In the animal kingdom,
intelligence has evolved in many different ways, in many different creatures.
We often think of our fellow primates at the top of the intelligence list
with their ability to use tools like sticks and rocks to access food
and with their ability to recognize themselves in the mirror.
Orcas too are among the most intelligent,
with their unique language skills and orchestrated hunting techniques.
And anyone with a dog is constantly surprised
at complex feats of social intelligence and emotional sensitivity.
Intelligence seems to thrive in animals like this –
mammals – often carnivorous ones –
that live in tight social groups.
But if we survey the world of animals,
one of the smartest is one that is perhaps unexpected,
an animal that isn’t a mammal at all,
but a bird – crows,
or more generally – corvids.
Corvids are mischievous, playful, and extremely intelligent.
They use tools to forage and to solve complex problems –
they even drop nuts on a road for cars to crack,
and then pick them up with the safety of pedestrian lights.
They can also recognize faces
and can hold a grudge against someone who was rude to them for several years.
They can mimic sounds that they hear,
and scientists have found that
their problem solving skills rival that of a 7-year-old human
How is it that crows are so profoundly intelligent,
and how is it that we even measure their intelligence in the first place?
Is bird intelligence wired in the same way as mammal intelligence,
or is it something different all together?
The corvid family is also known as the crow family,
and includes crows, jays, ravens, rooks, and magpies.
其中包括乌鸦 松鸦 渡鸦 秃鼻乌鸦和喜鹊
The level of intelligence varies between the species,
but scientists have found that the New Caledonian crow is the most intelligent,
they’re to corvids what we are to the rest of the primates.
the crows were presented with various tubes filled with water,
with a treat floating on top, which they couldn’t quite reach.
In one trial,
when presented with a treat inside a tube of water and a treat sitting on top of sand,
the crows knew to drop rocks into the water-filled tube
to raise the water level to reach the treat,
and ignored the tube with sand.
In the next trial,
when presented with a single tube of water, and objects with various densities,
the crows knew to select the sinking objects
rather than the floating ones to reach the treat.
When presented with two tubes of differing water levels,
the crows knew to drop objects into the tube with the higher water level
to reach the treat faster.
These trials demonstrated the crows’ abilities
in both problem solving and tool use.
And the authors believe that their skill level
at deciphering and completing these tasks
is similar to 5 to 7-year-old children.
However, in two more challenging tasks,
the crows didn’t perform as well.
One required understanding the difference in a wide tube versus a narrow tube,
and another was a counter-intuitive task
where the tube with the reward
was connected to another tube via a hidden u-bend,
the crows didn’t fully grasp these setups.
But in comparison, during tests with human children,
only kids around 8 years old were able to consistently solve such tests.
And in addition to using tools, New Caledonian crows can build tools,
and not just simple ones, but ones with multiple parts.
When given objects that were too short
to retrieve food from a puzzle box,
the crows combined elements
by inserting one stick into the hollowed opening of another
to make a tool long enough to reach the food.
One crow even made 3 and 4-part tools.
Compound tool construction like this
has only been observed outside humans
in a few captive great apes.
It is usually only associated with human intelligence.
And in addition to this, we now think
crows might be better than we ever could have imagined
at making plans for the future.
The ability to take actions now that will give a benefit later
is not something that most animals are good at.
Delayed gratification and planning are high-order skills.
Human children can’t do this,
and neither can’t many of the adults that I know.
It requires our memory of the past and foresight for future events.
Can crows, of all animals,
really possess this ability?
In a study published in 2020,
New Caledonian crows were first shown
one of three puzzle boxes that they already knew how to open
–each requiring a specific tool.
They were then removed from the test area for 5 minutes
before being presented with 5 different objects:
1 tool for each of the boxes, and 2 distraction objects.
After selecting an object and waiting 10 minutes,
they were allowed back into the test area.
The researchers discovered that
not only did the birds choose the correct tool
that would open the corresponding puzzle box,
but they would remember to bring the tool with them into the test area.
In another study,
researchers presented the birds
with a locked box with a treat in a similar manner.
But this time, the birds were then presented with an assortment of items
including the correct tool, a few distracter tools, and an immediate food reward –
but one that was less appealing than the one in the locked box.
And most of the time,
the birds took the risk and delayed their gratification,
kept the correct tool,
and later opened the box with the better treat.
This might seem easy to us, but it isn’t.
Only once human children reach 5 years old does this ability arise,
and even then, it doesn’t in all of them,
for some, it takes a few more years.
These mental skills certainly set crows apart from other animals,
with their actions and abilities more in line with the smartest of the primates.
How does this bird
give the most intelligent primates a run for their money?
Why does a bird need to be this smart?
Even though crows may have a similar intelligence to many primates,
bird brains and primate brains are not at all the same.
Birds and mammals split on the evolutionary tree
320 million years ago,
and since then, their brains have become quite distinct from one another,
making scientists question exactly why corvids are so smart.
In vertebrates, the pallium is the grey and white matter that covers the brain.
Before the evolutionary split,
both birds and mammals evolved a large pallium.
But, after their lineages split,
the mammal pallium evolved into a layered structure
known as the cerebral cortex.
This is the most complex structure of the mammalian brain.
Each layer contains nerve fibers running horizontally and vertically
that process and transmit information.
Here is where many important functions take place,
including learning, memory, sensory perception, and conceptual thinking.
包括学习 记忆 感官知觉和概念思维
Birds don’t have a cerebral cortex.
But a study published in 2020 found that
the fibers and circuitry in the bird pallium
are organized very similarly to a mammalian neocortex –
with fibers running both horizontally and vertically.
The authors believe this explains where bird intelligence comes from.
Another reason why birds were initially thought
to be incapable of this level of intelligence
was due to the small size of their brains.
But, it’s not the absolute size of an animal’s brain that matters,
but the brain-to-body ratio.
Crows tend to have big brains compared to their body size.
In mammals, the bigger-brained individuals are humans and dolphins;
in birds, it’s parrots and crows.
However, as scientists’ understanding of the brain grew,
they discovered it wasn’t just size that mattered,
or even brain size relative to body size.
A big proponent of an animal’s intelligence is the density of neurons.
This is because having tightly packed neurons
leads to better communication between them.
And it turns out
that certain bird species have very densely packed neurons.
In a 2016 study,
researchers measured the number of neurons in various bird and primate species.
They found that some birds, like corvids,
have twice as many neurons as primates
with similar-sized brains,
with numbers closer to that of larger primates.
While these findings tell us
how crows are so smart,
the question remains as to why.
Plenty of bird species thrive
with fewer neurons and weaker mental abilities,
so why did crows evolve this way?
One theory is that it has to do with the way they are raised.
Unlike other species,
corvids spend more time with their parents.
New Caledonian crows are fed by their parents for up to two years.
During this time,
they have ample access to role models who are making and using tools
and have the opportunity to use these tools themselves.
This extended parenting time allows skills to be transmitted vertically,
meaning, from parents to off-spring
The family groups of many species of crow can be very tight,
with young crows even helping to defend their parents’ new nest of babies.
However, beyond tight family groups,
adults of many species of corvids don’t lead particularly social lives.
New Caledonian crows mate for life,
but otherwise, don’t really interact with other adults.
Other species of corvid will often forage and roost in large groups,
or work together to mob a predator
– but there isn’t a social hierarchy or complex social bonds in these settings.
This seems to go against one leading theory of intelligence,
called the social intelligence hypothesis.
Chimpanzees, for example, live in large and complex social groups,
where they have to interact with others outside their immediate family
and keep tabs on many relationships.
It’s a constant game of politics.
Dogs, wolves, and even orcas,
狗 狼 甚至虎鲸
have to deal with a great amount of social complexity.
And this “social intelligence” needs a lot of brain power.
If adults of many of the smartest corvids
don’t live in complex social groups,
why would a similar intelligence have evolved?
Adult corvids may rarely live in wide social groups, but often, juveniles do.
Before pairing up with a mating partner, during their ‘teenage’ years,
some species of corvids live in larger flocks,
aptly called juvenile gangs.
And these gangs work exactly like it sounds,
a bunch of teenagers hang out and bully each other and fight.
In these angsty years, corvids, like ravens for example,
在这段焦虑的日子里 鸦科鸟类 如渡鸦
form the many relationships that they have to keep tabs on.
And, intriguingly, corvids may need social intelligence
to interact with other species.
Outside of Yellowstone National park,
certain ravens have been seen interacting with wolves – especially wolf pups.
The animals can be seen to play tug-of-war,
and the ravens teasing and enticing the puppies to jump and grab sticks.
Sometimes, the ravens will even pull the wolves’ tails.
By all accounts, it looks like the animals are playing.
Some scientists think that
individual ravens may even develop special bonds with individual wolves within a pack.
may help the ravens more readily scavenge the wolves’ kills.
This propensity to interact with other species
has some groups wondering
how we may be able to cooperate with corvids.
One idea is to train crows and other corvids
to pick up cigarette butts or garbage.
A few different companies are developing devices that will autonomously train the birds,
giving the birds a treat once they place the trash into the device.
A theme park in France has already been undertaking a similar operation.
They trained six rooks to pick up trash, four days a week,
under the supervision of the park’s falconer.
While it may seem like
we’re taking advantage of these birds and their intelligence
by having them do something we should already be doing ourselves,
those involved seem to have good intentions.
It helps the environment,
teaches humans to cooperate with other species,
and teaches the public about these intelligent creatures.
By studying other intelligent species,
and what made them that way,
scientists have gained a better understanding of the brain and its development.
And for all we know,
we could be overlooking other small-brained species
that could harbor a higher intelligence
– other animals that can help us unlock the many secrets of the brain.
I love talking about animal intelligence on this channel,
because I love the way the brain works.
I love its mysteries and its unbelievable power.
And because of this I love the feeling of learning
– of grasping new concepts,
of those moments of sudden understanding washing over you,
喜欢当物理 数学 化学和生物开始串连起来时
when physics and math and chemistry and biology start to click together,
feeling like one beautiful interconnected machine
that explains our universe.
I’d like to think crows feel this too
when they get their treat out of the tube.
To engage myself in STEM learning, I use Brilliant.
And if you’re looking for something else to watch right now,
you can watch our previous video about the jellyfish that lives forever,
or watch Real Engineering’s latest video
about the way engineering solved the mystery of the Concorde crash.
In the animal kingdom,