Re: Seeds, semen, gametes and new life


"Paul Pfalzner" <paxpfax@xxxxxx> wrote in message news:do5a9l$17d5$1@xxxxxxxxxxxxxxxxxxxxxx
>
> "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote in message
> news:do24jv$4cu$1@xxxxxxxxxxxxxxxxxxxxxx
> :
> : "Paul Pfalzner" <paxpfax@xxxxxx> wrote in message
> news:do02rt$2emf$1@xxxxxxxxxxxxxxxxxxxxxx
> : > One of the most puzzling processes in biology - to me, at least, being
> a
> : > non-biologist - is the process of reproduction and the beginning of a
> new
> : > life - of a plant, a tree, a flower, or an animal.
> : > All living organisms age over time, yet when a plant produces a seed,
> a
> : > fresh new plant can grow, with fresh vigor and a youthful appearance.
> : > Ditto with animals in sexual reproduction. What process is involved
> here?
> : > How can semen or a seed from a mature organism give rise to a new
> organism
> : > with all the attributes of youth? How did nature do it?
> : > Puzzled.
> :
> : I'm not a professional, but I will attempt to answer. The key point is
> : that you were wrong to write "All living organisms age over time". That
> : is only true for complex multicellular organisms. Bacteria, among other
> : simple forms of life that reproduce simply by dividing, don't really
> : age at all. The simply get bigger (if they happen to be in a benevolent
> : environment), split in two, and start getting bigger again. Over and
> : over for millions of years.
> :
> : So, in a sense, your question ought to be "How come multicellular
> organisms
> : age?", or rather, "Why do most of the cells in a multicellular organism
> : age, but the reproductive cells do not?". A big part of the answer to
> : this revised question lies in an understanding of the processes of
> : development - the process by which a single cell becomes a multicellular
> : organism. A recent book on the topic that has received some good
> reviews
> : is "Endless Forms Most Beautiful: The New Science of Evo Devo and the
> : Making of the Animal Kingdom" by Sean B. Carroll. I haven't read it,
> but
> : it probably addresses many of your likely follow-up questions.
>
>
> OK, thanks - I can agree to rephrase my query to ask about the
> 'immortality'(?) of reproductive cells. How is it that all the cells in an
> organism - forget about bacteria - get older and less viable while the
> reproductive cells do not? Of course, if such a property did not exist,
> life as we know it could not have evolved at all. I find the question
> intriguing, though. How did evolution hit on the device of keeping some
> cells from aging - the very cells that bring about the birth of new life
> from old?

Again, I would argue that you are asking the 'wrong' question. The 'right'
question is "How did evolution hit on the device of allowing some cells
to age - the very cells that will not bring about the birth of new life?"

> The situation with plants is perhaps even more puzzling : one can renew a
> flowering plant, for example, by taking cuttings, or it renews itself by
> putting out runners. Here no special reproductive cells seem to be
> involved.

Many kinds of plant cells are 'totipotent' - that is, they can serve as
the parent of a whole new plant. But at least some kinds of plant cells
have commited themselves to differentiation into the kinds of specialized
tissues which cannot normally generate a whole new plant. That is, IIRC,
some plant cell types act like most animal cell types do.

> PS I think it is not strictly true that reproductive cells, ova and sperm,
> do not age - they do it too but much more slowly than other body cells.
> But this does need an explanation, still.

I didn't mean to say that ova and sperm don't age. I meant to say that the
cells in the ovaries and testicles from which ova and sperm are produced
don't age. But that is probably not strictly true either. I'm going to
bow out now, because I really am not an expert and there are more qualified
people here who can handle your follow-up questions.


.

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