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Innate behaviors

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Learn about behaviors that are pre-programmed into an animal's genes, including reflexes and fixed action patterns.

Key points

  • Innate behavior is behavior that's genetically hardwired in an organism and can be performed in response to a cue without prior experience.
  • Reflex actions, such as the knee-jerk reflex tested by doctors and the sucking reflex of human infants, are very simple innate behaviors.
  • Some organisms perform innate kinesis, undirected change in movement, and taxis, directed change in movement, behaviors in response to stimuli.
  • Fixed action patterns consist of a series of actions triggered by a key stimulus. The pattern will go to completion even if the stimulus is removed.
  • Scientists can test if a behavior is innate by providing a stimulus to naive—untrained—animals and to see if the behavior is automatically triggered.

Introduction

If you watch a herring gull caring for its chicks, you may notice a funny ritual around feeding time. The parent gull has a red spot on its beak. When it taps its beak on the ground, the chick will peck at the spot several times.
This pecking triggers a response in the parent: it throws up food for the chick.start superscript, 1, end superscript That may sound gross to us, but to a herring gull chick, it's like a pizza dinner!
The tapping behavior is innate, or genetically preprogrammed. Herring gull chicks will peck at the red dots of their parents' beaks without any prior training. In fact, a baby herring gull can be tricked by a yellow stick adorned with a red dot—it will peck at the stick just as eagerly as it would at a parent's beak.squared
This is just one example of an innate behavior, or behavior that's genetically hardwired in an organism. Given the right cues, an organism will perform an innate behavior without the need for prior experience or learning. Innate behaviors tend to be very predictable—like the herring gull tapping—and they are often performed in a very similar way by all members of a species.
In this article, we'll see examples of behaviors that are largely or fully innate. Keep in mind, though, that many behaviors in the real world are partly innate and partly learned. Zebra finches, for example, are preprogrammed to learn a song, but which song they learn depends on their early experience.

Reflexes

Perhaps the simplest example of an innate behavior is a reflex action: an involuntary and rapid response to a stimulus, or cue.
One example of a human reflex action is the knee-jerk reflex. To test this reflex, a doctor taps the tendon below your kneecap with a rubber hammer. The tap activates nearby neurons, causing your lower leg to kick involuntarily. This automatic response depends on circuits of neurons that run between the knee and the spinal cord—it doesn't even involve your brain!
Some reflexes are present in human babies but are lost or placed under conscious control as the baby grows older. For instance, a newborn baby will suck at anything that touches the roof of its mouth.cubed This reflex helps the baby get food by ensuring it will suck at its mother's breast or a bottle placed in its mouth.
Image credit: Baby bottle by Dirk (Beeki) Schumacher, public domain

Kinesis and taxis

Some organisms have innate behaviors in which they change their movement in response to a stimulus, such as high temperature or a tasty food source.
In kinesis, an organism changes its movement in a non-directional way—e.g., speeding up or slowing down—in response to a cue. For example, woodlice move faster in response to temperatures that are higher or lower than their preferred range. The movement is random, but the higher speed increases the chances that the woodlouse will make its way out of the bad environment.
Image credit: Common rough woodlouse by JMK, CC BY-SA 3.0
Taxis is a form of movement behavior that involves movement towards or away from a stimulus. This movement can be in response to light, known as phototaxis; chemical signals, known as chemotaxis; or gravity, known as geotaxis—among other stimuli. It can also be directed towards, positive, or away from, negative, the source of the stimulus.
For example, woodlice show negative phototaxis, meaning that they'll move away from a light source.start superscript, 4, end superscript This behavior may be helpful because woodlice require a moist environment, and a sunny, light, spot is more likely to be warm and dry.

Fixed action patterns

A fixed action pattern is a predictable series of actions triggered by a cue, sometimes called the key stimulus. Though a fixed action pattern is more complex than a reflex, it's still automatic and involuntary. Once triggered, it will go on to completion, even if the key stimulus is removed in the meantime.
We already saw one example of a fixed action pattern in the introduction of the article: spot-pecking behavior in herring gulls. Let's look at a couple other examples that show how fixed action patterns work.

Case study: egg retrieval

A well-studied example of a fixed action pattern occurs in ground-nesting water birds, like greylag geese. If a female greylag goose's egg rolls out of her nest, she will instinctively use her bill to push the egg back into the nest in a series of very stereotyped, predictable, movements. The sight of an egg outside the nest is the stimulus that triggers the retrieval behavior.
It's not too hard to imagine why this hardwired trait would be favored by natural selection. Goose mothers that retrieve their lost eggs are likely to have more surviving offspring, on average, than those that don't.
Image credits: left, Greylag goose by David Iliff, CC BY-SA 3.0; right, Goose nest on Fadamull by Gordon Hatton, CC BY-SA 2.0
However, this fixed action pattern can also occur under circumstances where it is not useful, in other words, where it does not benefit the goose:
  • If the egg that rolls out of the nest is picked up and taken away, the goose will keep moving her head as though pushing an imaginary egg.
  • The goose will try to push any egg-shaped object, such as a golf ball, if it is placed near the nest. In fact, she'll even carry out the retrieval pattern in response to a much larger object, such as a volleyball!
This example illustrates the fixed aspect of a fixed action pattern. In the great majority of cases a goose is likely to encounter in nature, the behavior of rolling any egg-like object near the nest back into the nest will be beneficial. However, it's simply a biological program that runs in response to a stimulus and can have unhelpful results under unusual circumstances.

Case study: male sticklebacks

Another classic example of a fixed action pattern comes from the three-spined stickleback, a small freshwater fish. During the breeding season, male sticklebacks develop a red belly and display innate aggressive behavior towards other males.
When a male stickleback spots another nearby male, he will launch into a fixed action pattern involving aggressive displays designed to scare off the stranger. The specific stimulus that triggers this fixed action pattern is the red belly coloration pattern characteristic of males during breeding season.
How do we know that this is the trigger? In the lab, researchers exposed male fish to objects that were painted red on their lower halves but didn't otherwise look like a fish, see below. The male sticklebacks responded aggressively to the objects just as if they were male sticklebacks. In contrast, no response was triggered by lifelike male stickleback models that were painted white.start superscript, 5, end superscript
Image credit: Behavioral biology: Figure 1 by OpenStax College, Biology, CC BY 4.0
By some accounts, this fixed action pattern has even been triggered by a fire truck driving past a male stickleback's tank!start superscript, 6, end superscript

How do we know if a behavior is innate?

By definition, an innate behavior is genetically built in to an organism rather than learned. But how do biologists figure out if a behavior is innate?
In general, scientists test whether a behavior is innate by seeing whether it is performed correctly by naive animals, animals that have not had a chance to learn the behavior by experience. For instance, this might involve raising young animals separate from adults or without stimuli that trigger the behavior.
As an example, let's consider digging behavior in the deer mouse and the beach mouse. These species are closely related and can interbreed, but they live in different natural environments and have different burrow-digging behaviors:start superscript, 7, end superscript
  • The deer mouse digs a small, short burrow.
  • The beach mouse digs a long burrow with an escape tunnel or "back door" to get away from predators.
Image credits: left upper panel, Captive bred Peromyscus maniculatus by 6th Happiness, CC BY-SA 3.0; right upper panel, Alabama beach mouse (Peromyscus polionotus ammobates) by Jackie Isaacs/USFWS, public domain; burrow diagrams based on Weber et al.start superscript, 8, end superscript, Figure S1
Is this difference in burrow digging innate? To ask this question, researchers raised mice of both species in the lab with no exposure to sand or opportunity to burrow. Then, they provided them with sand, a cue for burrow construction.
Given sand, each naive mouse dug exactly the type of burrow made by its species in the wildstart superscript, 9, end superscript. That is, beach mice dug a long burrow with an escape tunnel, while deer mice dug a short burrow without an escape tunnel. The ability of the mice to construct their normal tunnels, without ever having seen such a tunnel before, showed that the burrowing behavior was indeed innate.

Check your understanding

Which of the following best describes a fixed action pattern?
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