There are those who argue that people cannot know in certain terms if animals experience emotion because they cannot speak. This is an inaccurate argument. Most animals have vocal capacity and just like people, they have it for a reason. Therefore, the argument is not about an animal's incapability to speak. Rather, it is about the inability for most people to understand what an animal is saying to them. This is a rather significant difference, for it speaks to the shortcomings of humans and not animals.
Many people in western civilizations have the tendency to compartmentalize what it means to live. This can cause a person to experience distress when confronted with an experience outside their comfort zone of familiarity. This can be seen when a baby first enters a family and people have to learn what each distinctive cry means. Adults do not remember the language, which leads to varied levels of frustration. What the baby is doing is instinctively communicating a particular emotional need.
There are those who will ask if it is fair to compare humans to animals. Absolutely, humans are genetically a mammal species called Homo sapiens sapiens. Although they are the last remaining survivors of the Homo genus, it does not preclude them from being members of the animal kingdom. Actually, there is an ongoing scientific debate as to whether chimps should be categorized in the Homo genus rather than the Pan. University research has found genetic evidence that humans and chimpanzees diverged from the same lineage at approximately the same time.
Common traits are strongest within same animal classifications. This means that humans would have a more instinctual understanding of a mammal's behavior over that of a reptile. There are many similarities between humans and other mammals when expressing emotions, both verbally and nonverbally. In this instance verbally means communication through sound and nonverbally means conveyance through body language or mannerisms.
There are those that will argue that animals are acting on nothing other than instinct and applying "human emotions" to an animal is nothing more than an attempt to "humanize" it. This rationalization is the product of compartmentalization. Mammals, including humans, have core instinctual emotional responses. Though it is part of survival, it does not mitigate the emotional efficacy.
When a stranger approaches a mammal, the immediate response is one of curious caution and heightened awareness. The root of this response is fear. The mammal has to assess if the stranger is a threat that needs to be feared. Children and young animals will often run away from the unknown until a parent indicates that it is safe. The fear was an instinctual response, yet the emotion was experienced.
Both humans and other mammals will sigh with relief and yawn when fatigued or bored. When a human gets angry they will hit, yell, and whine. Similarly, other mammals will swat, make an aggressive sound, and whine. To show affection humans sit close, eat together, and groom one another. Other mammals exhibit identical intimate mannerisms.
Scientists are unable to quantify the existence of emotions in humans so there is little surprise that there is a lack of scientific data supporting it in other animals. It is a condition more mysterious than the existence of an "afterlife" because emotions are tangible and still manage to elude. The cliché that "animals are people too," is a spin-doctored, perhaps politically correct way of saying, "People are animals too." To understand and embrace that knowledge has the power to change the way humans choose to view the animal kingdom.
For those interested, sign the Stop Animal Abuse Initiative.