|
|
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
The modern decimal position system was the invention of the Hindus (around 800 AD), involving the placing of numerals to indicate their value (units, tens, hundreds, and so on).
An identified risk factor for osteoporosis is the intake of excessive amounts of vitamin A. Dietary intake of approximately double the recommended daily amount of vitamin A, by women, has been shown to reduce bone mineral density and increase the chances for hip fractures compared with women who consumed the recommended daily amount (or less) of vitamin A.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
![(a) Feeding by bear on salmon results in large allochthonous inputs of nutrients into (b) the forest](https://biology-forums.com/gallery/47/medium_33_17_02_12_7_02_16_20341303.jpeg)
![Feedback mechanisms of the thyroid gland: (1) stimulus; (2) release of TSH; (3) release of thyroid h](https://biology-forums.com/gallery/47/medium_46687_29_12_14_8_33_50_19766545.jpeg)