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What It Means to Evolve |
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1. How can one species "turn into" another? |
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One species does not "turn into" another or several other species -- not in an instant, anyway. The evolutionary
process of speciation is how one population of a species changes over time to the point where that population is distinct
and can no longer interbreed with the "parent" population. In order for one population to diverge enough from another to
become a new species, there needs to be something to keep the populations from mixing. Often a physical boundary divides
the species into two (or more) populations and keeps them from interbreeding. If separated for long enough and presented
with sufficiently varied environmental conditions, each population takes its own distinct evolutionary path. Sometimes the
division between the populations is never breached, and reproductive isolation remains intact purely for geographical reasons.
It is possible, though, if the populations have been separate for long enough, that even if brought back together and given the
opportunity to interbreed they won't, or they won't be successful if they try.
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2. How can evolution produce complex organs like the eye? |
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In the process of natural selection, individuals in a population who are well-adapted to a particular set of environmental
conditions have an advantage over those who are not so well adapted. These individuals pass their genes and advantageous
traits to their offspring, giving the offspring the same advantages. Generation after generation, natural selection acts upon
each structure within an organ like the eye, producing incremental improvements in the process. Each tiny change in a structure
is dependent upon changes in all the other structures. In this way, individual parts of a system evolve in unison to be both
structurally and functionally compatible. Eventually, over thousands and sometimes millions of years, the small
improvements add up -- the simple, systematic process has produced an almost unfathomably complex organ.
Recently, scientists have found clues to the evolutionary pasts of some of the most complex organs, helping
to clarify how this process works.
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3. Does evolution stop once a species has become a species? |
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Evolution does not stop once a species becomes a species. Every population of living organisms is
undergoing some sort of evolution, though the degree and speed of the process varies greatly from one
group to another. Populations that experience a major change in environmental conditions, whether that
change comes in the form of a new predator or a new island to disperse to, evolve much more quickly than
do populations in a more stable set of conditions. This is because evolution is driven by natural selection, and
because when the environment changes, selective pressures change, favoring one portion of the population
more heavily than it was favored before the change.
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4. Is evolution happening now? |
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Evolution is always happening, though often at rates far too slow to be observed in a matter of days, weeks, or even years.
The effects of evolution can be felt in almost every aspect of our daily lives, though, from medical and agricultural dilemmas
to the process of choosing a good mate. In medicine, there's the question of how long the antibiotics we take now will
remain effective, given the relatively fast rate at which bacteria can evolve resistance to drugs. In agriculture, the need
to protect this year's crops is pitted against the concern that doing so will set the stage for insects to evolve pesticide
resistance. For all of us, there is the issue of decreasing biodiversity, as most scientists believe that life on Earth is currently
undergoing a mass extinction in which 50 percent or more of species will die out. These are just a few examples of ways
in which evolutionary processes affect our daily lives.
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