The Milky Way is a spiral galaxy
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There are several ways selection can affect population variation:
stabilizing selection
directional selection
diversifying selection
frequency-dependent selection
sexual selection
As natural selection influences the allele frequencies in a population, individuals can either become more or less genetically similar and the phenotypes displayed can become more similar or more disparate. In the end, natural selection cannot produce perfect organisms from scratch, it can only generate populations that are better adapted to survive and successfully reproduce in their environments through the aforementioned selections.
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The jokester, hehe
A vestigial organ, something that has yet to fall prey to evolution, but no longer serves a purpose, or the purpose it used to serve.
Counting the yearly layers can date them. The oxygen in the water molecules also holds a key to past climate. Scientists are able to use the oxygen atoms in the glacial ice as a proxy for air temperature above the glacier.
