Extract from "The Black Cloud" by Fred Hoyle
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[The black cloud is communicating with scientists on Earth]

"Your first transmission came as a surprise, for it is most unusual to
find animals with technical skills inhabiting planets which are in the
nature of extreme outposts of life."

[It] was asked why this should be so.

"For two quite simple reasons. Living on the surface of a solid body,
you are exposed to a strong gravitational force. This greatly limits
the size to which your animals can grow and hence limits the scope of
your neurological activity. It forces you to possess muscular
structures to promote movement, and it also forces you to carry
protective armour against sharp blows --- as for instance your skulls
are a necessary protection for your brains. The extra weight of muscle
and armour still further reduces the scope of your neurological
activities. Indeed your very largest animals have been mostly bone and
muscle with very little brain. As I have already said, the strong
gravitational field in which you live is the cause of this
difficulty. By and large, one only expects intelligent life to exist
in a diffuse gaseous medium, not on planets at all.

"The second unfavourable factor is your extreme lack of basic chemical
foods. For the building of chemical foods on a large scale starlight
is necessary. Your planet, however, absorbs only a very minute
fraction of the light from the Sun. At the moment I myself am building
basic chemicals at about 10,000,000,000 times the rate at which
building is occurring on the whole entire surface of your planet.

"This shortage of food chemicals leads to a tooth-and-claw existence
in which it is difficult for the first glimmerings of intellect to
gain a foothold in competition with bone and muscle. Of course once
intelligence becomes firmly established, competition with sheer bone
and muscle becomes easy, but the first steps along the road are
excessively difficult --- so much so that your own case is a rarity
among planetary life forms."

"And so much for the space travel enthusiasts," said Marlowe. "Ask
him, Harry, to what we owe the emergence of intelligence here on the
Earth."

The question was put, and after a time the answer came:

"Probably to the combination of several circumstances, among which I
would rate as most important the development about fifty million years
ago of an entirely new type of plant: the plant that you call
grass. The emergence of this plant caused a drastic reorganization of
the whole animal world, owing to the peculiarity that grass can be
cropped to ground level, in distinction from all other plants. As the
grasslands spread over the Earth those animals that could take
advantage of this peculiarity survived and developed. Other animals
declined or became extinct. It seems to have been in this major
reshuffle that intelligence was able to gain its first footing on your
planet."