From Chris Green
The “Inside Science” on mass extinctions
(11 December) clearly sets out
current thinking on the history of life on Earth, and is right to warn again of
the effect that human activity is having on our environment.
However, it misses the most positive aspect of the story so far. We inhabit a
planet teeming with life, and for us to be here means that our ancestors, and
those of every organism alive, must have survived all five mass extinctions.
You repeat the often quoted statistic that 99.9 per cent of all species that
have ever existed are now extinct. A more awesome thought is that 100 per cent
of all species alive today have an unbroken lineage of 3.5 billion years.
How this fits in with the assertion that the average lifespan of any species
is between 1 and 10 million years I do not know. If I discovered a
billion-year-old fossil of one of my ancestors how would I recognise it?
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Of course, all this assumes that life on Earth arose only once and that
everything else has followed through evolution. But there are other
possibilities. Life may have arisen more than once, the planet may have been
“seeded” from elsewhere or perhaps a deity created a species already fully
evolved. The alternatives are as varied as human imagination.
I hope that we make the right decisions today so that our descendants, in
whatever form they may take, are around to continue the search for the truth
about our origins.
Melton Mowbray, Leicestershire
