系統樹

• Reading: けいとうじゅ
• Romaji: keitoju
• Kanji breakdown: 系 (kei) — lineage, thread; 統 (tou) — to unify; 樹 (ju) — tree
• Pronunciation: /keː.toː.dʑɯ/

Meaning

Phylogenetic tree; evolutionary tree. A branching diagram representing the inferred evolutionary relationships among species or other biological entities.

A fundamental concept in evolutionary biology and systematics (系統分類学). 系統樹 visually represents the evolutionary divergence of organisms from common ancestors, with branch points (分岐点) representing speciation events. Modern molecular phylogenetics (分子系統学) uses DNA and protein sequence data to construct these trees. 分子系統樹 (molecular phylogenetic tree) is a key tool in understanding biodiversity, disease evolution (ウイルスの系統樹 — viral phylogenetics), and the history of life on Earth.

Examples

1. DNA配列を比較分析することで、生物の進化的な系統樹を構築することができる。 By comparatively analysing DNA sequences, it is possible to construct an evolutionary phylogenetic tree of organisms.
2. ウイルスの系統樹を解析すれば、感染症の感染経路や起源を追跡できる。 By analysing the phylogenetic tree of a virus, the transmission routes and origins of infectious diseases can be traced.
3. 系統樹によると、チンパンジーとヒトの共通祖先は約600万年前に存在したとされる。 According to phylogenetic trees, the common ancestor of chimpanzees and humans is said to have existed approximately six million years ago.

Usage Guide

Context: biology, evolutionary biology, genetics, virology, systematics

Tone: technical, academic

Origin & History

Modern Japanese compound: 系統 (keitou) — lineage, system, pedigree + 樹 (ju) — tree. 系統 combines 系 (lineage, thread) and 統 (to unify, to govern). The metaphor of a tree for evolutionary relationships was introduced by Darwin and rendered in Japanese as 系統樹.

Cultural Context

Era: Modern

Generation: Adult

Social background: Educated