Visualizing the Relationship Between Cancer and Lifespan
A Newfound Link Between Cancer and Aging?
A new study in 2022 reveals a thought-provoking relationship between how long animals live and how quickly their genetic codes mutate.
Cancer is a product of time and mutations, and so researchers investigated its onset and impact within 16 unique mammals. A new perspective on DNA mutation broadens our understanding of aging and cancer development—and how we might be able to control it.
Mutations, Aging, and Cancer: A Primer
Cancer is the uncontrolled growth of cells. It is not a pathogen that infects the body, but a normal body process gone wrong.
Cells divide and multiply in our bodies all the time. Sometimes, during DNA replication, tiny mistakes (called mutations) appear randomly within the genetic code. Our bodies have mechanisms to correct these errors, and for much of our youth we remain strong and healthy as a result of these corrective measures.
However, these protections weaken as we age. Developing cancer becomes more likely as mutations slip past our defenses and continue to multiply. The longer we live, the more mutations we carry, and the likelihood of them manifesting into cancer increases.
A Biological Conundrum
Since mutations can occur randomly, biologists expect larger lifeforms (those with more cells) to have greater chances of developing cancer than smaller lifeforms.
Strangely, no association exists.
It is one of biology’s biggest mysteries as to why massive creatures like whales or elephants rarely seem to experience cancer. This is called Peto’s Paradox. Even stranger: some smaller creatures, like the naked mole rat, are completely resistant to cancer.
This phenomenon motivates researchers to look into the genetics of naked mole rats and whales. And while we’ve discovered that special genetic bonuses (like extra tumor-suppressing genes) benefit these creatures, a pattern for cancer rates across all other species is still poorly understood.
Cancer May Be Closely Associated with Lifespan
Researchers at the Wellcome Sanger Institute report the first study to look at how mutation rates compare with animal lifespans.
Mutation rates are simply the speed at which species beget mutations. Mammals with shorter lifespans have average mutation rates that are very fast. A mouse undergoes nearly 800 mutations in each of its four short years on Earth. Mammals with longer lifespans have average mutation rates that are much slower. In humans (average lifespan of roughly 84 years), it comes to fewer than 50 mutations per year.
The study also compares the number of mutations at time of death with other traits, like body mass and lifespan. For example, a giraffe has roughly 40,000 times more cells than a mouse. Or a human lives 90 times longer than a mouse. What surprised researchers was that the number of mutations at time of death differed only by a factor of three.
Such small differentiation suggests there may be a total number of mutations a species can collect before it dies. Since the mammals reached this number at different speeds, finding ways to control the rate of mutations may help stall cancer development, set back aging, and prolong life.
The Future of Cancer Research
The findings in this study ignite new questions for understanding cancer.
Confirming that mutation rate and lifespan are strongly correlated needs comparison to lifeforms beyond mammals, like fishes, birds, and even plants.
It will also be necessary to understand what factors control mutation rates. The answer to this likely lies within the complexities of DNA. Geneticists and oncologists are continuing to investigate genetic curiosities like tumor-suppressing genes and how they might impact mutation rates.
Aging is likely to be a confluence of many issues, like epigenetic changes or telomere shortening, but if mutations are involved then there may be hopes of slowing genetic damage—or even reversing it.
While just a first step, linking mutation rates to lifespan is a reframing of our understanding of cancer development, and it may open doors to new strategies and therapies for treating cancer or taming the number of health-related concerns that come with aging.
Visualizing the Biomass of All the World’s Mammals
When the world’s biomass—the stuff we’re made of—is tallied up, humans and cattle outweigh wild mammals by a massive margin.
Visualizing the Biomass of All the World’s Mammals
Even as we understand more about the world we live in, certain aspects of it remain undefined or hard to comprehend.
One such example is in the scale and distribution of Earth’s life. What’s the ratio of wild to domesticated animals? How much do all of the world’s humans weigh?
Until recently, such questions were nearly unanswerable. A new report titled The Global Biomass of Wild Mammals helps shed more light on the composition and scale of life on our planet. The research provides an estimate of the biomass of all mammals, globally—including humans.
So, What is Biomass Anyway?
Biomass is simply the weight of living things.
In this study, researchers
created rough estimates for four major categories of mammals: humans, domesticated animals, and those that were found in wild terrestrial and marine environments. A further breakdown of mammal groups are found within each category.
To achieve this, they took the estimated number of species from census data and multiplied it with each species’ average body mass.
One component worth pointing out is that animals contribute very different amounts to the world’s biomass total. For example, whales significantly outweigh rodents in terms of biomass, even though there are fewer species and populations of whales. The fact that whales are so much larger than rodents means that even smaller populations can contribute a meaningful portion to overall biomass.
Mammalian Biomass, Organized Neatly
Each larger cube above represents 20 million metric tons of carbon, and the entirety of the visualization represents all living mammalian life on Earth.
The paper separates mammals into four distinct categories:
|Category||Total Mass (Mt)||Top Sub-Category|
|Domesticated Mammals||651||Cattle (416 Mt)|
|Wild Marine Mammals||40||Baleen Whales (23 Mt)|
|Wild Terrestrial Mammals||24||Even-Hoofed Mammals (11 Mt)|
One of the most obvious takeaways from this data is that humans make up one-third of total mammalian biomass.
Perhaps even more strikingly, the animals we’ve domesticated for food, companionship, and labor make up close to 60% of the total weight of Earth’s mammals. Domesticated dogs and cats alone equal the total weight of all other wild land mammals combined.
The world’s sheep, on their own, weigh as much as all the whales and seals in the ocean. Domesticated buffalo such as the water buffalo, a species commonly found in Asia, combine to have the third largest biomass of all mammals.
Finally, there’s one category of mammal that comes way out on top.
The global livestock population has risen along with the human population, and cattle are now the top mammal in the world by weight.
In fact, just the United States’ share of cattle matches the biomass of all wild mammals on Earth.
As the standard of living continues to rise for people around the world, beef consumption has been increasing in many developing countries. Of course, raising cattle is a resource and land intensive operation, and there have been very real impacts on a global scale. For one, cows are a major source of methane emissions. As well, in Brazil, which accounts for around 25% of the world’s cattle population, pasture has directly replaced large swaths of rainforest habitat.
At the very bottom of the visualization, dwarfed by humans and domesticated mammals, lies the vast array of wild mammals that live on planet Earth.
It’s sobering to see that the biomass of North America’s human population alone compares closely with that of all terrestrial wild mammals in the world. This includes plentiful creatures like rats and mice, as well as large mammals like elephants and bears.
Below are the top 10 wild mammalian contributors to biomass in the natural world.
|Rank||Contributor||Total Mass (Mt)||Individuals (millions)|
|#4T||Antarctic Minke Whales||3||0.5|
In the ocean, whales and seals are the heavyweight champions. On land, deer, and boar come out on top as they are both heavy and plentiful.
Humans have a complicated relationship with large mammals. We feel a very clear connection to these creatures, and they are often the key figures in conservation efforts. That said, even small populations of humans have wiped out large mammal species in the past.
The news that cattle outweigh wild land animals by a factor of 20:1 is a reminder that human influence is perhaps even more powerful than we think.
The more we’re exposed to nature’s full splendor […] the more we might be tempted to imagine that nature is an endless and inexhaustible resource. In reality, the weight of all remaining wild land mammals is less than 10% of humanity’s combined weight. – Ron Milo, Professor of Systems Biology
Source: The global biomass of wild mammals
Data notes: To come up with the numbers above, scientists estimated the total biomass of wild mammals on Earth by manually collecting population estimates for 392 land mammal species, which make up about 6% of all wild land mammal species, and using machine learning to infer the global populations of the remaining 94%. Their estimate includes 4,805 wild land mammal species out of approximately 6,400 known and extant wild land mammal species, excluding low-abundance species for which data are scarce.
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