Every minute you spend awake, your mind passes from experience to experience.
From the unique taste of your favourite food, to a cherished childhood memory,
to that sudden fear that you may have left the stove on.
This ebb and flow of thoughts and feelings
is often described as our stream of consciousness.
And in the past, this experience was believed to be uniquely human.
However, over the past few years, ingenious experiments have provided
compelling evidence that many animals do have a conscious experience.
Some species, including certain species of apes, crows and cuttlefish,
even seem capable of quite complex thought processes,
such as planning for the future. A cuttlefish,
for example, will eat less shrimp if it expects to find a tastier crab later on.
But when did this ability to think and feel evolve and why?
Well, an exciting new theory from Ava Jablonka at Tel Aviv University
and Simona Ginsburg at the Open University of Israel
hinges around a process called unlimited associative learning.
Put simply, this is the capacity to remember the link between a cue
and an event, even if time has passed between them,
and to update expectations of future rewards or punishments
according to the changing environment.
For example, a spider monkey might learn
that a red fruit has a sweet taste, while a green one tastes bitter.
It can also learn that if it picks the fruit when alone, it can eat it safely.
But if a more dominant individual is around, it may be better to run away.
But what's important is that it has the ability to form many of these links.
This is the reason it's called unlimited associative learning.
The benefits of this ability are huge
since it allows creatures to build flexible behaviours
that would help it to survive and thrive.
For example, unlimited associative learning helps animals to respond
to changing environments and to explore new territories.
And this helps explain why consciousness evolved,
because according to Jablonka and Ginsburg,
unlimited associative learning is only possible if you possess
all the abilities associated with consciousness, abilities such
as: feeling rudimentary emotions, like reward and pain;
paying attention to particular sensory stimuli
while ignoring others; and having a basic sense of self.
By comparing which animals demonstrate unlimited associative learning today,
it is also possible to trace back through the evolutionary tree
to guess which of our ancestors first evolved
this ability and, therefore, when consciousness first evolved on Earth.
The research to date suggests that consciousness evolved three times.
In early fish-like vertebrates more than 500 million years ago;
in a common ancestor of arthropods, such as insects, spiders
and crustaceans, at around the same time;
and then in the cephalopod molluscs
around 300 million years ago.
Once consciousness had emerged, the capacity
for more complex behaviours created an arms race between competing species.
Predators would have been better at finding prey, which would have meant
that the animals on the bottom of the food chain,
in turn, needed to evolve ways to avoid detection.
This arms race helped drive the Cambrian Explosion,
the explosion of new species around 500 million years ago,
sometimes described as evolution's 'big bang moment'.
Over time, the emergence of animals' inner lives
would change our outer world.
A plant that evolved
attention-grabbing flowers would attract a higher number
of pollinating insects. If insects were not conscious,
these amazing floral displays may never have evolved.
It is awe-inspiring to think of these turning points
in evolutionary history – when the Earth, previously unobserved by any being,
started teeming with creatures that could not only observe it,
but appreciate its endless wonders.