National Geographic: Rhythms of Life Page #4

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Instinct warns them to be back

in their nests by dawn,

before sharp-eyed hawks and eagles

take to the skies.

For millions of years,

mammals were the masters of the night.

In prehistoric days dominated by

dinosaurs, smaller, warm-blooded animals

took advantage of the relative safety

of the darker hours.

But the days when mammals were forced

to hide from the coning of the light

are long since over.

Now, in rain forests round the world,

near the top of the evolutionary ladder,

you'll find agile tree-toppers ready

and willing to celebrate their place

in the sun.

These proud primates,

central American howler monkeys,

inaugurate each day

with a morning chorus,

staking their claim to the trees

and life at the top.

Higher still cling their smaller

cousins, the spider monkeys.

With few natural enemies

they rule the roost.

Grasping hands and feet give them

confidence to live life out on a limb.

And evolution has given them

a whole new point of view

stereoscopic vision.

It gives them the ability to judge

distance precisely an.

And invaluable skill

when hurtling through the treetops

Somewhere deep

in the prehistoric past,

the human line diverged from

that of monkeys and apes.

And even if we no longer get to

work vine to vine,

we still share common genes

and heritage,

and an attachment to

the daytime hours.

It's programming imprinted on us both

by the ever circling sun

and its cold celestial partner.

Lunar rhythms cast long shadows

over daily life on earth.

Though the mile-high tides of creation

have shrunk to swells of mere feet,

the rise and fall of the oceans

still exerts a powerful force.

From 240,000 miles away,

the moon's pull wields power

enough to carve the coastline

and buoy up the polar ice.

Four times a day,

the sea scours the coast,

always retreating, always returning.

It's a force both destructive

and life-giving.

Many creatures thrive here, on the

shifting boundary between sea and land.

On gentler shorelines,

each time the tide retreats,

it leaves behind a feeding ground

replenished by the sea.

The lull between high tides

sees a race for survival,

a race against the lunar clock.

These scavengers must

feed their fill now.

Sand-bubbler crabs pick food

from the net of the sand,

sorting out trapped particles of

seaweed and other plants.

They leave behind

delicate spheres of sand.

It's a temporary testament

to their labors.

Combing the territory

around their burrow,

they scar the sand with their tracks,

each lone scavenger attending to

its own hunting ground.

Other creatures march boldly forward

with the strength of numbers.

Soldier crabs sweeping the shore

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