4.3.8

Kinematic Self-Replicating Machines

Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.

4.3.8 Large Metazoans

We will not attempt to document here or to describe the many varied and entertaining ways in which large multicellular lifeforms including plants [1838-1840] and animals [1841-1846], and especially humans [1847-1849] along with their memetic [525] and cultural [1851-1857] structures, may undertake self-reproduction. However, the common replicative strategy may be crudely summarized as follows: First, manufacture fertile seed(s) or egg(s); second, establish an environment in which the seed(s) or egg(s) can grow into a much larger, mature adult forms; and third, use the large adult forms to manufacture more seed(s) or egg(s), repeating the cycle.

The advent of sex in reproduction (Section 5.1.9 (L1)), while useful in producing variation upon which evolution may work, nevertheless greatly complicates matters at the cellular level because two separate genomes must now be replicated, recombined, partially purged, then rejoined while keeping the final chromosome count constant. For example, in human females the primary oocytes in the ovaries remain in suspended development until the monthly onset of ovulation. At that time, during each cycle a single primary oocyte grows larger and completes meiosis I (separation of homologs): the chromosomes (two sets of 23 pairs, or 92 chromosome strands, after chromosome duplication) are recombined (genetic material is swapped between strands) with their pair members. After that, half of the chromosomes (46 strands) are expelled in a “polar body,” restoring the number of copies to two (46 chromosome strands) in the remaining secondary oocyte. The polar body is essentially a waste receptacle that receives little more than the surplus chromosomes. In humans and most vertebrates, the first polar body does not go on to meiosis II (separation of sister chromatids). Which chromosomes end up in the egg and which end up in the disposable polar body is entirely a matter of chance. After entry of a sperm cell during fertilization, the secondary oocyte completes a second meiotic division (meiosis II), yielding a fertilized egg (each of which contains only a single set of 23 maternal chromosome strands, along with the 23 paternal strands contributed by the sperm) and throwing off a second polar body (carrying off a surplus set of 23 maternal chromosome strands). Avoiding the use of gender can enhance the safety of artificial kinematic replicators (Section 5.1.9 (L1)).

Last updated on 1 August 2005