Too many cubes in my program, and FPS is low...

Hi guys, I have a program which could generate cubes infinitely, this is it:

using UnityEngine; using System.Collections;

public class GOL: MonoBehaviour {

 private bool[,] grid;

 // X Size of grid
 public int rows = 10;

 // Density of initial random squares
 public int density = 5;

 // Speed of animation
 public int speed = 10;

 // Current row
 private int currentRow = 0;

 public GameObject prefabCube;

 // Use this for initialization
 void Start () {
     grid = new bool[rows, rows];
     
     // [. . .]
     // [. . .]
     // [. . .]
     // Iterate over the rows in order to randomly choose cubes to turn on.
     for(int i = 0; i < rows; i++)
     {
         for(int j = 0; j < rows; j++)
         {
             // 
             grid[i, j] = Mathf.Floor(Random.value * density) == 0;
             //GameObject.CreatePrimitive(PrimitiveType.Cube);
         }
     }
 }
 
 // Update is called once per frame
 void Update () {

     // Every speed number of frames we add another row
     if (Time.frameCount % speed == 0)
     {

         // Tick the game of life
         for (int i = 0; i < rows; i++)
         {
             for (int j = 0; j < rows; j++)
             {
                 // Get the indices of the adjacent cubes
                 int[,] indices = new int[8, 2]{ { j , i + 1 },
                                                 { j + 1, i + 1 },
                                                 { j + 1, i },
                                                 { j + 1, i - 1 },
                                                 { j, i - 1 },
                                                 { j - 1, i - 1 },
                                                 { j - 1, i },
                                                 { j - 1, i + 1 } };

                 // Check to see if these cubes exist
                 int count = 0;
                 for(int k = 0; k < 8; k++)
                 {
                     int x = indices[k, 0];
                     int y = indices[k, 1];
                     if ( x < 0
                         || y < 0
                         || x > (rows - 1)
                         || y > (rows -1))
                     {
                         continue;
                     }

                     if(grid[x, y])
                     {
                         count++;
                     }
                 }

                 if(grid[j, i])
                 {
                     // cell is currently alive
                     if(count < 2)
                     {
                         // Die
                         grid[j, i] = false;
                     } else if( count > 3 )
                     {
                         grid[j, i] = false;
                     }
                 } else
                 {
                     // cell is currently dead
                     if (count == 3)
                     {
                         grid[j, i] = true;
                     }
                 }
             }
         }

         // Add row
         for (int i = 0; i < rows; i++)
         {
             for (int j = 0; j < rows; j++)
             {
                 // Check if this cube is alive
                 if(grid[i,j] == true)
                 {
                     // get position of cube
                     // generate cube
                     Vector3 position = new Vector3(j, 0, i);
                     GameObject cube = prefabCube;

                     // Add to parent before setting global position
                     cube.transform.SetParent(gameObject.transform);
                     cube.transform.position = position;
                 } 
             }
         }

         // Move structure up
         gameObject.transform.position += new Vector3(0, 0.5f, 0);
     }

     
 }

}

after a while, the fps would be very low, I think there is too many draw calls. Is there any way to solve this problem? Thank you