Why are some animals so much more intelligent than others?

Why are some animals so much more intelligent than others?

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From what I found many biologists state that animals living in large social groups (elephants, primates, cetaceans etc.) have a tendency for improved cognitive abilities. Yet at the same time there are solitary animals with (suspected) high intelligence such as octopuses and plenty of social animals that fail our cognition tests.

What evolutionary pressures pushed certain animals towards such intelligence when their environments are so different while other animals in a similar environment show no exceptional cognitive skills?

How smart are killer whales? Orcas have 2nd-biggest brains of all marine mammals

Killer whales. Image: NOAA

Neuroscientist Lori Marino and a team of researchers explored the brain of a dead killer whale with an MRI and found an astounding potential for intelligence.

Killer whales, or orcas, have the second-biggest brains among all ocean mammals, weighing as much as 15 pounds. It's not clear whether they are as well-endowed with memory cells as humans, but scientists have found they are amazingly well-wired for sensing and analyzing their watery, three-dimensional environment.

Scientists are trying to better understand how killer whales are able to learn local dialects, teach one another specialized methods of hunting and pass on behaviors that can persist for generations -- longer possibly than seen with any other species except humans.

These researchers have yet to find evidence that an orca in the wild has ever killed a person. But they aren't surprised that the world's biggest, most powerful and possibly smartest predator, captured and kept for years in a tank, cut off from the influences of an extended family, could have a fatal encounter with a human.

Human interaction with captive killer whales has come under scrutiny since Feb. 24, when a large male orca with a checkered past killed a trainer at SeaWorld Orlando by dragging her into a tank.

"I'm not trying to second-guess what was in this particular whale's mind," said Marino, part of the Neuroscience and Behavioral Biology Program at Emory University in Atlanta. "But, certainly, if we are talking about whether killer whales have the wherewithal and the cognitive capacity to intentionally strike out at someone, or to be angry, or to really know what they are doing, I would have to say the answer is yes."

Years of tediously difficult research has given scientists some understanding of killer whales -- but also has made them aware of how little they know about the creatures.

For starters, there's puzzlement over exactly how to categorize them.

They swim the world's oceans -- they are more widely distributed than any whale, dolphin or porpoise -- in at least three distinct populations. There are fish-eating orcas that stay in one area, flesh-eaters that wander more widely along coasts, and a third group that roams the deep-blue waters.

The three groups have starkly different diets, languages, hunting techniques and manners of behaving around other marine life, and they don't seem to interact much with one another.

"If they didn't have the same paint jobs, you'd call them different species," said Brad Hanson, a National Oceanic and Atmospheric Administration biologist in Seattle.

Yet the orcas' DNA tells a different story. Instead of the world's varied populations having genetics that spread outward like a tree with several main branches, theirs is but a single, nearly straight trunk, except for a mismatched pair of genes here and there.

"It's very, very strange," said Hanson, who participated in research that led to the listing of resident whales in waters off the Northwestern U.S. as endangered.

If genetic variety isn't what makes these killer-whale groups so different, scientists suspect, their enormous brains might be the telltale factor.

Bigger animals typically have bigger masses of brain cells. But scientists use brain-weight-to-body-weight ratios as a rough measure of intelligence. By that measure, human brains, by comparison, are seven times average. Orcas' brains are 2 1/2 times average -- similar to those of chimpanzees.

But scientist think that looking just at the brain-body ratio seriously underestimates the thinking power of larger marine mammals. In other words, orcas might be even much smarter than the size of their big brain suggests.

Hal Whitehead, a biology professor at Dalhousie University in Nova Scotia, awakened the world of cetacean research in 2001 when he co-authored a controversial paper that suggested no species other than humans are as "cultural" as orcas.

"Culture is about learning from others," Whitehead said. "A cultural species starts behaving differently than a species where everything is determined genetically."

One example of a killer-whale culture, he said, is the teaching of a particularly difficult and dangerous hunting technique observed by researchers on Antarctic islands. They watched as mothers repeatedly pushed their young onto beaches in pursuit of seals and sometimes had to drag their stranded young back into the water.

"They have their way of doing things, which they've learned from their mother and their other relatives," Whitehead said.

"Killer whales also are quite conservative animals," he added. "If this is the way they do things, then they are quite loath to do it another way."

That last point, he said, is important to consider when it comes to orcas held in captivity.

"That's pretty tough for any cultural animal, especially one from a conservative culture," Whitehead said.

Equally remarkable to researchers is the orca's ability to communicate with whistles and pulsed calls, and to "see" by making a clicking sound that works like sonar.

Many cetaceans -- whales, dolphins and porpoises included -- have these abilities to some degree. But orcas learn local and complex languages that are retained for many generations. And their bio-sonar, or echolocation, abilities also amaze researchers.

Professor Whitlow Au, of the University of Hawaii's Marine Mammal Research Program, finished a study recently adding to evidence that orcas can use their bio-sonar not just to find fish in murky water and not just to single out salmon, but to identify their favorite meal: Chinook salmon.

"They can recognize Chinook salmon from a long ways away," said Au, who put the distance at roughly half a football field. "They are able to use their bio-sonar to detect and track and eventually catch them."

Sam Ridgway, a neurobiologist and research veterinarian at San Diego's National Marine Mammal Foundation, which works for the Navy, said the orca brain has a relatively smaller amount of cerebral cortex -- the gray matter involved in memory, attention and thought -- than the human brain does. But it has large-diameter myelinated axons, which carry nerve impulses.

"It's analogous to a computer that has maybe less memory but bigger wires," said Ridgway, who puts a high value on being able to work with orcas in captivity. "The bigger the axon, the faster the nerve impulses travel."

Patrick Hof, vice chairman of the Department of Neuroscience at New York's Mount Sinai School of Medicine, summed up the orca noodle as a "big brain, a really big brain" with enormous capacity.

But whether that capacity creates the potential for intentionally killing a human is something for which there is "no scientific knowledge to prove," he said.

"It's a wild animal to begin with, and it has predatory behaviors that are well-known," Hof said. "It is possible that, in a situation of stress or captivity or stress related to captivity, some of the natural behavior might be expressed."

Marino, the Emory neuroscientist, wonders about the extent to which a captive orca could grow frustrated with being cut off from the cultural richness of living among an extended family -- grandparents through calves -- and the environmental richness of swimming the world's oceans.

"Living in a tank and having to splash people with your tail every day for 27 years would make anyone go nuts," Marino said.

(c) 2010, The Orlando Sentinel (Fla.).
Distributed by McClatchy-Tribune Information Services.

DNA Discoverer: Blacks Less Intelligent Than Whites

One of the world's most eminent scientists has created a racial firestorm in Britain.

James D. Watson, 79, co-discoverer of the DNA helix and winner of the 1962 Nobel Prize in medicine, told the Sunday Times of London that he was "inherently gloomy about the prospect of Africa" because "all our social policies are based on the fact that their intelligence is the same as ours — whereas all the testing says not really."

He recognized that the prevailing belief was that all human groups are equal, but that "people who have to deal with black employees find this not true."

Acknowledging that the issue was a "hot potato," the lifelong Democrat and avowed secular humanist nonetheless said his beliefs were not an excuse to discriminate against blacks.

"There are many people of color who are very talented," said Watson, "but don't promote them when they haven't succeeded at the lower level."

He told the interviewer, a former student of his, that he had recently inaugurated a DNA learning center near Harlem, and would like to have more black researchers at his lab, "but there's no one to recruit."

Steven Rose, a professor of biological sciences at the Open University in Britain, was quick to dismiss Watson's comments.

"This is Watson at his most scandalous, " Rose told the Times of London. "If he knew the literature in the subject, he would know he was out of his depth scientifically, quite apart from socially and politically."

Watson is the former director and current chancellor of the Cold Spring Harbor Laboratory biological-research institution on New York's Long Island, and both admired and infamous for bluntly speaking his mind.

In a British television documentary in 2003, Watson advised eliminating low intelligence through gene therapy.

"If you are really stupid, I would call that a disease," said Watson, according to New Scientist magazine. "The lower 10 percent who really have difficulty, even in elementary school, what's the cause of it?

"A lot of people would like to say, 'Well, poverty, things like that.' It probably isn't," he added. "So I'd like to get rid of that, to help the lower 10 percent."

He also touched upon sexual attraction in the same TV program.

"People say it would be terrible if we made all girls pretty," Watson said. "I think it would be great."

In 2000, he told a lecture audience at U.C. Berkeley that there was a correlation between a population's exposure to sunlight and its sex drive.

"That's why you have Latin lovers," Watson said, according to the San Francisco Chronicle. "You've never heard of an English lover. Only an English patient."

The notion that intelligence tests and other scientific evidence shows that racial groups differ in intelligence, at least statistically, is not a new one.

It last gained popular attention in 1994 with "The Bell Curve," a best-selling book written by Harvard psychologist Richard J. Herrnstein (who died before publication) and political scientist Charles Murray, which argued that intelligence was more important than socio-economic background or education in achieving success in American life.

The book does not explicitly ascribe a genetic, racial connection to intelligence, but Murray in his publicity tour to promote the book cited studies that human intelligence could be ranked by ancestry, with East Asians and European Jews leading the way.

That view was more clearly stated in 1995 by British-Canadian psychologist J. Philippe Rushton, whose "Race, Evolution and Behavior: A Life History Perspective" quantified dozens of differences between blacks, whites and Asians.

In the 1970s, electronics pioneer William Shockley, who won the 1956 Nobel Prize in physics, said that the human race would suffer as less intelligent people outbred more intelligent ones, with the greatest damage to occur in the black American population.

Most sociologists, geneticists and psychologists reject the notion of racial differences in intelligence, pointing out that economic and social factors clearly influence IQ test scores.

The issue of race itself is scientifically controversial, with some arguing that it is a meaningless term and others saying that consistent traits occur among individuals of shared ancestry.

Watson is currently in Britain promoting his just-published new volume of memoirs, "Avoid Boring People: Lessons From a Life in Science."

"There is no firm reason to anticipate that the intellectual capacities of peoples geographically separated in their evolution should prove to have evolved identically," he writes. "Our wanting to reserve equal powers of reason as some universal heritage of humanity will not be enough to make it so."


The DNA of today’s domesticated animals reveals that each species separated from its wild counterpart between 15,000 and 5,000 years ago, in the late Palaeolithic and Neolithic periods. Yes, this was also when we started breeding livestock. But it is not easy to see how this could have been achieved if those first dogs, cats, cattle and pigs were treated as mere commodities.

If this were so, the technologies available would have been inadequate to prevent unwanted interbreeding of domestic and wild stock, which in the early stages would have had ready access to one another, endlessly diluting the genes for “tameness” and thus slowing further domestication to a crawl – or even reversing it. Also, periods of famine would also have encouraged the slaughter of the breeding stock, locally wiping out the “tame” genes entirely.

But if at least some of these early domestic animals had been treated as pets, physical containment within human habitations would have prevented wild males from having their way with domesticated females special social status, as afforded to some extant hunter-gatherer pets, would have inhibited their consumption as food. Kept isolated in these ways, the new semi-domesticated animals would have been able to evolve away from their ancestors’ wild ways, and become the pliable beasts we know today.

The pug – a long way removed from its ancestors. Penguin , Author provided

The very same genes which today predispose some people to take on their first cat or dog would have spread among those early farmers. Groups which included people with empathy for animals and an understanding of animal husbandry would have flourished at the expense of those without, who would have had to continue to rely on hunting to obtain meat. Why doesn’t everyone feel the same way? Probably because at some point in history the alternative strategies of stealing domestic animals or enslaving their human carers became viable.

There’s a final twist to this story: recent studies have shown that affection for pets goes hand-in-hand with concern for the natural world. It seems that people can be roughly divided into those that feel little affinity for animals or the environment, and those who are predisposed to delight in both, adopting pet-keeping as one of the few available outlets in today’s urbanised society.

As such, pets may help us to reconnect with the world of nature from which we evolved.

Humans are not smarter than animals - we just don't understand them

For many years, humans have believed we are the most intelligent beings on the planet. However, evolutionary biologists are now claiming that some members of the animal kingdom may in fact have superior brains - we just don't recognise their intelligence.

Scientists at the University of Adelaide argue that evidence is emerging to suggest some animals actually have cognitive faculties that are superior to those possessed by human beings.

“For millennia, all kinds of authorities – from religion to eminent scholars – have been repeating the same idea ad nauseam, that humans are exceptional by virtue and that they are the smartest in the animal kingdom,” says Dr Arthur Saniotis, Visiting Research Fellow with the University's School of Medical Sciences.

"The belief of human cognitive superiority became entrenched in human philosophy and sciences. Even Aristotle, probably the most influential of all thinkers, argued that humans were superior to other animals due to our exclusive ability to reason.

“However, science tells us that animals can have cognitive faculties that are superior to human beings.”

Dr Saniotis said although animal rights began rising to prominence in the 19th century, the Industrial Revolution may have forestalled any gains made in our awareness of other animals.

Professor Maciej Henneberg, a professor of anthropological and comparative anatomy from the School of Medical Sciences, highlighted the different abilities of animals that are misunderstood by humans.

Animals are just as clever as us

1 /7 Animals are just as clever as us

Animals are just as clever as us

Cats. They're clever and they're coming to rule the world.

Animals are just as clever as us

They wait until we aren't watching.. then bam. Walking just like us

Animals are just as clever as us

This dog clearly understands the ɼheerleader effect'

Animals are just as clever as us

I want to thank my agent, my family, my owner..

Animals are just as clever as us

I think it is very clear this horse is cleverer than its humans. It knows it too.

Animals are just as clever as us

This cat works for the NSA. *probably

Animals are just as clever as us

There's always one.

He said: “Many quadrupeds leave complex olfactory marks in their environment, and some, like koalas, have special pectoral glands for scent marking. Humans, with their limited sense of smell, can't even gauge the complexity of messages contained in olfactory markings, which may be as rich in information as the visual world.

"The fact that they may not understand us, while we do not understand them, does not mean our 'intelligences' are at different levels, they are just of different kinds. When a foreigner tries to communicate with us using an imperfect, broken, version of our language, our impression is that they are not very intelligent. But the reality is quite different," Professor Henneberg says.

Prof Henneberg said another factor contributing to our belief was our fixation of technology and language, which have caused us to under-rate the different intelligences held by animals. "These include social and kinaesthetic intelligence. Some mammals, like gibbons, can produce a large number of varied sounds - over 20 different sounds with clearly different meanings that allow these arboreal primates to communicate across tropical forest canopy. The fact that they do not build houses is irrelevant to the gibbons.”

He said domestic pets are also a prime example of the mental abilities of mammals and birds, because of their ability to communicate their demands to us and make us do things for them. "The animal world is much more complex than we give it credit for," he said.

Humans not smarter than animals, just different

Humans have been deceiving themselves for thousands of years that they're smarter than the rest of the animal kingdom, despite growing evidence to the contrary, according to University of Adelaide experts in evolutionary biology.

"For millennia, all kinds of authorities - from religion to eminent scholars - have been repeating the same idea ad nauseam, that humans are exceptional by virtue that they are the smartest in the animal kingdom," says Dr Arthur Saniotis, Visiting Research Fellow with the University's School of Medical Sciences.

"However, science tells us that animals can have cognitive faculties that are superior to human beings."

He says the belief that humans have superior intelligence harks back to the Agricultural Revolution some 10,000 years ago when people began producing cereals and domesticating animals. This gained momentum with the development of organised religion, which viewed human beings as the top species in creation.

"The belief of human cognitive superiority became entrenched in human philosophy and sciences. Even Aristotle, probably the most influential of all thinkers, argued that humans were superior to other animals due to our exclusive ability to reason," Dr Saniotis says.

While animal rights began to rise in prominence during the 19th century, the drive of the Industrial Revolution forestalled any gains made in the awareness of other animals.

Professor Maciej Henneberg, a professor of anthropological and comparative anatomy from the School of Medical Sciences, says animals often possess different abilities that are misunderstood by humans.

"The fact that they may not understand us, while we do not understand them, does not mean our 'intelligences' are at different levels, they are just of different kinds. When a foreigner tries to communicate with us using an imperfect, broken, version of our language, our impression is that they are not very intelligent. But the reality is quite different," Professor Henneberg says.

"Animals offer different kinds of intelligences which have been under-rated due to humans' fixation on language and technology. These include social and kinaesthetic intelligence. Some mammals, like gibbons, can produce a large number of varied sounds - over 20 different sounds with clearly different meanings that allow these arboreal primates to communicate across tropical forest canopy. The fact that they do not build houses is irrelevant to the gibbons.

"Many quadrupeds leave complex olfactory marks in their environment, and some, like koalas, have special pectoral glands for scent marking. Humans, with their limited sense of smell, can't even gauge the complexity of messages contained in olfactory markings, which may be as rich in information as the visual world," he says.

Professor Henneberg says domestic pets also give us close insight into mental abilities of mammals and birds. "They can even communicate to us their demands and make us do things they want. The animal world is much more complex than we give it credit for," he says.

Biology and behavior

There is similar variability in mammals, Dumbacher said. Although all mammal newborns are dependent on their mothers for nutrition, some are more physically capable as newborns than others.

Foals can stand up and walk independently soon after birth because adult female horses are big enough, and can gestate long enough, for their young to develop substantially before birth, making them more physically capable even as newborns, Dumbacher explained.

However, shrews — like songbirds — are born nearly naked and with closed eyes, and must be kept warm by a nest and their mother's body heat.

"With its high metabolic rate and a small body size, it's hard for something like a shrew to carry a baby for a long period of time," Dumbacher said.

Physical and metabolic limitations also apply to human gestation and birth, according to a study published in 2012. [Why Pregnancy Really Lasts 9 Months]

It was already known that the brains — and skulls — of developing babies can't grow bigger than they do in the womb (on average) because they wouldn't fit through the mother's pelvis. The study found that a nine-month gestation period (again, on average) is likely the longest that a woman could safely sustain the accelerated metabolic rate required during pregnancy.

But self-sufficiency of mammal newborns is dependent on more than a species' size and metabolic rate, Dumbacher added. "It's also determined by the ecology of the species, and how much of their behavior can be coded in instinct versus how much has to be learned from their parents," he said.

In other words, the more information about behavior that a juvenile has to absorb from adults of its own kind, the more important the role of long-term parental care is in integrating a young newcomer into the patterns and practices of the group.

That starts to explain the long road that a human baby must travel from helpless newborn, to child, to adult, considering how much they need to learn from their parents about communication and social behavior.

Why some creatures in the deep sea grow to enormous sizes

Deep sea gigantism (or abyssal gigantism) is the tendency for deep-sea animals, mostly invertebrates, to grow to much larger sizes than their shallow water relatives. But what causes animals to grow so much, and what giant animals can we find in the deep sea? Let’s have a look.

Examination of a 9 m (30 ft) giant squid, the second largest cephalopod, that washed ashore in Norway. Image via Wikipedia

When Jacques Piccard and Navy Lieutenant Don Walsh reached dove to a depth of 10,911 metres (35,797 ft) in the Trieste Bathyscaphe, they came in contact with a whole new world. The descent to the ocean floor took 4 hours 47 minutes, and when they finally reached the bottom of Earth’s deepest point, they were shocked to see some species of fish (sole and flounder) casually swimming around. Since then, we’ve learned and discovered much more about deep sea life, but it still feels like we’re only scratching the surface. Biologists still aren’t certain why some abyssal creatures grow to such immense sizes, but they have some good theories.

You’d think that if anything, deep sea pressure would keep animals smaller, and not larger, but the water pressure isn’t much of an issue, because the creatures are mostly water themselves, and water is not very compressible. In fact, the buoyancy of the organism is what allows them to grow so large – they don’t need to fight gravity. But still this explains how they can become so huge, and not why.

Two general rules seem to dictate this growth: Kleiber’s rule and Bergmann’s rule. Kleiber’s rule states that animals that are bigger are generally more efficient. A cat for example, having a mass 100 times that of a mouse, will have a metabolism roughly 32 times greater than that of a mouse. Kleiber’s law, as many other biological allometric laws, is a consequence of the physics and geometry of animal circulatory systems. It also has a lot to do with surface area to volume and the fractal nature of blood vessels. Huge animals swimming in the depths of the oceans rely on food to drop from above, and food is often scarce, so they have every incentive to become more efficient – and therefore larger.

Bergman’s rule is a general correlation of increasing body size with decreasing temperature. Populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions – but this is tendency more than a rule. For warm blooded animals this happens because the bigger you are, the less area you have in contact with the surrounding environment compared to your volume. But for animals swimming in the sea, this is correlated to cell division and increased life span. But there is some debate regarding this rule, and other factors also contribute to the body growth.

Gigantic deep-sea animals

Now that we’ve seen the main (proposed) causes why some animals grow so much deep in the oceans, let’s look at some examples.

Colossal squid (Mesonychoteuthis hamiltoni)

We’ve already seen the giant squid, but there’s also the colossal squid. Believed to be the largest squid species. Researchers believe it can grow up to 14 meters and measure 750 kg. Specimens have been trawled from depths of more than 7,000 feet. Unlike the giant squid, whose arms and tentacles only have suckers lined with small teeth, the colossal squid’s limbs are also equipped with sharp hooks. The colossal squid can hunt and eat sperm whales.

Giant tube worm (Riftia pachyptila)

The giant tube worm. Image via Wikipedia.

In 1977, scientists in the DSV Alvin discovered black smokers (hydrothermal vents that look similar to the video of the Deepwater Horizon gusher) off the Galapagos Islands. Today we know that these hydrothermal vents create entirely new and unique ecosystems – ecosystems in which creatures like the giant tube worm can survive. These worms can reach a length of 2.4 m (7 ft 10 in) and their tubular bodies have a diameter of 4 cm (1.6 in).

Japanese spider crab (Macrocheira kaempferi)

They can grow much more than this. Image via Metro.

You’d think that crabs just hang around in shallow waters, right? Well, you’d be wrong. Adult Japanese spider crabs can be found at depths of over 6,000 meters, and they can reach immense sizes, up to 12 meters from claw to claw. Specimens that weigh almost 20 kgs were found.

Giant isopode (Bathynomus giganteus)

Giant isopodes are abundant in the cold deep waters of the Atlantic, Pacific and Arctic oceans. Giant isopods are a good example of deep-sea gigantism. While generally, isopodes reach between 8 and 15 centimetres, these giant species can reach a maximum weight and length of approximately 1.7 kilograms (3.7 lb) and 76 centimetres (30 in) respectively.

4 More Likely To Fall For The Gambler&rsquos Fallacy

The gambler&rsquos fallacy is a logical fallacy we&rsquore all prone to falling for due to how our brains our designed. While it&rsquos a bit complicated to explain in a single sentence, in essence, it&rsquos the belief that because something has happened a lot in a given period of time, it&rsquos less likely to happen in the future (or vice versa), even if there&rsquos no reason to believe that&rsquos the case. It&rsquos applicable in a lot of cases in real life, the most apparent of them being gambling (hence the name), where gamblers keep expecting a different outcome for the next round based on repetition in previous outcomes.

Surprisingly, smarter people are much more likely to fall for the gambler&rsquos fallacy than others, according to a study conducted on a group of highly intelligent Chinese college students. [7] While we don&rsquot quite understand why that is, it&rsquos possible that intelligent people are also more rigid in their emotional decision-making, which doesn&rsquot allow them to rationally ascertain the likelihood of future events based on past occurrences.

3. Moral Equality Theories

The final theories to discuss are the moral equality theories. On these theories, not only do animals have direct moral status, but they also have the same moral status as human beings. According to theorists of this kind, there can be no legitimate reason to place human beings and animals in different moral categories, and so whatever grounds our duties to human beings will likewise ground duties to animals.

A. Singer and the Principle of Equal Consideration of Interests

Peter Singer has been very influential in the debate concerning animals and ethics. The publication of his Animal Liberation marked the beginning of a growing and increasingly powerful movement in both the United States and Europe.

Singer attacks the views of those who wish to give the interests of animals less weight than the interests of human beings. He argues that if we attempt to extend such unequal consideration to the interests of animals, we will be forced to give unequal consideration to the interests of different human beings. However, doing this goes against the intuitively plausible and commonly accepted claim that all human beings are equal. Singer concludes that we must instead extend a principle of equal consideration of interests to animals as well. Singer describes that principle as follows:

The essence of the Principle of Equal Consideration of Interests is that we give equal weight in our moral deliberations to the like interests of all those affected by our actions (Singer, 1993: 21).

Singer defends this principle with two arguments. The first is a version of the Argument from Marginal Cases the second is the Sophisticated Inegalitarian Argument.

I. The Argument from Marginal Cases (Again)

Singer’s version of the Argument from Marginal Cases is slightly different from the version listed above. It runs as follows:

  1. In order to conclude that all and only human beings deserve a full and equal moral status (and therefore that no animals deserve a full and equal moral status), there must be some property P that all and only human beings have that can ground such a claim.
  2. Any P that only human beings have is a property that (some) human beings lack (e.g., the marginal cases).
  3. Any P that all human beings have is a property that (most) animals have as well.
  4. Therefore, there is no way to defend the claim that all and only human beings deserve a full and equal moral status.

Singer does not defend his first premise, but does not need to the proponents of the view that all and only humans deserve a full and equal moral status rely on it themselves (see the discussion of Direct but Unequal Theories above). In support of the second premise, Singer asks us to consider exactly what properties only humans have that can ground such a strong moral status. Certain properties, such as being human, having human DNA, or walking upright do not seem to be the kind of properties that can ground this kind of status. For example, if we were to encounter alien life forms that did not have human DNA, but lived lives much like our own, we would not be justified in according these beings a weaker moral status simply because they were not human.

However, there are some properties which only human beings have which have seemed to many to be able to ground a full and equal moral status for example, being rational, autonomous, or able to act morally have all been used to justify giving a stronger status to human beings than we do to animals. The problem with such a suggestion is that not all human beings have these properties. So if this is what grounds a full and equal moral status, it follows that not all human beings are equal after all.

If we try to ensure that we choose a property that all human beings do have that will be sufficient to ground a full and equal moral status, we seemed to be pushed towards choosing something such as being sentient, or being capable of experiencing pleasure and pain. Since the marginal cases have this property, they would be granted a full and equal moral status on this suggestion. However, if we choose a property of this kind, animals will likewise have a full and equal moral status since they too are sentient.

The attempt to grant all and only human beings a full and equal moral status does not work according to Singer. We must either conclude that not all human beings are equal, or we must conclude that not only human beings are equal. Singer suggests that the first option is too counter-intuitive to be acceptable so we are forced to conclude that all animals are equal, human or otherwise.

Ii. The Sophisticated Inegalitarian Argument

Another argument Singer employs to refute the claim that all and only human beings deserve a full and equal moral status focuses on the supposed moral relevance of such properties as rationality, autonomy, the ability to act morally, etc. Singer argues that if we were to rely on these sorts of properties as the basis of determining moral status, then we would justify a kind of discrimination against certain human beings that is structurally analogous to such practices as racism and sexism.

For example, the racist believes that all members of his race are more intelligent and rational than all of the members of other races, and thus assigns a greater moral status to the members of his race than he does do the members of other races. However, the racist is wrong in this factual judgment it is not true that all members of any one race are smarter than all members of any other. Notice, however, that the mistake the racist is making is merely a factual mistake. His moral principle that assigns moral status on the basis of intelligence or rationality is not what has led him astray. Rather, it is simply his assessment of how intelligence or rationality is distributed among human beings that is mistaken.

If that were all that is wrong with racism and sexism, then a moral theory according to which we give extra consideration to the very smart and rational would be justified. In other words, we would be justified in becoming, not racists, but sophisticated inegalitarians. However, the sophisticated inegalitarian is just as morally suspect as the racist is. Therefore, it follows that the racist is not morally objectionable merely because of his views on how rationality and intelligence are distributed among human beings rather he is morally objectionable because of the basis he uses to weigh the interests of different individuals. How intelligent, rational, etc., a being is cannot be the basis of his moral status if it were, then the sophisticated inegalitarian would be on secure ground.

Notice that in order for this argument to succeed, it must target properties that admit of degrees. If someone argued that the basis of human equality rested on the possession of a property that did not admit of degrees, it would not follow that some human beings have that property to a stronger degree than others, and the sophisticated inegalitarian would not be justified. However, most of the properties that are used in order to support the claim that all and only human beings deserve a full and equal moral status are properties that do admit of degrees. Such properties as being human or having human DNA do not admit of degrees, but, as already mentioned, these properties do not seem to be capable of supporting such a moral status.

Iii. Practical Implications

In order to implement the Principle of Equal Consideration of Interests in the practical sphere, we must be able to determine the interests of the beings that will be affected by our actions, and we must give similar interests similar weight. Singer concludes that animals can experience pain and suffering by relying on the argument from analogy (see the discussion of Cartesian Theories above). Since animals can experience pain and suffering, they have an interest in avoiding pain.

These facts require the immediate end to many of our practices according to Singer. For example, animals that are raised for food in factory farms live lives that are full of unimaginable pain and suffering (Singer devotes an entire chapter of his book to documenting these facts. He relies mainly on magazines published by the factory farm business for these facts). Although human beings do satisfy their interests by eating meat, Singer argues that the interests the animals have in avoiding this unimaginable pain and suffering is greater than the interests we have in eating food that tastes good. If we are to apply the Principle of Equal Consideration of Interests, we will be forced to cease raising animals in factory farms for food. A failure to do so is nothing other than speciesism, or giving preference to the interests of our own species merely because of they are of our species.

Singer does not unequivocally claim that we must not eat animals if we are to correctly apply the Principle of Equal Consideration of Interests. Whether we are required to refrain from painlessly killing animals will depend on whether animals have an interest in continuing to exist in the future. In order to have this interest, Singer believes that a being must be able to conceive of itself as existing into the future, and this requires a being to be self-conscious. Non-self-conscious beings are not harmed by their deaths, according to Singer, for they do not have an interest in continuing to exist into the future.

Singer argues that we might be able to justify killing these sorts of beings with The Replaceability Argument. On this line of thought, if we kill a non-self-conscious being that was living a good life, then we have lessened the overall amount of good in the world. This can be made up, however, by bringing another being into existence that can experience similar goods. In other words, non-self-conscious beings are replaceable: killing one can be justified if doing so is necessary to bring about the existence of another. Since the animals we rear for food would not exist if we did not eat them, it follows that killing these animals can be justified if the animals we rear for food live good lives. However, in order for this line of argumentation to justify killing animals, the animals must not only be non-self-conscious, but they must also live lives that are worth living, and their deaths must be painless. Singer expresses doubts that all of these conditions could be met, and unequivocally claims that they are not met by such places as factory farms.

Singer also condemns most experimentation in which animals are used. He first points out that many of the experiments performed using animal subjects do not have benefits for human beings that would outweigh the pain caused to the animals. For example, experiments used to test cosmetics or other non-necessary products for human beings cannot be justified if we use the Principle of Equal Consideration of Interests. Singer also condemns experiments that are aimed at preventing or curing human diseases. If we are prepared to use animal subjects for such experiments, then it would actually be better from a scientific point of view to use human subjects instead, for there would be no question of cross-species comparisons when interpreting the data. If we believe the benefits outweigh the harms, then instead of using animals we should instead use orphaned infants that are severely cognitively disabled. If we believe that such a suggestion is morally repugnant when human beings are to be used, but morally innocuous when animals are to be used, then we are guilty of speciesism.

Likewise, hunting for sport, using animals in rodeos, keeping animals confined in zoos wherein they are not able to engage in their natural activities are all condemned by the use of the Principle of the Equal Consideration of Interests.

B. Regan and Animal Rights

Tom Regan’s seminal work, The Case for Animal Rights, is one of the most influential works on the topic of animals and ethics. Regan argues for the claim that animals have rights in just the same way that human beings do. Regan believes it is a mistake to claim that animals have an indirect moral status or an unequal status, and to then infer that animals cannot have any rights. He also thinks it is a mistake to ground an equal moral status on Utilitarian grounds, as Singer attempts to do. According to Regan, we must conclude that animals have the same moral status as human beings furthermore, that moral status is grounded on rights, not on Utilitarian principles.

Regan argues for his case by relying on the concept of inherent value. According to Regan, any being that is a subject-of-a-life is a being that has inherent value. A being that has inherent value is a being towards which we must show respect in order to show respect to such a being, we cannot use it merely as a means to our ends. Instead, each such being must be treated as an end in itself. In other words, a being with inherent value has rights, and these rights act as trumps against the promotion of the overall good.

Regan relies on a version of the Argument from Marginal Cases in arguing for this conclusion. He begins by asking what grounds human rights. He rejects robust views that claim that a being must be capable of representing itself as legitimately pursuing the furtherance of its interests on the grounds that this conception of rights implies that the marginal cases of humanity do not have rights. However, since we think that these beings do have moral rights there must be some other property that grounds these rights. According to Regan, the only property that is common to both normal adult human beings and the marginal cases is the property of being a subject-of-a-life. A being that is a subject-of-a-life will:

have beliefs and desires perception, memory, and a sense of the future, including their own future an emotional life together with feelings of pleasure and pain preference- and welfare-interests the ability to initiate action in pursuit of their desires and goals a psychological identity over time and an individual welfare in the sense that their experiential life fares well or ill for them, logically independently of their utility for others, and logically independently of their being the object of anyone else’s interests (Regan, 1983: 243).

This property is one that all of the human beings that we think deserve rights have however, it is a property that many animals (especially mammals) have as well. So if these marginal cases of humanity deserve rights, then so do these animals.

Although this position may seem quite similar to Singer’s position (see section III, part A above), Regan is careful to point to what he perceives to be the flaws of Singer’s Utilitarian theory. According to Singer, we are required to count every similar interest equally in our deliberation. However, by doing this we are focusing on the wrong thing, Regan claims. What matters is the individual that has the interest, not the interest itself. By focusing on interests themselves, Utilitarianism will license the most horrendous actions. For example, if it were possible to satisfy more interests by performing experiments on human beings, then that is what we should do on Utilitarian grounds. However, Regan believes this is clearly unacceptable: any being with inherent value cannot be used merely as a means.

This does not mean that Regan takes rights to be absolute. When the rights of different individuals conflict, then someone’s rights must be overriden. Regan argues that in these sorts of cases we must try to minimize the rights that are overriden. However, we are not permitted to override someone’s rights just because doing so will make everyone better off in this kind of case we are sacrificing rights for utility, which is never permissible on Regan’s view.

Given these considerations, Regan concludes that we must radically alter the ways in which we treat animals. When we raise animals for food, regardless of how they are treated and how they are killed, we are using them as a means to our ends and not treating them as ends in themselves. Thus, we may not raise animals for food. Likewise, when we experiment on animals in order to advance human science, we are using animals merely as a means to our ends. Similar thoughts apply to the use of animals in rodeos and the hunting of animals.