The universe is self-existent. Two can play this game...
There is not such thing as "evolutionary biology."
Yes, there is. It's the branch of biology concerned with the study of evolution. I happen to have a degree in it.
Right, we call them mutations.
Let's get the language right here. Mutations are changes in DNA sequence. Mutations
cause changes in the organism.
Okay but do they cause the butterfly to become something other than a butterfly?
Why should they?
Here's another example that involves a bigger innovation: one of the changes that allowed mammals to have long pregnancies with a placenta that makes close contact between mother and baby. It's a
change in the HoxA11 gene that causes HoxA11 protein to interact with another protein in a new way. HoxA11 in itself turns genes off, but together with the other protein, it's
able to turn them on. Notably, one of the genes it affects is the one for prolactin hormone, which is one of the reasons a mother's body doesn't just destroy its own offspring.
(Such a complex phenomenon as a pregnancy must have involved many more mutations, of course; this is just one example.)
Help me undertand how it is a mechanism for evolution.
I'm... not sure I understand the question? These are new genes forming out of scratch. They are one of the ways new variation is generated. Evolution works from variation. Do you mean specific traits that these genes are conferring?
I have been asking how the offspring can acquire a trait for which the parents did not have the gene for. So far no one has answered.
I just gave you two papers that evidence the origin of brand new genes. If that isn't a way to acquire new traits then nothing is.
Also, see mzungu's answer. Sickle cell trait is a
pretty big deal where malaria is common. It gives you malaria resistance, which people without the mutation don't have. BTW, said mutation is literally the simplest possible kind of mutation - just one single DNA base changed to another.
I have been out of evolutionary loop for many years. Care to give me you definition of a species?
A "species" is a collection of genetically related individuals with a really, really fuzzy border. It can't be easily and sharply defined; all definitions are rough approximations only suitable for some purposes. The biological species definition (ability to produce fertile offspring) works if you're studying the diversity of animals and how it came about. Morphospecies (things that look like X) work if you're into fossils. An ecological definition is good if you want to understand how ecosystems work.
Nature is too complicated to shoehorn, unfortunately.
(You might be surprised to hear that I don't actually
need a species definition for my work and for most of my miscellaneous interests. What matters to me is not how you divide up life into chunks but what happens to genomes over time, how different creatures are related, how you get from A to B in evolution.)