One of the subjects of the human controversy of our times is whether homosexuality is an acceptable form of human behaviour.
One of the arguments in favour of homosexuality is that homosexuality is "natural, because animals do it". The issue of human "animality" is also relevant to other forms of human behaviour like politics and use of alcohol and drugs.
There are two meanings of the word "natural" relevant to this context:
(1) "existing in nature" and (2) "intended by nature".
Yes, animals can perform what humans can describe as homosexual acts1 and homosexuality is "natural" in sense (1), but the purpose of the sexual organs of animals and humans, and of the distinction between the two sexes is the reproduction of the species, and homosexuality is not "natural" in sense (2).
The second issue is: "Is it right for the humans to do something, because animals do it?".
Animals kill, steal and rape. And all men are born bed-wetters, thieves, rapists and murderers, as well as potentially homosexuals, alcoholics, drug addicts, etc.
The reason that not all people steal, rape, kill or engage in whatever form of sex they might feel an urge to, is because of "education" (in a very general sense of that word).
From the early childhood onward people are taught by their parents, other people, trial and error, logical reasoning, fear of punishment by the state, etc. not to wet their beds, not to steel, not to kill, and to control their sexual urges. This is the difference between humans and animals. This is what "civilization" means.
Some people accept the "constraints" imposed by the civilization, either because they are brought up that way, or because they understand that this is beneficial for Mankind. Others find these "restrictions" uncomfortable and seek to evade them or overcome them. This usually involves seeking a "moral" justification for their behaviour. The attempts to justify homosexuality by saying that it is "natural, because animals do it" is an example of that.
Other examples are the various socialist theories which seek to overcome the restraints of property ownership. And "anarchists" are against any form of constraints on their own behaviour at all. They are only too willing, however, to restrain and interfere with the behaviour of others.
Politics is another example of overcoming civilizational constraints. A politician seeks to place himself into a position of power so that he can put himself above the constraints of law and morality. He becomes "free" to interfere with the life, freedom and property of others. Once in power he feels free to impose on others laws and morality of his own liking, but he himself is governed only by his "political instincts" and is to be judged only by "history".
People for whom the civilizational constraints are an unnatural imposition which they accept only through fear feel constant inward strain and stress from which they want to break free. And the most common way of breaking out of the civilizational constraints is alcohol and other intoxicating substances.
In the initial stages of intoxication, alcohol "liberates" the drinker from the control of his reason and "sets free" his animal instincts. It also frees the drinker from a realistic perception of reality and of himself. And this gives the drinker an illusion of "freedom and power". And this is what they call the "happiness" of being drunk.
By contrast a person who accepts the civilizational constraints not through fear, but through understanding, does not see these constraints as an imposition and a burden, but as a useful navigational instrument which shows him the right direction. For such people their own reason is not a burden from which they want to get rid of by getting drunk or drugged.
Homosexuality, theft, politics are behaviour, not physiological characteristics. There is no special "race" of "homosexuals", who are "born that way", as there is no special race of thieves, murderers, adulterers, etc.. All people are capable of stealing and killing and having uncontrolled sex, but people can control their behavior and are responsible for the results of their actions.
In a healthy civilization the laws and morals of the society ensure that the behaviour of people is not harmful to themselves and others, but is beneficial to themselves and the society as a whole. This is done by encouragement of virtues and discouragement of vices.
Civilizations where vices are encouraged and virtues are discouraged decay and disappear from the face of the Earth.
1) It is wrong, however, to assume that what appears as "homosexuality" in animals is the same as "homosexuality" in humans. For example, animals use tongues to clean their bodies, bodies of their children and even of other animals. So, licking by animals of their private parts is not the same as such acts performed by humans. It could be equivalent to humans washing their private parts, rather than "having oral sex".