一个物种——猴子、鸟、蜥蜴、蘑菇、花、蜜蜂。你和蘑菇、和蒲公英，沿着枝条往回走，最后都能汇到同一个主干。枝头挨得越近，亲缘就越近。The end buried in the soil is the earliest life. Every time the trunk splits a family, a new branch grows; every branch tip is a species alive today — monkeys, birds, lizards, mushrooms, flowers, bees. You, a mushroom, a dandelion — walk back along your branches and you all reach the same trunk. The closer two tips sit, the closer the kinship.
那人类在这棵树的哪里？最近的邻居是谁？So where are humans on this tree? Who is our nearest neighbour?
第 2 步：你和黑猩猩，600 万年前是一家Step 2: You and the chimp were one family 6 million years ago
在整棵树上，人类和黑猩猩的枝头挨得最近。沿枝往回走约 600 万年，就会走到同一个分叉点——它们的共同祖先。那个祖先既不是人，也不是黑猩猩，而是一种古猿。它的后代一支走成了人，一支走成了黑猩猩。所以分家不是谁变成了谁，而是兄弟各走各的路。On the whole tree, the human tip and the chimp tip sit closest together. Walk back about 6 million years and you reach one shared fork point — their common ancestor. That ancestor was neither human nor chimp: it was an ancient ape. One branch of its descendants became us, another became chimpanzees. So a split is not one animal turning into another — it is two siblings taking different roads.
那共同祖先是不是今天的某种动物？比如猴子？So is the common ancestor some animal alive today — a monkey, perhaps?
第 3 步：祖先不是“猴子”Step 3: The ancestor is not a “monkey”
不是。共同祖先大多已经灭绝，只留下化石。比如鲸：约 5000 万年前，它的祖先古鲸生活在陆地上，四条腿能走路——它既不像今天的鲸，也不像河马。后来，一支后代下了水，慢慢成了鲸；另一支留在陆地，成了河马这一支。演化不是“猴子变成人”，而是共同祖先的后代各自分家。No. Most common ancestors are long extinct — only fossils remain. Take whales: about 50 million years ago their ancestor, an ancient four-legged whale, walked on land. It looked like neither today's whale nor a hippo. Later, one branch of its descendants went to sea and slowly became whales; another stayed on land and became the hippo line. Evolution is not “a monkey turning into a human” — it is the descendants of a common ancestor splitting up.
🎮 你来当家族树侦探（2 分钟）🎮 Your turn: family-tree detective (2 minutes)
道理讲完了。拖动时间轴，把这几对物种的分叉点拖到正确的年代——一共 4 关。Theory done. Drag the time slider and place each pair's fork at the right age — 4 levels in all.
一句话记住它：所有生命是一棵大树，枝条都能往回汇到共同祖先；人类和黑猩猩，约 600 万年前才分家。Remember it in one line: all life is one big tree whose branches join back at common ancestors; humans and chimps split only about 6 million years ago.
生命之树：枝头是物种，主干是共同祖先Tree of life: tips are species, the trunk holds common ancestors人和黑猩猩的共同祖先，生活在约 600 万年前The human–chimp common ancestor lived about 6 million years ago演化不是“猴子变人”，是共同祖先的后代分家Evolution is not “monkey to human” — it is common-ancestor descendants splitting
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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