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From these similarities, an evolutionist infers that all life is related through one original life form.  

From these similarities, an evolutionist infers that all life is related through one original life form.  

== Scientific bases for disbelief ==

== Bases for disbelief ==

The most persuasive argument for common ancestry is existence of common DNA-based genes in diverse species. But there are at least two other plausible naturalistic explanations -- parallel evolution and horizontal gene transfer.

The most persuasive argument for common ancestry is existence of common DNA-based genes in diverse species. But there are at least three other plausible explanations -- parallel evolution, horizontal gene transfer, and [[creationism]].

There is still no good theory for how DNA-based life could have arisen from non-life. If it happened once, it may happened many times. Some people say that separate evolution might have had an entirely different genetic code, but no one knows. It may well be that DNA-based life evolved from non-life many times, and the descendants of that life are living today.

Some people who believe in evolution deny universal common ancestry.  They point out that there is still no good theory for how DNA-based life could have arisen from non-life. If it happened once, it may have happened many times. Some people say that separate evolution might have had an entirely different genetic code, but no one knows. It may well be that DNA-based life evolved from non-life many times, and the descendants of that life are living today.

It is also known that genes sometime migrate somehow from one species to another species, so having a common gene is not proof of common ancestry. Maybe there is no universal common ancestor, and important genes were spread by horizontal gene transfer.

It is also known that genes sometime migrate somehow from one species to another species, so having a common gene is not proof of common ancestry. Maybe there is no universal common ancestor, and important genes were spread by horizontal gene transfer.

== Creationist bases for disbelief ==

=== Creationism ===

Creationists argue that the inference of common ancestry cannot reasonably be drawn from the evidence, for two reasons:

Creationists argue that the inference of common ancestry cannot reasonably be drawn from the evidence, for two reasons:

* Similarity is not meaningful evidence of common ancestry

* Similarity is not meaningful evidence of common ancestry