Where did disease come from and how did they become their own diseases
In: Biology
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Approximately 12,000 years ago. When we domesticated animals we also invited a multitude of disease. Couple this with close proximity living in built up areas, this contributed to mutations and the like.
Diseases have been around most likely since life has been around. There are two broad categories of disease: (1) Those caused by external entities, and (2) those caused be internal dysfunctions.
The first category includes things like infections, which can be caused by viruses, bacteria, fungi, protists (single celled eukaryotes like the organism that causes malaria), and even other animals (like parasitic worms). The story of how each infectious species evolved to become infectious is different, but broadly speaking, these populations were naturally selected for lifestyles that involved gaining nutrients or reproductive capabilities from other organisms. The disease is caused because the siphoning of nutrients, or the mechanisms of reproduction, end up causing harm to the host, sometimes, to the point of their death.
The second category include things like genetic diseases (inheriting a faulty copy [or copies] of a gene) and cancers (where the mechanisms that constrain cellular reproduction break due to the buildup of mutations in DNA over time). Biology is never perfect. There are always mistakes, and as you live and your cells divide, they don’t always copy your genome perfectly. If these mutations occur in sperm or egg cells, they can be passed onto future generations. If they happen in other cells of the body, in certain types of genes, they can lead to cancers.
We see both categories of diseases in nearly every species that we’ve studied, so there’s no good reason to think disease hasn’t been a problem for all organisms since basically the very first ones.
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