The gradual abundance of oxygen (by product of photosynthesis) made it possible for aerobic organisms to grow more and evolve.
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You forgot to include the following choices but no worries I did this question before and the answers are:
advances in technology
increases understanding on environment
etc
Answer:
Deleterious alleles appear sporadically in a population
Explanation:
A population with a deleterious allele will have no or few individuals that have the ability to pass along these traits. These alleles appear less in a population because of selective pressure but they are not always absent. The alleles appear less often but are are not always passed on and the others that are genetically fit are able to pass along their genes. The reason the population equilibrium is not zero is because these alleles do appear but they are not necessarily passed along. These individuals may not be able to reproduce or reach the age of reproduction.
Deleterious alleles appear more often, making individuals less fit genetically, i.e. they pass fewer copies of their genes to future generations. Put another way, natural selection purges the deleterious alleles.
Human activity can affect the river ecosystems because first of all humans take the water and use it for themselves, they also pollute it, disturb the ecosystems and kill fish or oysters etc. in the ecosystems.
