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The size of the eyes in mammals is relatively small; in humans, eye weight is 1% of the mass of the head, while in a starling it reaches 15%. Nocturnal animals (for example, tarsiers) and animals that live in open landscapes have larger eyes.
Diagram of a human eye; note that not all eyes have the same anatomy as a human eye. The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment. [10] The human eye is not a plain sphere but is like two spheres combined, a smaller, more sharply curved one and a larger lesser curved sphere.
Treeshrews hold about 10% of their body mass in their brain. [16] Generally speaking, the larger the animal, the smaller the brain-to-body mass ratio is. Thus, large whales have very small brains compared to their weight, and small rodents like mice have a relatively large brain, giving a brain-to-body mass ratio similar to humans. [4]
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
Compared to traditional metrics, such as the body mass index (BMI), (which uses weight and height), BRI may improve predictions of the amount of body fat and the volume of visceral adipose tissue. Despite its common use, BMI can misclassify individuals as obese because it does not distinguish between a person's lean body mass and fat mass ...
Graph showing optical density (OD) of the human crystalline lens for newborn, 30-year-old, and 65-year-old from wavelengths 300-1400 nm. Crystallins are water-soluble proteins that compose over 90% of the protein within the lens. [59] The three main crystallin types found in the human eye are α-, β-, and γ-crystallins.
An elephant's brain weighs just over 5 kg (11 lb), a bottlenose dolphin's 1.5 to 1.7 kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg (2.9 to 3.3 lb). Brain size tends to vary according to body size. The relationship is not proportional, though: the brain-to-body mass ratio varies. The largest ratio found is in the shrew. [57]
The relationship is not linear, however. Generally, small mammals have relatively larger brains than big ones. Mice have a direct brain/body size ratio similar to humans (1/40), while elephants have a comparatively small brain/body size (1/560), despite being quite intelligent animals. [18] Treeshrews have a brain/body mass ratio of (1/10). [19]