Cancer is fundamentally a disease of uncontrolled cellular growth, where a cell disregards the body’s signals and divides relentlessly. Because this process is rooted in the basic mechanisms of cell division and DNA repair, it is not exclusive to humans or domesticated animals. The simple answer to whether wild animals get cancer is a definitive yes. This phenomenon is a universal consequence of multicellular life, occurring across the animal kingdom wherever cells are rapidly dividing and accumulating genetic damage.
Universal Occurrence: Documented Cases in Diverse Species
The presence of cancer has been documented in nearly every large taxonomic group, confirming it as an ancient biological challenge for multicellular organisms. Cases have been recorded in mammals, birds, reptiles, fish, and even molluscs, underscoring its broad reach across evolutionary history. For instance, a high prevalence of tumors has been observed in specific wild populations, such as California sea lions, where approximately 20% of adult stranded animals that die have cancer. In contrast, some species, like the common porpoise and the black-footed penguin, show remarkably low cancer rates, with fewer than 2% of individuals affected.
Obtaining accurate statistics on cancer in the wild is extremely difficult, meaning documented cases are likely only a small fraction of the true incidence. Wild animals instinctively hide signs of illness to avoid predation, and their typically short lifespans often prevent tumors from growing large enough to be easily noticeable. Most discoveries happen during postmortem examinations or necropsies, which are rare for animals that die in remote locations. This lack of monitoring and the rapid decomposition of remains make the true scope of cancer hard to measure.
Solving the Size Problem: The Mechanisms of Cancer Suppression
The size and longevity of an animal present a biological puzzle known as Peto’s Paradox. Since cancer arises from random mutations, an animal with more cells and a longer lifespan, such as a blue whale, should theoretically have a higher cancer risk than a small, short-lived mouse. However, studies show that cancer risk does not increase linearly with either body size or lifespan across different species. Large, long-lived species must have evolved mechanisms to suppress tumor formation.
African elephants represent an example of this evolutionary adaptation, with a cancer mortality rate of less than 5%. Humans possess one copy of the \(TP53\) tumor suppressor gene, which helps repair DNA and trigger cell death. Elephants, however, possess 20 copies of the \(TP53\) gene, increasing their cellular defense. This genetic redundancy ensures that if DNA damage occurs, the elephant cell is quicker to initiate apoptosis (programmed cell death), eliminating the potentially cancerous cell before it can proliferate.
Other species have developed strategies to achieve cancer resistance. Bowhead whales, which can live for over 200 years, show alterations in genes associated with DNA repair and cell-cycle regulation. Naked mole rats, small rodents with exceptional longevity, employ a mechanism where their cells exhibit an unusual sensitivity to overcrowding. This heightened cellular contact inhibition effectively halts cell division before a tumor can begin to form, showcasing diverse solutions to the same fundamental biological problem.
Cancer as an Infectious Disease: Transmissible Tumors
A rare manifestation of cancer in the wild is its ability to spread like a contagious pathogen. Transmissible cancers occur when living cancer cells physically transfer from one individual host to another, establishing a new tumor. This is distinct from cancer caused by viruses, as the transferred cells are the cancer itself, not a viral agent. Such diseases threaten wildlife populations because they bypass the need for a tumor to arise spontaneously within each individual.
The most well-known example is Devil Facial Tumor Disease (DFTD), which has devastated Tasmanian devil populations since its discovery in 1996. The cancer cells are transferred during the aggressive biting that occurs during feeding and mating rituals. This disease is nearly 100% fatal and has caused population declines of up to 90% in some areas, pushing the species toward extinction.
Another instance is Canine Transmissible Venereal Tumor (CTVT), an ancient cancer that arose thousands of years ago and is transmitted primarily through sexual contact in dogs. Unlike DFTD, CTVT tumors often enter a regressive phase, allowing the host’s immune system to reject the foreign cancer cells, meaning it is rarely fatal. The existence of these transmissible cancers highlights that in the wild, cancer can evolve into a parasitic life form capable of horizontal transmission between hosts.