Taste, also known as gustation, is one of the traditional five senses. It allows animals to detect flavors in potential foods and other substances. Taste helps animals determine whether something is nutritious, toxic, or otherwise worth ingesting. Most animals have some ability to detect at least sweet, sour, salty, and bitter tastes. However, there is debate around whether any animals entirely lack a sense of taste.
Do all animals have taste buds?
Most animals have taste receptor cells, known as taste buds, that allow them to detect different flavors. Taste buds contain taste receptor cells that connect to nerves that transmit taste information to the brain.
Mammals, birds, reptiles, amphibians, fish, and even invertebrates like mollusks and insects have taste buds and a sense of taste. Their taste abilities range from simple detection of sweet and bitter to complex identification of multiple flavor profiles.
However, some animal species do appear to lack typical taste buds and a major sense of taste. The question is whether they have zero taste ability or some minimal ability to detect basic flavors like sweet and bitter.
Do any animals completely lack taste?
Very few animals are believed to totally lack a sense of taste. However, there are some species that appear to have little to no ability to detect flavors:
– Sea Stars – Sea stars and other echinoderms do not have a centralized brain or distinct sensory organs. They have a primitive nervous system but appear to completely lack taste buds or taste reception abilities.
– Jellyfish – Like sea stars, jellyfish do not have a brain or sensory receptors associated with smell or taste. Their simple nervous system allows them to respond to touch, light, and chemical signals but they are not believed to taste.
– Sea Urchins – While sea urchins have primitive chemoreceptors for smell, there is no evidence that they can detect tastes. Like related echinoderms, they lack taste buds.
– Corals – Corals are very simple animals related to jellyfish. They have a basic nerve net that coordinates their activities but do not have sensory cells or abilities related to smell or taste.
So while most animals have taste, a few very primitive marine invertebrates may be naturally “taste-blind”. However, there is still debate around whether they have some minimal taste reception. Next we’ll look at their limited chemosensing abilities.
Primitive taste abilities in taste-blind animals
While the animals listed above appear to completely lack taste buds, that doesn’t necessarily mean they have no ability to detect chemicals in their mouths. Primitive chemoreceptors may allow for minimal taste-like function.
For example, sea stars use their tube feet to detect and move toward food sources. Although they do not have taste buds, they clearly have some chemical sensing ability that guides them toward edible substances. So they do not have taste in the traditional sense but do have primitive taste-like chemosensing.
Similarly, sea urchins, jellyfish, and corals have simple nerve nets that detect and respond to chemical stimuli, even if they do not form a full sense of taste. Their systems allow them to move toward potential food.
Benefits of lacking taste
For simple marine animals living in the ocean, lacking a sense of taste may offer advantages:
– They can detect and consume wider array of foods – Unlike animals that use taste to avoid toxins or select for nutrients, these primitive species can eat anything digestible without limiting themselves.
– Reduces need for complex sensory processing – Sensing only basic stimuli like light and touch allows them to have simpler nervous systems. They avoid the cost and complexity of processing taste information.
– Avoids deterrence by toxins – Many plant and animal chemical defenses target the sense of taste. Without taste, these toxins have limited effects as deterrents for these species.
So while taste gives many animals cues about what to eat and avoid, for some very simple species it may be an unneeded sensory ability and potential liability. Their primitive chemical sensing fulfills their core needs without the cost and complexity of full taste reception and processing.
Could taste be detected in other ways?
Since the taste-blind animals discussed have some ability to detect and respond to chemicals, it raises the question of whether they have an alternative system that approximates taste:
– Internal chemoreceptors – In addition to external taste buds, some animals have internal chemoreceptors in their digestive tracts that detect the chemical composition of food as it is ingested and digested. Animals like sea stars may depend more on these internal taste mechanisms.
– Smell providing taste-like information – With no taste buds, these animals may still get some taste-related information from smell chemicals wafting from food sources. Smell would not provide the full experience but could provide limited input.
– Individual cells detecting key taste stimuli – Even if there are no structured taste buds, some isolated cells spread over the body surface may be able to detect sweet or bitter compounds providing a minimalist taste ability.
– Incidental absorption through skin – Some taste chemicals may be incidentally absorbed through the skin/outer surface, again giving minimal cues about food edibility.
So while these animals clearly do not have a complete sense of taste, they may have some limited substitute systems that provide a coarser version of taste input based on chemicals.
Could any animals evolve to lose taste ability?
Since a few primitive marine animals appear to function fine without true taste, could this ability be lost in other species through evolution? There are a few possibilities:
– Aquatic predators – Sharks, marine reptiles like sea turtles, and fish-eating whales could potentially evolve reduced taste if they are getting by on smell and vision to find prey. Relying on those other senses could allow taste to fade as unnecessary.
– Narrow diet specialists – Animals that specialize in eating just one or two difficult to digest foods, like leaf-eating koalas, may benefit from losing deterring taste receptors and focusing digestion narrowly on those foods.
– Parasites – Parasites that live on or in a host and take up food from it could lose external taste receptors and rely on internal digestion of whatever the host ate. Eventually taste might fade away.
– Carrion specialists – Animals specializing in scavenging like vultures or crabs may benefit from an expanded palate and loss of taste-driven deterrence if they focus solely on smell to find carrion.
However, full loss of taste is unlikely in most animals. Scent, vision, touch provide limited taste-like information, so maintaining at least some basic taste reception provides an advantage that would prevent it from being selected against. But in specialized niche cases, taste could be sacrificed.
Could we eliminate taste artificially?
While natural evolution of taste loss is unlikely, emerging biotechnologies raise the question of whether we could engineer taste-blind animals. Genetic manipulation or gene editing techniques like CRISPR open this possibility:
– Delete taste bud development – Deleting the genetic instructions that neurons need to form taste buds and receptors could prevent their formation entirely.
– Disable taste signal transmission – Removing genes for taste receptor proteins or enzymes that transmit taste signals could create signaling dead ends.
– Overexpress taste inhibitors – Enhancing production of signaling inhibitors for taste pathways could overwhelm taste response.
– Replace taste genes with non-functioning versions – Direct replacement of taste related genes with nonfunctional copies through gene editing could break taste systems.
However, biotechnologically removing taste would be ethically questionable and provide no clear benefit. But it does demonstrate that we likely have the tools to produce taste-blind animals. Natural evolution has led to a few tasteless species, and we could mimic that in the lab.
Do humans lack some taste abilities?
Unlike other animals, there are some taste differences between humans, in addition to preferences:
|More taste buds
|Heightened taste response
|Fewer taste buds
|Reduced taste response
|Specific taste blindness
|Inability to detect some flavors
So while humans do not show total taste loss, differences in genetics, taste bud density, and specific taste receptors lead to variation in our taste experiences.
The sense of taste provides valuable information to most animals about the foods they eat. Only a very few primitive marine species like sea stars and sea urchins appear to completely lack taste buds and specific taste abilities. However, they have some minimal capacity to detect chemicals using primitive nervous systems. While total taste loss is rare in nature, biotechnologies raise the possibility that we could someday engineer taste-blind animals. Humans also show natural variation in specific taste abilities based on genetics. Overall, the sense of taste is nearly universal across the animal kingdom, though diminished in some primitive species.