The BBC Attempts to Answer the Impossible Question

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Story at-a-glance -

  • A listener of the BBC's More or Less program asked how many animals are born every day
  • Numbers vary dramatically by species; it’s estimated that more than 1.9 million rabbits are born daily in the U.K. in contrast to more than 62 million chickens, born worldwide every day
  • Only 40 Humboldt penguin chicks are born daily worldwide compared to an estimated 371 million honey bees in the U.K.
  • The most striking example of all, however, came from one of the “lowliest” lifeforms: the roundworm (or nematode), which congregates to the tune of 3 million per square meter of land; 600 quintillion nematodes are born on Earth every day

By Dr. Karen Shaw Becker

Have you ever wondered how many animals are born every day? It seems like a rhetorical question, but one listener of the BBC's More or Less program, which attempts to answer such striking numbers-based questions as this one, asked just that — and expected an answer.1 To estimate this number in its entirety is likely impossible, not only because little is known about many species reproductive habits but also because much of the Earth, particularly the oceans, has yet to be explored.

Still, the program did make an attempt, starting with defining the term “animal,” which they took from the Oxford English Dictionary to include mammals and non-mammals, vertebrates and invertebrates. They then started to answer this seemingly unanswerable question by breaking it down to a few key species.

How Many Animals Are Born Every Day?

No discussion of animal reproduction would be complete without discussing rabbits, which have earned quite the reputation as prolific breeders. So that’s where the BBC started. There are an estimated 40 million breeding rabbits in the U.K., which produce an average of seven litters each with five kittens per litter. This equates to more than 1.9 million rabbits born daily — and that’s just in the U.K.

They then moved on to Humboldt penguins, a threatened species, which live in Chile and Peru. Humboldt penguins lay only two eggs at a time, typically twice a year, and it’s estimated that 14,400 hatch in the wild every year. This amounts to about 40 Humboldt chicks born daily. As for another type of chicks — chickens — the BBC used data from the Food and Agriculture Organization of the United Nations to estimate that more than 62 million are born worldwide every day.

As for honey bees, based on the fact that a queen honey bee may lay 1,500 eggs a day, and the count of nearly 250,000 honeybee hives in the UK, they estimated more than 371 million honey bees could hatch in the U.K. daily. The most striking example of all, however, came from one of the “lowliest” lifeforms: the roundworm (or nematode), which congregates to the tune of 3 million per square meter of land.

Caenorhabditis Elegans, or C. Elegans, is just one species of nematode, which is known to lay five eggs per hour with, according to professor Axel Rossberg, Ph.D., from Queen Mary's University, a 1 percent hatch rate. According to the BBC:

“When multiplied by the number of square meters of land on earth — which is around about 150,000,000,000,000 — this comes out at 600 quintillion nematodes born per day on land on earth every single day. When the rest of the global nematode population, which lives in water, is taken into account, this figure is much, much, higher.”

So to answer the question of how many animals are born daily worldwide, the answer is simple: a lot!

How Many Different Species Exist on Earth?

Another interesting question worth tackling is how many species exist on Earth. A collaboration of species turned to taxonomy developed in the 1700s to make an educated guess. Species that are related are grouped in the same genus, then according to families, which are further broken down into orders, classes, phyla and kingdoms. It’s rare for a new class or order to be discovered (as well as anything higher up in this tree of life), while new species discoveries further down are still occurring regularly.2

“The higher taxonomic classification of species (i.e., the assignment of species to phylum, class, order, family, and genus) follows a consistent and predictable pattern from which the total number of species in a taxonomic group can be estimated,” the researchers wrote in PLOS Biology, which they estimated to be about 8.7 million Earthly species.3

This includes mostly animals (7.77 million), followed by fungi (0.61 million), plants (0.30 million), protozoa (0.04 million) and chromists, such as algae (0.03 million). Of them, only about 1.2 million have been described whereas “86 [percent] of existing species on Earth and 91 [percent] of species in the ocean still await description,” they noted, adding:

“The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science. Yet the answer to this question remains enigmatic, as efforts to sample the world's biodiversity to date have been limited and thus have precluded direct quantification of global species richness, and because indirect estimates rely on assumptions that have proven highly controversial.”

At this rate, not only would it take more than 1,000 years to catalogue all 8.7 million species on the planet, but many could become extinct before researchers have a chance to do so. More than 8 million species sounds like a lot, until you consider another study that included bacterial species in the mix.

The researchers used scaling laws developed for plants and animals for microorganisms, revealing that when microorganisms such as bacteria are included, there are upwards of 1 trillion species on Earth — and only one-thousandth of 1 percent have been identified.4 “Microbial biodiversity seems greater than ever anticipated yet predictable from the smallest to the largest microbiome,” the researchers noted.5 I’m not sure which is more fascinating: the sheer number of species on Earth or the fact that so many remain unexplored!

This is just one reason why conservation efforts are so important: if we don’t take steps to protect biodiverse regions in the world — like rainforests, which likely contain one-half to three-quarters of the different species on the planet,6 and oceans — we could be witnessing the extinction of species before we’re even aware that they exist.