To answer this, i’m going to use the Centre for disease control’s answer (CDC in the US) as they are the most reliable source and many theories (some more scientifically sound than others) exist:
The earliest known case of infection with HIV-1 in a human was detected in a blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of the Congo. (How he became infected is not known.) The virus causing AIDS was identified in 1983. The virus was actually called HTLV-III/LAV (human T-cell lymphotropic virus-type III/lymphadenopathy-associated virus).This name was later changed to HIV (probably because it was easier to say!)
For many years scientists theorized as to the origins of HIV and how it appeared in the human population, most believing that HIV originated in other primates. Then in 1999, an international team of researchers reported that they had discovered the origins of HIV-1, the predominant strain of HIV in the developed world. A subspecies of chimpanzees native to west equatorial Africa had been identified as the original source of the virus. The researchers believe that the chimpanzee version of the immunodeficiency virus (called simian immunodeficiency virus or SIV) most likely was transmitted to humans and mutated into HIV when humans hunted these chimpanzees for meat and came into contact with their infected blood. Over decades, the virus slowly spread across Africa and later into other parts of the world.
In order to fully answer your question, we might need to go back to the question “what was the first diseases and how did they emerge?” Therefore we need to understand the evolution and origin of diseases. I don’t want to write a 1000-word essay on it but I want to introduce you to two concepts which might help you to understand disease transmission: the first one is called horizontal gene transfer which is the transfer of genes between organisms in a manner other than traditional reproduction. For instance, if we both had been a bacteria (same species), I would be able to transfer some of my genes to you (randomly) even though we don’t have a father-son relationship. This is so unusual concept for us because the we can only pass our genes to our children. Horizontal gene transfer gives an amazing power to bacteria to continuously upgrade (sometimes downgrade) their genomes. This is one of the reasons how they become multiresistant to antibiotics. The second concept that I want to introduce you is actually very similar to horizontal gene transfer and called “horizontal disease transmission” which is the transmission of an infectious agent, like bacteria or virus between members of the same species that are not in a parent-child relationship.
First of all, there are hypotheses on the origin of HIV but there is no biophysical model supporting any of the hypotheses thus we don’t how on earth the monkeys got the HIV. But I’ll try to use these two concepts in an attempt to answer your question. Remember a virus is an infectious agent which can only replicate and survive in a living organism. All the living beings in the world have different immune systems. Virus knows the more competent the host immune system, the less chance there is for virus to survive (I mean virus cannot think and plan like humans but they know). Therefore virus would keep transmission from one host to another until it finds a vulnerable one. Thereafter, it infects the host and reproduce in it. Again, I don’t how the monkeys got it in the first place but they might have acquired it from another living animal or insect which they might caught and eaten.
To answer this, i’m going to use the Centre for disease control’s answer (CDC in the US) as they are the most reliable source and many theories (some more scientifically sound than others) exist:
The earliest known case of infection with HIV-1 in a human was detected in a blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of the Congo. (How he became infected is not known.) The virus causing AIDS was identified in 1983. The virus was actually called HTLV-III/LAV (human T-cell lymphotropic virus-type III/lymphadenopathy-associated virus).This name was later changed to HIV (probably because it was easier to say!)
For many years scientists theorized as to the origins of HIV and how it appeared in the human population, most believing that HIV originated in other primates. Then in 1999, an international team of researchers reported that they had discovered the origins of HIV-1, the predominant strain of HIV in the developed world. A subspecies of chimpanzees native to west equatorial Africa had been identified as the original source of the virus. The researchers believe that the chimpanzee version of the immunodeficiency virus (called simian immunodeficiency virus or SIV) most likely was transmitted to humans and mutated into HIV when humans hunted these chimpanzees for meat and came into contact with their infected blood. Over decades, the virus slowly spread across Africa and later into other parts of the world.
1
In order to fully answer your question, we might need to go back to the question “what was the first diseases and how did they emerge?” Therefore we need to understand the evolution and origin of diseases. I don’t want to write a 1000-word essay on it but I want to introduce you to two concepts which might help you to understand disease transmission: the first one is called horizontal gene transfer which is the transfer of genes between organisms in a manner other than traditional reproduction. For instance, if we both had been a bacteria (same species), I would be able to transfer some of my genes to you (randomly) even though we don’t have a father-son relationship. This is so unusual concept for us because the we can only pass our genes to our children. Horizontal gene transfer gives an amazing power to bacteria to continuously upgrade (sometimes downgrade) their genomes. This is one of the reasons how they become multiresistant to antibiotics. The second concept that I want to introduce you is actually very similar to horizontal gene transfer and called “horizontal disease transmission” which is the transmission of an infectious agent, like bacteria or virus between members of the same species that are not in a parent-child relationship.
First of all, there are hypotheses on the origin of HIV but there is no biophysical model supporting any of the hypotheses thus we don’t how on earth the monkeys got the HIV. But I’ll try to use these two concepts in an attempt to answer your question. Remember a virus is an infectious agent which can only replicate and survive in a living organism. All the living beings in the world have different immune systems. Virus knows the more competent the host immune system, the less chance there is for virus to survive (I mean virus cannot think and plan like humans but they know). Therefore virus would keep transmission from one host to another until it finds a vulnerable one. Thereafter, it infects the host and reproduce in it. Again, I don’t how the monkeys got it in the first place but they might have acquired it from another living animal or insect which they might caught and eaten.
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