GED Science Practice Test: Evidence of Evolution
At the heart of evolutionary theory is the basic idea that life has existed for billions of years and has changed over time. Overwhelming evidence supports this fact. While scientists continue to debate certain details of evolution, the fact that the earth and living things have a long history (over many millions of years) has been supported by a significant amount of evidence. Below are some examples of lines of evidence support Darwin’s theory of evolution by natural selection.
Fossil Evidence: The fossil record contains many well-documented examples of the transition from one species into another, as well as the origin of new physical features. Evidence from the fossil record is unique, because it provides a time perspective for understanding the evolution of life on Earth. The example below shows fossil record evidence of the evolution of the modern horse from an ancestral species. Evolutionary changes can be observed in structures such as the number of toes on each foot, shape and size of skull, body size and proportions, and structure of molar teeth.
Homologous Structures: Evolutionary theory predicts that related organisms will share similarities that are derived from common ancestors. Similar characteristics or anatomical structures due to common ancestry are known as homologous structures, or homologies. Homologies can be revealed by comparing the anatomies of different living things, looking at cellular similarities and differences, studying embryological development, and studying vestigial structures within individual organisms. In general, the more similar the homologies, the more closely related the two species are.
Vestigial Structures: Vestigial structures are organs or parts (for example, the human appendix) which are “leftover” structures that were functional in ancestral species but are not longer used for a purpose in the present-day species. Vestigial structures are usually greatly reduced from the original ancestral form; e.g. a dolphins and whales have a small vestigial pelvis bone that is a leftover from their land-dwelling ancestors. Another example of a vestigial structure is the appendix in humans. As far as we know, the appendix serves no purpose for humans, though some hypothesize that it serves as a store for beneficial bacteria in your intestines. Vestigial structures provide a clue to the evolutionary history of a species because they are remnants of structures found in the ancestral species.
Intermediate Forms: Intermediate forms are animals or fossils that have characteristics of two closely related species, or characteristics halfway between two closely related species. The fossils of Archeopteryx represent an animal that was a transitional form between a dinosaur and a bird:
Molecular evidence: Comparison of the DNA genetic sequences of organisms has revealed that species that are more closely related have a higher degree of DNA sequence similarity than species that are more distantly related. Additionally, similarities in biochemistry and molecules in all organisms are more evidence that all living things have a common ancestor. The following picture shows what percentage of the human genome (the total collection of genetic information) we share with other organisms:
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