Evolution of the Brain

Created for SPICE by Catherine Marcinkiewcz and Sean Sand

How did the Brain Evolve?

Homeobox genes – genes that control the development of different segments of the body (and brain)

From fly to human – homeobox genes (“hox” genes) are very similar

During evolution, some of these genes have been duplicated to give rise to homologous structures

This is how the hindbrain emerged from the spinal cord, the midbrain from the hindbrain, the forebrain from the midbrain, and so on

Our Brainy Predecessors

Worms and bugs

Worms can learn, too

Worms are the simplest organisms to have a central nervous system

Roundworms learn by sense of smell and will avoid “bad” bacteria that make them sick

“Shocking worms”: Can they learn to avoid the shock?

Planaria “flatworms” learn to avoid the side where shock was administered

Zhang, et al, Nature 438 Nov.10 2005

Without a head Different parts of the worm nervous

system can function independent of the brain

Can perform many types of behaviors including locomotion, mating, feeding, even maze learning without the brain

Some worms can even regrow a head or grow two heads if the brain is bisected

Insect Brains Increasing complexity of brain and nervous system Giant fiber systems allow rapid communication

between brain and muscles (precursor to spinal cord) The head region is dominant, and the body cannot

survive without the head (unlike worms)

Honeybees use olfactory cues to locate nectar sources

Forms olfactory “memories” which can be used to find nectar in the future

Language? Back at the hive, they perform a waggle dance that tells other bees where to find the nectar

The Vertebrate Brain

Fish, reptiles, birds and mammals

Cortical Expansion

The Forebrain – evolved in vertebrates as an outgrowth or extension of the brain stem

In mammals, the “neocortex” is basically an enlargement of the forebrain

In humans and other primates, the neocortex is so large that it completely covers the brain stem

Rat

Lizard

Cat Monkey

Human

Brain Organization

The vertebrate brain has 3 basic components Hindbrain – most of the brainstem and the cerebellum. The

oldest and so-called “reptilian” brain because it is especially prominent in reptiles

Midbrain – part of the brainstem that evolved most recently Forebrain – the limbic system and the cerebral cortex

Alien Intelligence

Octopus and Squid

The Cephalopod Brain Cephalopods are the only

invertebrates with intelligence similar to mammals

“Convergent evolution”

Long and short-term memory Most behaviors are learned

rather than instinct-based “Play” activity Escape artists

The mimic octopus: An octopus with Tourette’s

A Different Kind of Brain

Tentacles can operate independent of the brain (i.e. they are autonomous)

Not all sensory information is centrally processed

Suction cups can feel and taste food simultaneously

Poor proprioception (unlike mammals) No stereognosis – the ability to form a mental

image of the object it is holding