If animals were iPads, we would spend our days raving about the brilliance of their design. Take any creature, from a sabre-toothed tiger to a tiny ant, and you'll find it crammed with unique, specialised features that enable its survival on the planet. Or take a fresh look at your reflection in the bathroom mirror - your own skin and hair are a wonder of evolution too.
The skin of a frog is smooth and bare, which prevents it from becoming too hot or cold. They have lungs and take in air through their nostrils and mouth, but absorb additional oxygen through the pores in their skin. Most frogs are a dull brown, grey or green, which is great camouflage as they look like moss or lichen. The tree frog changes from light green to dark brown as the need arises, while there's a small African frog that's creamy white as it lives in lily blossom.
Fishes' scales act like a suit of armour. They are hard and slippery, which makes it difficult for predators to nab them, and they help protect against sharp coral. All fish have scales, even sharks.
All animals shed their skin, but it's not obvious with mammals and humans, as the discarding of dead cells is a continuous process. Reptiles are different because they shed their skin periodically. Snakes' skin comes off in one piece, like a sock, taking parasites with it and allowing the creature to grow. They tend not to eat in the days leading up to shedding as they are vulnerable. Bless 'em.
These lizards are well-known for their colour-changing skin, used as a form of communication with rivals and potential mates. They tend to go darker when angered and courting males show lighter, multicoloured patterns, rather like a chap on a first date selecting his best Paul Smith shirt. When these versatile reptiles aren't engaging in their own form of social media, they revert to a default colour to match their surroundings, such as green for jungle, beige for desert.
This chap shows how fascinated he is with the reptile by stalking this rather rare chameleon.
Mammals' fur keeps their body temperature in check and helps with camouflage, but the porcupine goes the extra mile with self-defence. Its spiky, prickly quills are made of keratin. They may have as many as 30,000 on their backs and tails, which stand up when the porcupine senses danger. Predators generally back off as being stabbed with a quill is bad news.
Bats are the only mammals capable of true flight (as opposed to gliding). Their wing is a stretchy, thin skin called a patagium, which stretches between each finger bone and connects to the ankle and tail. Bats have a single claw that sticks out of the top, which they use to climb, crawl and clean their ears.
Skin is our largest organ, with a surface area of around two square metres. Its thickness varies from 0.5mm on the eyelids to 4mm or more on the palms of the hand and soles of the feet.
We have two main layers, the outer epidermis and inner dermis, which give us sensation and form a tough physical barrier to protect us from sunlight, damage, infection and drying out. Cells on the surface flake off steadily and are continually replaced. We produce a completely new epidermis every 30 days.
Our skin has a number of features:
- Follicles - pore-like structures that produce hair
- Dermal papilla - the origin of all cell growth and division
- Sebaceous glands - secrete oil to protect us from bacteria, provide lubrication and waterproofing. On the scalp, these make our hair soft, shiny and pliable.
- Sudoriferous (sweat) glands - excrete waste in the form of sweat, which evaporates to cool the body.
- Arrector pili muscles - attached to the hair follicles, these contract when we get cold. This pulls the hair upright, giving us goose pimples and trapping warm air around our body to help keep us warm.
Eyebrows provide moderate protection from dirt, sweat and water. They also play a key role by displaying emotions such as sadness, anger, surprise and excitement. In other mammals, they contain much longer, whisker-like hairs that act as tactile sensors.
Eyelashes are to humans (plus camels, horses and ostriches) what whiskers are to cats. They sense when potentially harmful bugs, dirt or dust particles come too close to the eye.
Armpit and groin hair means we can move about without chafing. The hair in and around the ear wards off insects who might find the ear canal a little too interesting.