History of the Evolution Debate
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HISTORY |
THE THEORY |
RESULTS |
Fossil Record (pre-
1859) Millions of species have existed, but they appeared suddenly, and persisted unchanged for huge periods. |
Fossil record showed that over time, new types arose and others went extinct, but it seemed to occur in 'steps'. |
This sudden appearance of new types allowed people to retain belief in Biblical Creation, only this could not explain the huge variety of species. |
Darwin's Theory (1859 - 1900's)
New types could evolve slowly by incremental adaptation. This is how so many varieties came to populate the Earth. |
Sudden appearance was only an effect of many small changes over huge periods. |
Darwin did not explain how inherited variety arose and persisted. But he believed a complete fossil record would show many intermediate types. |
Gene Theory (1900's -1930's)
Showed hereditary variety came in discreet packets. So new varieties can arise and will persist. |
Genes allow variety to arise by mutation, and be passed on as distinct traits. |
Although genes explained variety and persistence, problem remained that most traits (like size) were continuously variable and adaptable. |
New Synthesis (1930's - 1970's)
New models showed small discrete changes in genes would spread through populations. |
Small changes will accumulate as a continuous effect. |
Darwin's thesis of continuous small accumulation is shown to be consistent with latest models of gene flow. |
New Debate (1970's - present)
Fossil record still shows evolution mostly in bursts, with long periods of stability. |
Periods of "evolution" up to 1,000 times faster than periods of "stasis". |
Models of gene flow (New Synthesis) now well proven, but debate if these alone can explain the stepped changes. |
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