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Since English biologist Charles Darwin published On the Origin of Species in 1859,
scientists have vastly improved their knowledge of natural history. However, a
lot of information is still of the speculation, and scientists can still only
make educated guesses at certain things.
One subject that they guess about is why some 400 million
years ago, animals in the sea developed limbs (肢) that allowed them to move onto and
live on land.
Recently, an idea that occurred to the US paleontologist (古生物学家) Alfred Romer a century ago became a
hot topic once again.
Romer thought that tidal (潮汐的) pools might have led to fish gaining
limbs. Sea animals would have been forced into these pools by strong tides.
Then, they would have been made either to adapt to their new environment close
to land or die. The fittest among them grew to accomplish the transition (过渡) from sea to land.
Romer called these earliest four-footed animals “tetrapods”.
Science has always thought that this was a credible theory, but only recently
has there been strong enough evidence to support it.
Hannah Byrne is an oceanographer (海洋学家) at Uppsala University in Sweden. She
announced at the 2018 Ocean Sciences Meeting in Oregon, US, that by using
computer software, her team had managed to link Homer's theory to places where
fossil deposits (沉积物) of the earliest tetrapods were found.
According to the magazine Science, in 2014, Steven Balbus, a scientist at the University of
Oxford in the UK, calculated that 400 million years ago, when the move from
land to sea was achieved, tides were stronger than they are today. This is
because the planet was 10 percent closer to the moon than it is now.
The creatures stranded in the pools would have been
under the pressure of “survival of the fittest”, explained Mattias Green, an
ocean scientist at the UK's University of Bangor. As he told Science, “After a few days in these
pools, you become food or you run out of food... the fish that had large limbs
had an advantage because they could flip (翻转) themselves back in the water.”
As is often the case, however, there are
others who find the theory less convincing. Cambridge University's paleontologist
Jennifer Clark, speaking to Nature
magazine, seemed unconvinced. “It's only one of many ideas for the origin of
land-based tetrapods, any or all of which may have been a part of the answer,”
she said.
