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diff --git a/src/main/java/org/apache/commons/math/genetics/Chromosome.java b/src/main/java/org/apache/commons/math/genetics/Chromosome.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.math.genetics;
+
+/**
+ * Individual in a population. Chromosomes are compared based on their fitness.
+ *
+ * The chromosomes are IMMUTABLE, and so their fitness is also immutable and
+ * therefore it can be cached.
+ *
+ * @since 2.0
+ * @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $
+ */
+public abstract class Chromosome implements Comparable<Chromosome>,Fitness {
+
+    /**
+     * Cached value of the fitness of this chromosome.
+     */
+    private double fitness = Double.MIN_VALUE;
+
+    /**
+     * Access the fitness of this chromosome. The bigger the fitness, the better
+     * the chromosome.
+     *
+     * Computation of fitness is usually very time-consuming task, therefore the
+     * fitness is cached.
+     *
+     * @return the fitness.
+     */
+    public double getFitness() {
+        if (this.fitness == Double.MIN_VALUE) {
+            // no cache - compute the fitness
+            this.fitness = fitness();
+        }
+        return this.fitness;
+    }
+
+    /**
+     * Compares two chromosomes based on their fitness. The bigger the fitness,
+     * the better the chromosome.
+     *
+     * @param another another chromosome to compare
+     * @return
+     * <ul>
+     *     <li>-1 if <code>another</code> is better than <code>this</code></li>
+     *     <li>1 if <code>another</code> is worse than <code>this</code></li>
+     *     <li>0 if the two chromosomes have the same fitness</li>
+     * </ul>
+     */
+    public int compareTo(Chromosome another) {
+        return ((Double)this.getFitness()).compareTo(another.getFitness());
+    }
+
+    /**
+     * Returns <code>true<code> iff <code>another</code> has the same
+     * representation and therefore the same fitness. By default, it returns
+     * false -- override it in your implementation if you need it.
+     * @param another chromosome to compare
+     * @return true if <code>another</code> is equivalent to this chromosome
+     */
+    protected boolean isSame(Chromosome another) {
+        return false;
+    }
+
+    /**
+     * Searches the <code>population</code> for another chromosome with the same
+     * representation. If such chromosome is found, it is returned, if no such
+     * chromosome exists, returns <code>null</code>.
+     *
+     * @param population
+     *            Population to search
+     * @return Chromosome with the same representation, or <code>null</code> if
+     *         no such chromosome exists.
+     */
+    protected Chromosome findSameChromosome(Population population) {
+        for (Chromosome anotherChr : population) {
+            if (this.isSame(anotherChr))
+                return anotherChr;
+        }
+        return null;
+    }
+
+    /**
+     * Searches the population for a chromosome representing the same solution,
+     * and if it finds one, updates the fitness to its value.
+     *
+     * @param population
+     *            Population to search
+     */
+    public void searchForFitnessUpdate(Population population) {
+        Chromosome sameChromosome = findSameChromosome(population);
+        if (sameChromosome != null) {
+            fitness = sameChromosome.getFitness();
+        }
+    }
+
+}