| English | 意味 |
|---|---|
| birth rate/bɜːθ reɪt/ | 出生率 |
| death rate/deθ reɪt/ | 死亡率 |
| growth rate/ɡrəʊθ reɪt/ | 成長率 |
| doubling time/ˈdʌblɪŋ taɪm/ | 倍増時間 |
A crowded planet
- For most of history, humans were few and grew slowly.
- Then, in the last 200 years, our numbers exploded.
- From one billion to eight billion in a couple of centuries.
- Understanding why is the study of human population dynamics.
Births versus deaths
- The birth rate 出生率 is how many are born per 1000 people each year.
- The death rate 死亡率 is how many die per 1000 each year.
- The growth rate 增长率 is the birth rate minus the death rate, plus migration.
- When births outnumber deaths, the population grows.
人口の成長率は主に…によって決まります
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
成長率 = （出生率 − 死亡率）＋ 純移入・移出。
Why growth exploded
- For most of history, high birth rates were matched by high death rates.
- Then medicine, sanitation, and food supply cut the death rate sharply.
- Birth rates stayed high for a while, so the population surged.
- The gap between falling deaths and high births drove the explosion.
人類の人口増加
成長率 = 出生数 - 死亡数（＋移住）
成長は出生率と死亡率の差に依存しますが、小さな率でも時間とともに人口は倍増します。
なぜ人類は昨世紀にこれほど急速に増えたのか？
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
死亡率の低下（医薬品、衛生、食料）と高い出生率が急速な増加をもたらしました。
Doubling time
- Even a small growth rate compounds over time.
- The doubling time 倍增时间 is how long a population takes to double.
- A handy shortcut: doubling time ≈ 70 ÷ (growth rate as a percent).
- At 2% per year, a population doubles in only about 35 years.
人口が倍増するために要する時間を____時間と呼びます。
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
倍増時間 ≈ 70 ÷ （百分率での成長率）— 小さな率でも長期的には人口を倍増させます。
小さな年間成長率でも、一人の人生の間に人口が倍増することがあります。
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
年率2%の場合、人口はわずか約35年で倍増します（70 ÷ 2）。
人類の人口動態に関する正しい記述をすべて選びなさい。
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
増加する人口は資源に対する圧力を高めます。他の3つは正解です。
A "small" growth rate is not small over time. Because growth compounds, even 2% per year doubles a population in about 35 years. This is why a growth rate that sounds tiny can lead to enormous numbers within a single lifetime.
The rule of 70 in action:
- Suppose a country grows at 2% per year.
- Doubling time ≈ 70 ÷ 2 = 35 years.
- A country of 50 million would reach 100 million in just 35 years — and 200 million in 70 — from a rate that sounds modest.
Human population dynamics depend on the growth rate = birth rate − death rate (plus migration). Rapid growth came from falling death rates while birth rates stayed high. Doubling time ≈ 70 ÷ (growth rate percent), so even a small rate can double a population within a lifetime.