If you were to guess, what do you think ancient humans used as contraceptives? It's definitely hard to list even a couple of ideas given how far we've come since the start of the 20th century. 

According to historians, the first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Dried dung was inserted into the vagina to form an impenetrable barrier. Other pessaries used back in the day included tree sap, lemon halves, cotton, wool, sea sponges, and elephant dung.

Later on, however, condoms made of animal bladders or intestines were also reportedly used. Luckily, in 1844, Charles Goodyear obtained the first patent for a rubber condom. ...

Some mammals, such as camels, polar bears, and seals, have full nictitating membranes. That is the transparent or translucent third eyelid that can be drawn across the eye for protection and to moisten it while maintaining visibility.

In humans, the plica semilunaris (also known as the semilunar fold) and its associated muscles are thought to be homologous to the nictitating membranes seen in other animals. In most primate species, a plica semilunaris is present, but a fully developed nictitating membranes still exists in lemurs and lorisiform primates.

Unlike the upper and lower eyelids, the nictitating membrane moves horizontally across the eyeball (shown below). In some diving animals, such as beavers and manatees, it moves across the e ...

Regardless of your size, men and women, big or small, all pee at the same average rate — between 1/3 and ½ ounces per second (10 ml to 15 ml per second). Since the mean urine quantity ranges between 1 to 2 quarts a day (1.4 L, on average), we are condemned to spend one to two full minutes peeing daily.

The average lifespan in the United States today is 27,375 days. If we multiplying 27,375 days by 2 minutes per day peeing, that's 54,750 minutes, or 912.5 hours of your lifetime urinating. That also translates into roughly 38 days of your lifetime ...

Summer is officially over, and fall has arrived. With this season comes runny noses and doctor visits. Save yourself the time and money, because it's either the common cold or the flu, both of which have no cure other than to rest and endure the discomfort. Luckily, you can be immunized for the flu, but not the cold. In fact, many people battle the cold several times a year, rather than developing a natural immunity towards it, why is that? 

The primary reason that immunity generally does not develop against the common cold is that there is not a single cause of the disease. Over 200 serotypes of viruses, including enteroviruses (previously called rhinoviruses), coronaviruses, and adenoviruses, can cause the symptoms of the common cold. Ther ...

Birthmarks are congenital marks on the skin that appear at birth and occasionally disappears spontaneously. The term nevus refers to a benign cutaneous tumor consisting of blood capillaries. Such tumors, which rarely spread from their original site and are not dangerous, vary in color according to whether the capillaries composing them carry arterial or venous blood. The popularly termed cherry marks and port-wine stains (shown below) are nevi on a level with the surface of the skin. Certain other vascular nevi, commonly known as strawberry or raspberry marks (scientifically known as hemangiomas), are slightly elevated above the surface. These can appear anywhere on the body's surface, including the airway within the nose. The former Soviet ...

Rodents are mammals characterized by a pair of broad, sharp-edged, chisel-like incisor teeth that are firmly inserted in both jaws and are used in gnawing vegetation. The front surface of each incisor tooth is composed of enamel, and the hind surface is of soft dentine wears away during the process of gnawing so that the teeth are constantly kept sharp. Shown above is a beaver sporting bright orange teeth; the reason they are orange is because of an unusually high concentration of iron in the enamel.

Unlike human teeth, the incisors of rodents don't have roots, and they never stop growing! To keep these teeth from growing into their brains, rodents grind their teeth against each other. This friction is similar to using a grindstone to sharp ...

Did you know that the Moon's rotation is locked to its orbit around Earth by a bulge of material under the Moon's surface? This material is denser than the rest of the Moon's surface material, and Earth's gravity pulls on it especially strongly. The side of the Moon containing the bulge always faces Earth. We call it the near side and we call the other side, which we never see from Earth, the far side. People often mistakenly use the term "dark side" when referring to the far side of the Moon, forgetting that the far side is fully illuminated by the Sun whenever we see a new moon from Earth.

If we were to look from high above the Earth-Moon system, we would see the Moon rotate once per month with respect to the stars. This is its sidereal ro ...

Human smell has often been characterized as being deficient when compared to the smell abilities of some lower organisms. Summarized below are four myths about human smell that have been contradicted by research.

Myth 1: Human smell is less sensitive than that of other animals.

Research indicates that the individual smell receptor cells in humans will respond to a single odorant molecule. The difference in overall sensitivity appears to be due to the fact that some lower organisms, such as dogs, have more smell receptors.

Myth 2: Humans have a relatively poor ability to detect changes in smell intensity.

Although earlier research indicated that the difference threshold for smell was the largest of all the senses, more recent research, carefully ...