One day after swimming front crawl, which works the triceps nicely, it all became clear. The triceps muscle has a curious shape at the top on account of its three 'heads' — or connecting origins. And the name derives from tri-ceps from Latin meaning three-heads. And so it goes. The biceps is a two-headed muscle attached with a long and short connection at the top. And the more complicated quadriceps has four heads that attach at the top, though they're a little harder to see.

Beyond this concept finally clicking for me, it was fun to emulate some of the anatomical graphical style of Leonardo Da Vinci — perhaps the ultimate at sketchplanations? — which I have long admired. For inspiration, this is a cracking collection: Leonardo Da Vinci the Graphic Works.

Biceps, triceps, quadriceps

For almost all mammals, 1.5 billion heartbeats, more or less, is how much you’ve got. From the teeniest, tiniest shrew weighing just a few grams to the largest whale — passing through animals as diverse as robins, monkeys, sea lions, and giraffes — each mammal has broadly in the region of 1.5 billion heartbeats.

Beyond just heart rate, knowing a mammal’s weight can help predict several other fundamental aspects of its life. A tiny mammal will likely 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 most significant outlier is us, mainly because, in recent years, we’ve significantly extended our lifetime from what would be expected from Nature.

This gem, and many other fascinating insights about size, scale, Nature and physics, from the book 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 the 1971 book, Discovering Sea Shells by Barry Charles

Typical gastropod anatomy

Phoenix trees are trees that live on after toppling and that can create new trees from branches of the original with their own roots and everything. They are named after the mythical phoenix, a bird that rises from the ashes to regenerate after death, much like Fawkes from Harry Potter.

In phoenix trees I've seen, a large toppled tree hasn't completely separated from its roots—where some roots are broken as the tree fell,  one side of the roots has managed to remain connected. This provides a lifeline for the now horizontal tree.

Remarkably, those branches along the trunk that are now growing upwards can become like trees in their own right and, at times, even put down their own roots. These side trees remain supported by the original great, toppled tree. 

Phoenix trees are 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.

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

What is the difference between venomous and poisonous?

Venomous animals inject venom through bites, stings and the like, though they often avoid it—think snakes, spiders, stingrays, wasps, etc.

Poisoning is when a poison is passively transferred to us through absorbing, consuming or inhaling it—think amphibians, plants, fungi, etc. It might be through touching the skin of a poisonous frog, eating a poisonous animal or breathing in poisonous spores.

Just a few animals manage to be both venomous and poisonous, such as some snakes that inject venom and also have toxic skin from eating poisonous toads.

And a third category you'll know to steer clear of is toxungenous animals that spray, fling or spit toxins toward potential threats. These include the skunk or the aptly named bombardier beetle that sprays acid from its rear.

Fortunately, our instincts are well-trained from centuries of evolution and experience to avoid anything venomous or poisonous, but one day, it may pay to know the difference.

This sketch features in my book Big Ideas Little Pictures

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

How to identify a douglas fir? I find identifying the sometimes subtle differences of tall evergreens rather difficult, but fortunately, that's not the case for the douglas fir.

Identifying a douglas fir, a tall, straight and very impressive evergreen conifer is easy with this simple reminder if you find any cones. Normally, the cones are easy to find around the base of a tree. For such a large tree, like the redwood or sequoia, the cones are quite small.

Douglas fir cones have many small 3-pointed tongues (or bracts) that emerge from the tight cones. Typically, they are of unequal lengths with the longest in the centre. After it came to mind to name each one Dougie, Douglas, and Doug, in turn, after the length of each point, I haven’t forgotten since and identifying a douglas fir is easy.

Mature douglas firs typically have grey, tough and deeply-fissured bark to go with it.

The douglas fir, one of my favourite trees, might even have grown above the tallest redwoods living today making the douglas fir one of the tallest known trees.

The Douglas fir is named after Scottish botanist David Douglas and is not a true fir tree and so it's sometimes written Douglas-fir.

Also see: Ponderosa pine fire protections, nurse log, phoenix trees

Identify a Douglas fir

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?

Biology sketches