Alistair MacLeod.
Scottish geologist,
enthusiastic rock
botherer.

The Earth always
has another
story to tell!

I lost my left hand
on a field
expedition. These
days, I change the
attachment to suit
the job.

Mostly geology.
Occasionally
opening a stubborn
biscuit tin.

Chisel, hand lens,
compass-clinometer,
GPS and altimeter.

My left hand has
more field equipment
than my luggage.

Mini shovel

One left wrist. 
A very unreasonable packing list.

Geological hammer

Jacob’s staff for
measuring strata

Sampling drill

Bali has barbets.
Nearby Lombok has
yellow-crested
cockatoos.

Only about 35
kilometres of
sea—and such a
different cast of
birds. Why?

Zoom out: orangutans
in Borneo. Tree
kangaroos in New
Guinea.

Why do the animals
change so
dramatically across
this island world?

Meet the Wallace
Line: a boundary in
animal
distributions, not a
wall in the water.

It passes between
Bali and Lombok,
then between Borneo
and Sulawesi.

Let me make that
boundary clearer—

Och. Wrong left
hand. That’s a new
coastline, not a
scientific
discovery.

From 1854 to 1862,
Alfred Russel
Wallace travelled
the Malay
Archipelago.

Local guides and
collecting
assistants helped
make that
extraordinary
fieldwork possible.

Wallace helped fund
his work by selling
specimens to
collectors.

Comparing animals
from island after
island made the
pattern hard to
ignore.

Crossing from Bali
to Lombok, he
noticed a striking
change in the birds.

By 1859, he had
described the faunal
boundary we now call
the Wallace Line.

In 1858, while ill,
Wallace also
independently worked
out natural
selection and sent
his ideas to Darwin.

Different
breakthrough, mind!
That explained
evolutionary
change—not the deep
geography behind
this line.

Wallace recognised
that past geography
mattered. Modern
geology added the
deeper history.

The answer starts
beneath the sea—not
with animals obeying
an invisible fence.

West: the Sunda
Shelf, linked to
Asia. Far east: the
Sahul Shelf, linking
Australia and New
Guinea.

Between them lies
Wallacea—including
Lombok and Sulawesi.
It is NOT simply the
Australian shelf.

Over tens of
millions of years,
Australia moved
north and interacted
with Southeast
Asia’s complex plate
boundaries.

Uplift, volcanic
arcs and shifting
seas built an island
maze between
long-separated
animal worlds.

During Ice Ages, sea
level fell by
roughly 120 metres,
exposing broad
continental shelves.

Land bridges
expanded Sunda and
Sahul. But they did
not turn Wallacea
into a continuous
road between
continents.

The Bali–Lombok
channel stayed wet
even when the sea
fell.

A shallow shelf can
become a bridge. A
deep channel remains
a moat.

I wanted the
measuring staff. Not
the drill. Aye, the
hand selection needs
work.

Depth and isolation
kept many land
animals from simply
walking across.

But birds can fly,
you say? Many forest
birds rarely cross
open water.

The sea is a
filter—not a perfect
seal. Some animals
do swim, fly or raft
across.

And reaching an
island is not
enough. You have to
survive and
reproduce there.

Climate tolerances
helped make exchange
uneven: many Asian
lineages were better
suited to humid
stepping-stone
habitats than
lineages from drier
Australia.

Sulawesi reveals the
messy, wonderful
truth: macaques with
Asian ancestry share
forests with bear
cuscuses—marsupials
with Australasian
roots.

Wallacea is a region
of selective mixing
and distinctive
evolution, not a
simple animal
switch.

A babirusa wears
curling tusks
through its snout. A
maleo lets warm
earth incubate its
buried eggs.

Not monsters
guarding a
border—unique lives
shaped by isolation,
arrivals and time.

I came looking for a
line. I found moving
continents, vanished
land bridges, deep
water—and the chance
journeys of living
things.

Aye. The wonder is
not that the wall is
invisible. It’s that
the world remembers.

The Earth always has
another story to
tell!

Now, which left hand
opens the biscuits?