For almost all mammals that’s more or less how much you got. Remarkably, from the teeniest, tiniest shrew weighing just a few grams, to the largest whale — passing through animals as different as robins, monkeys, sea lions, and giraffes in between — each mammal has broadly in the region of 1.5 billion heartbeats. You can see the striking regularity in the logarithmic chart in the sketch.

What’s more, other aspects of mammals can be predicted to a surprising accuracy simply from their weight. A tiny animal will have a heart that goes like crazy, live only briefly, and reach maturity quickly. A large animal, in contrast, will have a slow heart rate, a long life, and take its time to adulthood.

The biggest outlier is us, largely because in recent years we’ve managed to significantly extend our lifetime from what would be expected from Nature.

This gem I learned once again from Scale by Geoffrey West.

1.5 billion heartbeats in a lifetime

For years, I’ve wondered at how as a kid I found the monkey bars in a playground (often a jungle gym in the US) so much easier to swing on than I do as an adult. And I see our kids swinging around easily on them, while now it’s hard for me just to hang off them. The reason why is partly to do with the square-cube law.

The square-cube law is the deceptively simple observation that as you scale up dimensions — say, as you get taller — then area of the object increases proportional to the square of the length, while volume increases proportional to the cube of length. This fundamental relationship has enormous significance in the sizes and shapes of animals and the limits of how big trees can get and how big we can build our bridges and buildings.

Because the strength of our bones, muscles or wooden beams is proportional to their cross-sectional area, this means that while the strength of a larger object, assuming the same proportions as the smaller one, increases according to the square of a length, the weight (from the volume it takes up) increases according to the cube of a length. So, relative strength decreases as size increases.

Some corollaries are therefore that children’s small size relative to the area of their muscles and bones makes them relatively stronger than adults and so they can more easily support their weight as they swing on the monkey bars. In the same way, press ups are harder for bigger people than they are for smaller. And while an ant has tiny spindly legs, those legs could easily support 50 other ants of its size, whereas for an elephant to support its own weight it needs chunky legs — not spindly ones — and there’s no chance it could get close to carrying 50 other elephants on its back.

It’s also part of the reason short trees can be spindly, but big sequoias have relatively chunkier trunks, and we need increasingly strong materials to build bigger and bigger skyscrapers compared to the shed in your garden.

Galileo discussed this back in 1638 and it still requires some getting your head around today.

For this and other fascinating insights of scaling check out Scale, by Geoffrey West.

The Square-Cube law

The name for the troubling observation that where windscreens used to be covered in squashed bugs after a long drive, these days you’ll tend to see your windscreen remains squashed-bug free.

It’s believed this reflects a real and significant decline in insect numbers. Though tracking insect numbers is, however, rather tricky as you could imagine. So don’t ignore bugs, or treat them as pests, value them and, if you have a garden, try to provide some habitat to help them out. Here’s a good article about the windscreen phenomenon.

The Windscreen Phenomenon

These days beards are in. There will come a day when beards are out. And a day when beards are back in again. That’s how it seems to go.

Turns out there is a name for this kind of thing: negative frequency-dependent selection. Essentially, the less common it is, the more useful a trait it is. As opposed to positive frequency-dependent selection which, as you can imagine, is the reverse.

According to this study, for example, when there are fewer men with beards in a population, they are judged as more attractive than when there are more of them. Hence they become gradually more popular until the effect starts to wear off and the clean-shaven look starts to appeal again. And round the cycle we go.

The beard cycle

Not the easiest switch to make but given that jellyfish and starfish are not at all fish there is a move to call them sea jelly and sea star. As long as we all work to help protect them clearly it doesn’t matter a whole lot, but I think the move to sea jellies and sea stars makes good sense alongside others like the sea horse, sea cucumber, sea lion, sea lily, sea gooseberry…well, actually the sea horse is a type of fish, but you get the idea.

Sea jelly, sea star

For a closer look next time you’re at the beach. Pay close attention to whether you find one with a dextral or sinistral aperture.

Gastropods are the largest class of molluscs which includes limpets, snails and sea slugs. For those who weren’t sure.

Info from Discovering Sea Shells by Barry Charles

Typical gastropod anatomy

Trees that live on after toppling and that can create new trees from branches of the original with their own roots and everything. Not to be confused with nurse logs which are dead fallen trees that provide a great environment for new trees and plants to grow in. When the original finally decays you end up with a neat straight line of trees.

Phoenix trees

Our ability to sense position and movement of joints and limbs. It’s how you can tell where your right foot is now even without looking. Alcohol screws with it and touching your nose with your eyes closed if often used as part of sobriety tests. Maybe try it yourself next time you’re drunk?

Proprioception

Venomous animals inject venom through bites, stings and the like. Think snakes, spiders, stingrays…

Poisonous animals poison you if you absorb - perhaps by touching the skin of a poisonous frog - consume - perhaps by eating a poisonous animal - or inhale the poison - perhaps by breathing in some poisonous spores. Think amphibians, plants, fungi…

Venomous, poisonous - what’s the difference

All of these guys can grow back major parts of their body, even limbs, and in the case of the flatworm a new head. Crazy.

Animals that regenerate

Homo sapiens. Our place in the order of things

A centipede has 1 pair of legs on each body ring, and a millipede has two on most body segments. Hence millipedes will generally have plenty more legs to go round. As far as I know this is fairly foolproof. Though generally speaking there are more obvious ways to tell, such as millipedes looking more like long armoured nice round worms and usually moving slowly, and centipedes zipping around while generally seeming more long-legged and insecty, with longer antennae at the front and longer angled back legs, sometimes with hooks for defence.

If you were offered to pick one of them up, you’d probably pick the millipede.

Also, in case you were tempted to think they are insects, they’re not because insects have six legs. They are arthropods (loosely meaning jointed feet) along with insects, spiders, scorpions and crustaceans, but in their own subphylum of, aptly named, myriapoda (loosely meaning many legs).

Check out core insect anatomy for a sketchplanation insect refresher.

How to tell a centipede from a millipede

Nifty water camouflage practised by dolphins, porpoises, some fish and other neat sea creatures. The simple strategy: look light like the sky for anyone below, and look dark like the sea for anyone above. 

Counter-shading

Turns out a bunch of substances have the power to make you sleepy - tryptophan, vitamin B6, calcium, glycine, lactucarium and carbohydrates are some of the major ones. Some even interact with each other for maximum sleepiness. A few common foods with these compounds in good measure include:

turkey, walnuts - tryptophan
tuna, pistachios - vitamin B6
dairy - calcium
chamomile - glycine
lettuce - lactucarium

So an evening turkey or tuna, walnut, cheese and lettuce sandwich with a glass of milk and a side of pistachios or walnuts and you’ll be set for a good night.

Sleepy foods

Pay attention to the jaw, teeth, habitat and location and you’ll be 99%.

What’s the difference between a crocodile and an alligator

Reproduction. Excess. Variation. Selection. Divergence.

Darwin’s 5 principles of Natural Selection

And straighter hair is rounder. You can demonstrate this with a strand of you hair by gripping it between the nails of two fingers and squeezing all the way down. As you make it oval, you’ll also see it curl.

Apologies to those who caught this earlier. I accidentally posted several in a row and removed them to post one at a time. Really sorry if it disappeared from your blog, and thanks for sharing.

Curly hair is oval

Head, thorax - with 6 legs or wings, abdomen and an exoskeleton and you have an insect. One of over a million species. As impressive as snowflakes.

Core insect anatomy

After getting pretty serious RSI many years back I was forced to start doing more things with my ‘other’ hand. It takes time and practice, but hey, you can already do these things with one hand - why not learn a little more during everyday life?

Sketchplanations tagged with biology