diff --git a/lib/src/evolution.rs b/lib/src/evolution.rs
index 990328cab..f285acee0 100644
--- a/lib/src/evolution.rs
+++ b/lib/src/evolution.rs
@@ -316,14 +316,39 @@ impl State {
     }
 }
 
-pub trait Evolution {
-    fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId>;
+pub enum EvolutionRef<'a, 'm: 'a, 'r: 'm> {
+    Readonly(&'a ReadonlyEvolution<'r>),
+    Mutable(&'a MutableEvolution<'m, 'r>),
+}
 
-    fn is_obsolete(&self, commit_id: &CommitId) -> bool;
+impl EvolutionRef<'_, '_, '_> {
+    pub fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId> {
+        match self {
+            EvolutionRef::Readonly(evolution) => evolution.successors(commit_id),
+            EvolutionRef::Mutable(evolution) => evolution.successors(commit_id),
+        }
+    }
 
-    fn is_orphan(&self, commit_id: &CommitId) -> bool;
+    pub fn is_obsolete(&self, commit_id: &CommitId) -> bool {
+        match self {
+            EvolutionRef::Readonly(evolution) => evolution.is_obsolete(commit_id),
+            EvolutionRef::Mutable(evolution) => evolution.is_obsolete(commit_id),
+        }
+    }
 
-    fn is_divergent(&self, change_id: &ChangeId) -> bool;
+    pub fn is_orphan(&self, commit_id: &CommitId) -> bool {
+        match self {
+            EvolutionRef::Readonly(evolution) => evolution.is_orphan(commit_id),
+            EvolutionRef::Mutable(evolution) => evolution.is_orphan(commit_id),
+        }
+    }
+
+    pub fn is_divergent(&self, change_id: &ChangeId) -> bool {
+        match self {
+            EvolutionRef::Readonly(evolution) => evolution.is_divergent(change_id),
+            EvolutionRef::Mutable(evolution) => evolution.is_divergent(change_id),
+        }
+    }
 
     /// Given a current parent, finds the new parent candidates. If the current
     /// parent is not obsolete, then a singleton set of that commit will be
@@ -340,7 +365,12 @@ pub trait Evolution {
     /// change id as A). Then C is rebased to somewhere else and becomes C'.
     /// We will choose that C' as effective successor even though it has a
     /// different change id and is not a descendant of one that does.
-    fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId>;
+    pub fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId> {
+        match self {
+            EvolutionRef::Readonly(evolution) => evolution.new_parent(old_parent_id),
+            EvolutionRef::Mutable(evolution) => evolution.new_parent(old_parent_id),
+        }
+    }
 }
 
 pub struct ReadonlyEvolution<'r> {
@@ -355,29 +385,6 @@ pub trait EvolveListener {
     fn divergent_no_common_predecessor(&mut self, commit1: &Commit, commit2: &Commit);
 }
 
-impl Evolution for ReadonlyEvolution<'_> {
-    fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId> {
-        self.get_state().successors(commit_id)
-    }
-
-    fn is_obsolete(&self, commit_id: &CommitId) -> bool {
-        self.get_state().is_obsolete(commit_id)
-    }
-
-    fn is_orphan(&self, commit_id: &CommitId) -> bool {
-        self.get_state().is_orphan(commit_id)
-    }
-
-    fn is_divergent(&self, change_id: &ChangeId) -> bool {
-        self.get_state().is_divergent(change_id)
-    }
-
-    fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId> {
-        self.get_state()
-            .new_parent(self.repo.store(), old_parent_id)
-    }
-}
-
 impl<'r> ReadonlyEvolution<'r> {
     pub fn new(repo: &'r ReadonlyRepo) -> Self {
         ReadonlyEvolution {
@@ -403,6 +410,27 @@ impl<'r> ReadonlyEvolution<'r> {
             state: self.get_state().as_ref().clone(),
         }
     }
+
+    pub fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId> {
+        self.get_state().successors(commit_id)
+    }
+
+    pub fn is_obsolete(&self, commit_id: &CommitId) -> bool {
+        self.get_state().is_obsolete(commit_id)
+    }
+
+    pub fn is_orphan(&self, commit_id: &CommitId) -> bool {
+        self.get_state().is_orphan(commit_id)
+    }
+
+    pub fn is_divergent(&self, change_id: &ChangeId) -> bool {
+        self.get_state().is_divergent(change_id)
+    }
+
+    pub fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId> {
+        self.get_state()
+            .new_parent(self.repo.store(), old_parent_id)
+    }
 }
 
 pub struct MutableEvolution<'r: 'm, 'm> {
@@ -410,29 +438,27 @@ pub struct MutableEvolution<'r: 'm, 'm> {
     state: State,
 }
 
-impl Evolution for MutableEvolution<'_, '_> {
-    fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId> {
+impl MutableEvolution<'_, '_> {
+    pub fn successors(&self, commit_id: &CommitId) -> HashSet<CommitId> {
         self.state.successors(commit_id)
     }
 
-    fn is_obsolete(&self, commit_id: &CommitId) -> bool {
+    pub fn is_obsolete(&self, commit_id: &CommitId) -> bool {
         self.state.is_obsolete(commit_id)
     }
 
-    fn is_orphan(&self, commit_id: &CommitId) -> bool {
+    pub fn is_orphan(&self, commit_id: &CommitId) -> bool {
         self.state.is_orphan(commit_id)
     }
 
-    fn is_divergent(&self, change_id: &ChangeId) -> bool {
+    pub fn is_divergent(&self, change_id: &ChangeId) -> bool {
         self.state.is_divergent(change_id)
     }
 
-    fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId> {
+    pub fn new_parent(&self, old_parent_id: &CommitId) -> HashSet<CommitId> {
         self.state.new_parent(self.repo.store(), old_parent_id)
     }
-}
 
-impl MutableEvolution<'_, '_> {
     pub fn add_commit(&mut self, commit: &Commit) {
         self.state.add_commit(commit);
     }
diff --git a/lib/src/repo.rs b/lib/src/repo.rs
index d2fc23208..5e36ec56c 100644
--- a/lib/src/repo.rs
+++ b/lib/src/repo.rs
@@ -22,7 +22,7 @@ use std::sync::{Arc, Mutex, MutexGuard};
 use thiserror::Error;
 
 use crate::commit_builder::{new_change_id, signature};
-use crate::evolution::{Evolution, MutableEvolution, ReadonlyEvolution};
+use crate::evolution::{EvolutionRef, MutableEvolution, ReadonlyEvolution};
 use crate::git_store::GitStore;
 use crate::index::ReadonlyIndex;
 use crate::local_store::LocalStore;
@@ -77,10 +77,10 @@ impl<'a, 'r> RepoRef<'a, 'r> {
         }
     }
 
-    pub fn evolution(&self) -> &'a dyn Evolution {
+    pub fn evolution(&self) -> EvolutionRef {
         match self {
-            RepoRef::Readonly(repo) => repo.evolution(),
-            RepoRef::Mutable(repo) => repo.evolution(),
+            RepoRef::Readonly(repo) => EvolutionRef::Readonly(repo.evolution()),
+            RepoRef::Mutable(repo) => EvolutionRef::Mutable(repo.evolution()),
         }
     }
 }
@@ -406,8 +406,10 @@ impl<'r> MutableRepo<'r> {
         self.view.take().unwrap()
     }
 
-    pub fn evolution(&self) -> &dyn Evolution {
-        self.evolution.as_ref().unwrap()
+    pub fn evolution<'m>(&'m self) -> &MutableEvolution<'r, 'm> {
+        let evolution: &MutableEvolution<'static, 'static> = self.evolution.as_ref().unwrap();
+        let evolution: &MutableEvolution<'r, 'm> = unsafe { std::mem::transmute(evolution) };
+        evolution
     }
 
     pub fn evolution_mut<'m>(&'m mut self) -> &'m mut MutableEvolution<'r, 'm> {
diff --git a/lib/tests/test_operations.rs b/lib/tests/test_operations.rs
index 22169f991..a66da40a3 100644
--- a/lib/tests/test_operations.rs
+++ b/lib/tests/test_operations.rs
@@ -13,7 +13,6 @@
 // limitations under the License.
 
 use jujube_lib::commit_builder::CommitBuilder;
-use jujube_lib::evolution::Evolution;
 use jujube_lib::repo::RepoRef;
 use jujube_lib::store::CommitId;
 use jujube_lib::testutils;
diff --git a/src/commands.rs b/src/commands.rs
index 9840af8f0..a601b3b90 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -36,7 +36,7 @@ use jujube_lib::commit_builder::CommitBuilder;
 use jujube_lib::conflicts;
 use jujube_lib::dag_walk::{common_ancestor, topo_order_reverse, walk_ancestors};
 use jujube_lib::evolution::evolve;
-use jujube_lib::evolution::{Evolution, EvolveListener};
+use jujube_lib::evolution::EvolveListener;
 use jujube_lib::files;
 use jujube_lib::files::DiffLine;
 use jujube_lib::git;