7.6 Evidence of Evolution
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Fossil Record | 化石记录 | The chronicle of evolution over millions of years of geologic time engraved in the order in which fossils appear in rock strata. |
| Radiometric Dating | 放射性测年法 | A method for determining the absolute age of fossils and rocks, based on the half-life of radioactive isotopes. |
| Morphological Homology | 形态同源性 | Similarity in structures resulting from common ancestry (e.g., the forelimbs of mammals). |
| Vestigial Structure | 痕迹器官 | A feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors. |
| Molecular Evidence | 分子证据 | Similarities in DNA sequences and amino acid sequences that indicate a shared evolutionary history. |
1. Reading the Past: Fossils and Geography
Evolution is not a guess; it is a unifying biological theory supported by overwhelming scientific evidence from geographical, geological, physical, biochemical, and mathematical data.
The most tangible evidence comes from the fossil record. Fossils provide a physical timeline of extinct organisms and how they transitioned into extant (currently living) species. Fossils can be dated using a variety of reliable methods:
- Relative Dating: Determining the age based on the rock strata (layers) where the fossil is found. Deeper layers are older.
- Absolute Dating (Radiometric): Measuring the rate of decay of specific radioactive isotopes (e.g., Carbon-14 for relatively recent fossils, or Uranium for ancient rocks).
- Geographical Data: Biogeography shows that species living in the same region tend to be more closely related to each other than to species in similar environments far away.
2. Morphological Evidence
By comparing the anatomy of different organisms, scientists can find morphological homologies—features shared by common ancestry.
- Even if a bat uses its wing to fly and a whale uses its flipper to swim, the underlying bone structures (humerus, radius, ulna) are virtually identical because they inherited this blueprint from a common mammalian ancestor.
- Vestigial structures are the "leftovers" of evolution. For example, some snakes and whales have tiny, useless pelvic bones hidden inside their bodies—a morphological remnant proving they evolved from ancestors that walked on four legs.
3. The Ultimate Proof: Molecular Evidence
While bones are great, modern biology relies most heavily on biochemical and genetic evidence.
Analogy: Comparing Source Code
Imagine you find two apps on your phone that look slightly different but do the same thing. How do you know if one was copied from the other? You look at their underlying computer code. In biology, DNA is the source code. A comparison of DNA nucleotide sequences and protein amino acid sequences provides the most accurate evidence for evolution. If two species share 98% of their DNA sequence, they share a very recent common ancestor.
Furthermore, many fundamental molecular and cellular processes are completely conserved across all organisms. For example, every living thing on Earth uses DNA and RNA to carry genetic info, and almost all use the exact same metabolic pathway (Glycolysis) to break down glucose. This structural and functional evidence proves the relatedness of organisms in all domains of life.