Biological evolution implies advance.
Biological evolution implies change.
Catholicism has changed at the expense of credibility. Rather than increase in population, as with biological organisms, the reverse occurred and is ongoing.
The analogy is meant to show how religion, much like other social institutions change over time due to a variety of reasons, just like in nature other selective pressures lead to change.
The analogy is just meant to show change, not cataloging every specific reason why an organism or a religion changes.
The present leader of the Catholics has sensibly been talking about a slimmed down Catholicism in the future, even as he makes almost simultaneous, mutually contradictory statements about his own religion.
Not surprising. Catholicism is a dying dinosaur on the brink of extinction.
A religion that is seen to change with its environment is seen as unprincipled; 'evolving religion' is a contradiction in terms. A deity who changes his mind is hardly worth following, and the Vatican tries hard to cover up this fact with its casuistry, as do the lesser cults.
The Deity doesn't matter, as often the Deity takes a backs seat to man's interests. Man has always found a way to make absolute moral imperatives ever so slightly lean towards relativism.
Today's Church is not the Church the apostles built on the instructions of Jesus, just like Moses' congregation was nothing like Jesus'. However well-intentioned they all might be, cultural pressures come in and the theology has to roll with the zeitgeist, but not so much that it appears contradictory. It's quite a juggling act, but nonetheless happens.
The bottom line is that the only thing that doesn't change is change itself.
"The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms." - Samual Adams