diff --git a/src/lib.rs b/src/lib.rs
index aab60cbc..679acbd2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -41,6 +41,7 @@
 mod edge_buffer;
 mod error;
 pub mod nested_forward_list;
+mod samples_info;
 mod segment;
 mod simplification_buffers;
 mod simplification_common;
@@ -54,6 +55,7 @@ mod tsdef;
 
 pub use edge_buffer::EdgeBuffer;
 pub use error::ForrusttsError;
+pub use samples_info::SamplesInfo;
 pub use segment::Segment;
 pub use simplification_buffers::SimplificationBuffers;
 pub use simplification_flags::SimplificationFlags;
diff --git a/src/samples_info.rs b/src/samples_info.rs
new file mode 100644
index 00000000..2f7f1eb0
--- /dev/null
+++ b/src/samples_info.rs
@@ -0,0 +1,41 @@
+use crate::IdType;
+
+/// Information about samples used for
+/// table simpilfication.
+#[derive(Default)]
+pub struct SamplesInfo {
+    /// A list of sample IDs.
+    /// Can include both "alive" and
+    /// "ancient/remembered/preserved" sample
+    /// nodes.
+    pub samples: Vec<IdType>,
+    /// When using [``EdgeBuffer``] to record transmission
+    /// events, this list must contain a list of all node IDs
+    /// alive the last time simplification happened. Here,
+    /// "alive" means "could leave more descendants".
+    /// At the *start* of a simulation, this  should be filled
+    /// with a list of "founder" node IDs.
+    pub edge_buffer_founder_nodes: Vec<IdType>,
+}
+
+impl SamplesInfo {
+    /// Generate a new instance.
+    pub fn new() -> Self {
+        SamplesInfo {
+            samples: vec![],
+            edge_buffer_founder_nodes: vec![],
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_default() {
+        let s: SamplesInfo = Default::default();
+        assert!(s.samples.is_empty());
+        assert!(s.edge_buffer_founder_nodes.is_empty());
+    }
+}
diff --git a/src/simplification_common.rs b/src/simplification_common.rs
index 123d77fe..0ccc65ce 100644
--- a/src/simplification_common.rs
+++ b/src/simplification_common.rs
@@ -2,6 +2,7 @@
 /// functions
 use crate::simplification_logic;
 use crate::ForrusttsError;
+use crate::SamplesInfo;
 use crate::SimplificationBuffers;
 use crate::SimplificationFlags;
 use crate::SimplificationOutput;
@@ -14,7 +15,7 @@ fn setup_idmap(nodes: &[Node], idmap: &mut Vec<IdType>) {
 }
 
 pub fn setup_simplification(
-    samples: &[IdType],
+    samples: &SamplesInfo,
     tables: &TableCollection,
     flags: SimplificationFlags,
     state: &mut SimplificationBuffers,
@@ -38,7 +39,7 @@ pub fn setup_simplification(
     state.ancestry.reset(tables.num_nodes());
 
     simplification_logic::record_sample_nodes(
-        &samples,
+        &samples.samples,
         &tables,
         &mut state.new_nodes,
         &mut state.ancestry,
diff --git a/src/simplify_from_edge_buffer.rs b/src/simplify_from_edge_buffer.rs
index 2db3fbc2..97926c34 100644
--- a/src/simplify_from_edge_buffer.rs
+++ b/src/simplify_from_edge_buffer.rs
@@ -3,6 +3,7 @@ use crate::simplification_logic;
 use crate::tables::*;
 use crate::EdgeBuffer;
 use crate::ForrusttsError;
+use crate::SamplesInfo;
 use crate::Segment;
 use crate::SimplificationBuffers;
 use crate::SimplificationFlags;
@@ -28,12 +29,12 @@ impl ParentLocation {
 
 fn find_pre_existing_edges(
     tables: &TableCollection,
-    alive_at_last_simplification: &[IdType],
+    edge_buffer_founder_nodes: &[IdType],
     edge_buffer: &EdgeBuffer,
 ) -> Result<Vec<ParentLocation>, ForrusttsError> {
     let mut alive_with_new_edges: Vec<i32> = vec![];
 
-    for a in alive_at_last_simplification {
+    for a in edge_buffer_founder_nodes {
         if edge_buffer.head(*a)? != EdgeBuffer::null() {
             alive_with_new_edges.push(*a);
         }
@@ -130,8 +131,9 @@ fn process_births_from_buffer(
 ///
 /// # Parameters
 ///
-/// * `samples`:
-/// * `alive_at_last_simplification`:
+/// * `samples`: Instance of [``SamplesInfo``]. The field
+///              [``SamplesInfo::edge_buffer_founder_nodes``]
+///              must be populated. See [``EdgeBuffer``] for details.
 /// * `flags`: modify the behavior of the simplification algorithm.
 /// * `state`: These are the internal data structures used
 ///            by the simpilfication algorithm.
@@ -146,8 +148,7 @@ fn process_births_from_buffer(
 /// The input tables must be sorted.
 /// See [``TableCollection::sort_tables_for_simplification``].
 pub fn simplify_from_edge_buffer(
-    samples: &[IdType],
-    alive_at_last_simplification: &[IdType],
+    samples: &SamplesInfo,
     flags: SimplificationFlags,
     state: &mut SimplificationBuffers,
     edge_buffer: &mut EdgeBuffer,
@@ -158,7 +159,7 @@ pub fn simplify_from_edge_buffer(
 
     // Process all edges since the last simplification.
     let mut max_time = Time::MIN;
-    for n in alive_at_last_simplification {
+    for n in samples.edge_buffer_founder_nodes.iter() {
         max_time = std::cmp::max(max_time, tables.node(*n).time);
     }
     for (i, _) in edge_buffer.head_itr().rev().enumerate() {
@@ -185,7 +186,7 @@ pub fn simplify_from_edge_buffer(
     }
 
     let existing_edges =
-        find_pre_existing_edges(&tables, &alive_at_last_simplification, &edge_buffer)?;
+        find_pre_existing_edges(&tables, &samples.edge_buffer_founder_nodes, &edge_buffer)?;
 
     let mut edge_i = 0;
     let num_edges = tables.num_edges();
diff --git a/src/simplify_tables.rs b/src/simplify_tables.rs
index fb8b2497..1120905f 100644
--- a/src/simplify_tables.rs
+++ b/src/simplify_tables.rs
@@ -1,7 +1,7 @@
 use crate::simplification_common::*;
 use crate::tables::*;
 use crate::ForrusttsError;
-use crate::IdType;
+use crate::SamplesInfo;
 use crate::SimplificationBuffers;
 use crate::SimplificationFlags;
 use crate::SimplificationOutput;
@@ -26,7 +26,7 @@ use crate::SimplificationOutput;
 /// [``simplify_tables``] to keep memory allocations
 /// persistent between simplifications.
 pub fn simplify_tables_without_state(
-    samples: &[IdType],
+    samples: &SamplesInfo,
     flags: SimplificationFlags,
     tables: &mut TableCollection,
     output: &mut SimplificationOutput,
@@ -56,7 +56,7 @@ pub fn simplify_tables_without_state(
 /// The input tables must be sorted.
 /// See [``TableCollection::sort_tables_for_simplification``].
 pub fn simplify_tables(
-    samples: &[IdType],
+    samples: &SamplesInfo,
     flags: SimplificationFlags,
     state: &mut SimplificationBuffers,
     tables: &mut TableCollection,
diff --git a/src/test_simplify_tables.rs b/src/test_simplify_tables.rs
index ef954199..ce92e044 100644
--- a/src/test_simplify_tables.rs
+++ b/src/test_simplify_tables.rs
@@ -8,6 +8,7 @@ mod test {
     use crate::tsdef::{IdType, Position, Time};
     use crate::wright_fisher::*;
     use crate::ForrusttsError;
+    use crate::SamplesInfo;
     use crate::SimplificationFlags;
     use crate::SimplificationOutput;
     use crate::TableCollection;
@@ -89,10 +90,10 @@ mod test {
 
         // Now, sort and simplify the tables we got from the sim:
         tables.sort_tables_for_simplification();
-        let mut samples: Vec<IdType> = vec![];
+        let mut samples = SamplesInfo::new();
         for (i, n) in tables.nodes().iter().enumerate() {
             if n.time == num_generations {
-                samples.push(i as IdType);
+                samples.samples.push(i as IdType);
             }
         }
 
@@ -122,8 +123,8 @@ mod test {
             assert!(rv == 0);
             let rv = tskr::tsk_table_collection_simplify(
                 tsk_tables.as_mut_ptr(),
-                samples.as_ptr(),
-                samples.len() as u32,
+                samples.samples.as_ptr(),
+                samples.samples.len() as u32,
                 0,
                 std::ptr::null_mut(),
             );
diff --git a/src/wright_fisher.rs b/src/wright_fisher.rs
index 3da443dd..2b4bab19 100644
--- a/src/wright_fisher.rs
+++ b/src/wright_fisher.rs
@@ -11,6 +11,7 @@ use crate::tables::{validate_edge_table, TableCollection};
 use crate::tsdef::*;
 use crate::EdgeBuffer;
 use crate::ForrusttsError;
+use crate::SamplesInfo;
 use crate::Segment;
 use crate::SimplificationBuffers;
 use crate::SimplificationFlags;
@@ -65,7 +66,6 @@ type VecBirth = Vec<Birth>;
 struct PopulationState {
     pub parents: VecParent,
     pub births: VecBirth,
-    pub alive_at_last_simplification: Vec<IdType>,
     pub edge_buffer: EdgeBuffer,
     pub tables: TableCollection,
 }
@@ -75,7 +75,6 @@ impl PopulationState {
         PopulationState {
             parents: vec![],
             births: vec![],
-            alive_at_last_simplification: vec![],
             edge_buffer: EdgeBuffer::new(),
             tables: TableCollection::new(genome_length).unwrap(),
         }
@@ -291,17 +290,17 @@ fn recombination_breakpoints(
     }
 }
 
-fn fill_samples(parents: &[Parent], samples: &mut Vec<IdType>) {
-    samples.clear();
+fn fill_samples(parents: &[Parent], samples: &mut SamplesInfo) {
+    samples.samples.clear();
     for p in parents {
-        samples.push(p.node0);
-        samples.push(p.node1);
+        samples.samples.push(p.node0);
+        samples.samples.push(p.node1);
     }
 }
 
 fn sort_and_simplify(
     flags: SimulationFlags,
-    samples: &[IdType],
+    samples: &SamplesInfo,
     state: &mut SimplificationBuffers,
     pop: &mut PopulationState,
     output: &mut SimplificationOutput,
@@ -341,7 +340,6 @@ fn sort_and_simplify(
     } else {
         simplify_from_edge_buffer(
             samples,
-            &pop.alive_at_last_simplification,
             SimplificationFlags::empty(),
             state,
             &mut pop.edge_buffer,
@@ -354,7 +352,7 @@ fn sort_and_simplify(
 
 fn simplify_and_remap_nodes(
     flags: SimulationFlags,
-    samples: &mut Vec<IdType>,
+    samples: &mut SamplesInfo,
     state: &mut SimplificationBuffers,
     pop: &mut PopulationState,
     output: &mut SimplificationOutput,
@@ -368,10 +366,10 @@ fn simplify_and_remap_nodes(
     }
 
     if flags.contains(SimulationFlags::BUFFER_EDGES) {
-        pop.alive_at_last_simplification.clear();
+        samples.edge_buffer_founder_nodes.clear();
         for p in &pop.parents {
-            pop.alive_at_last_simplification.push(p.node0);
-            pop.alive_at_last_simplification.push(p.node1);
+            samples.edge_buffer_founder_nodes.push(p.node0);
+            samples.edge_buffer_founder_nodes.push(p.node1);
         }
     }
 }
@@ -523,7 +521,7 @@ pub fn neutral_wf(
     rng.set(params.seed);
 
     let mut pop = PopulationState::new(pop_params.genome_length);
-    let mut samples: Vec<IdType> = vec![];
+    let mut samples: SamplesInfo = Default::default();
     let mut breakpoints = vec![];
 
     // Record nodes for the first generation
@@ -535,7 +533,7 @@ pub fn neutral_wf(
     }
 
     for i in 0..pop.tables.num_nodes() {
-        pop.alive_at_last_simplification.push(i as IdType);
+        samples.edge_buffer_founder_nodes.push(i as IdType);
     }
 
     let mut simplified = false;