Hair comes in many varieties and its colour and thickness are determined by genetics, but we all have roughly the same number of hairs on our bodies.

    Hair comes in all colours, lengths, and thicknesses and it can be straight, slightly kinked, or very curly. Hair type is mostly determined by genetics, whether it is of animal, or human origin.

    Geneticists have discovered that some physical characteristics of human hair are dominant, which means that they are more likely to be passed on to children. The characteristics that are less

    likely to be passed on are called recessive.

    Dominant characteristics include curly hair, dark hair, non-red hair and recessive characteristics include straight hair, light hair, and red hair.

    So a child is more likely to inherit dark, curly hair from either parent than straight, light coloured, or red hair from either parent. Obviously, if both parents have any of these characteristics

    the odds of inheritance become much higher.

    Both men and women have a total of around 5 million hairs on their bodies. These may be dark and easy to see, or so fine that it is difficult to see them with the human eye. Even bald-headed

    people have minute hairs on their heads.

    Fair-haired people tend to have slightly more than the average and redheads slightly fewer. The only parts of the human body that are totally hairless are the lips, the palms of the hands, the

    soles of the feet, the sides of the toes and fingers and the upper part of of the ends of fingers and toes.

    Hairs are dead from the root upwards but the 100,000 or so hairs on the head grow at a rate of 10mm, or 0.4 inches per month with a slight increase during the summer months. That's an amazing 4.8

    inches per year.

    Contrary to popular belief, cutting hair does not make it grow faster, or slow it down. Thickness varies according to hair colour and redheads have thicker hair than brunettes and blondes.

    Most people lose and replace about 100 hairs per day, but hairs can remain in the same follicle for up to six years.

    Stories are often told about people finding that their hair has turned white over night when they have had a fright, or sudden shock. This is not true and what happens in these cases is that the

    coloured hair actually falls out and it leaves the white hair behind. The person may not know that they had any white hair before because it is often hidden by the coloured hair.

    頭發(fā)有許多的種類(lèi)，它的顏色及密度是由遺傳決定的，但是我們身體上毛發(fā)的數(shù)量都是大致相同的。

    頭發(fā)有不同的顏色，長(zhǎng)度及密度，它可以是直發(fā)，微卷或是大卷。不 管是動(dòng)物還是人類(lèi)，頭發(fā)的類(lèi)型絕大都是由遺傳決定的。

    遺傳學(xué)家發(fā)現(xiàn)毛發(fā)的一些物理性特征是占主導(dǎo)地位，這就意味著它是可能遺傳給下一代的。一些可能很少被遺傳的特征叫隱性特征。

    主導(dǎo)性的特征包括卷發(fā)，黑發(fā)，非紅色頭發(fā)，而隱形包括直發(fā)，稀疏毛發(fā)及紅色頭發(fā)。

    所以比起從父母那遺傳直發(fā)，稀疏毛發(fā)或紅頭發(fā)，孩子更容易遺傳父母的黑發(fā)，卷發(fā)。顯然，如果父母雙方都有任何一些這些特征，遺傳的幾率將會(huì)更大。

    不管男人還是女人，身上的毛發(fā)大概有5百萬(wàn)根。這些可能是黑色毛發(fā)，肉眼可看到的毛發(fā)，或是肉眼無(wú)法看到了毛發(fā)。甚至禿頭的人，在他的腦門(mén)上依然有細(xì)小的毛發(fā)。

    金發(fā)的人身上的毛發(fā)略多余平均數(shù)，而紅頭發(fā)的人會(huì)略少于平均數(shù)。人類(lèi)身體上完全無(wú)毛發(fā)的地方是嘴唇，手掌，腳底，腳拇指和手拇指縫及手指和腳趾的末端。

    毛發(fā)是從根部向上先死亡的，但頭上大概1萬(wàn)多的頭發(fā)在夏天大概以每月10毫米或0.4英寸的長(zhǎng)度慢慢長(zhǎng)長(zhǎng)。即每年4.8英寸的數(shù)度增長(zhǎng)。

    與大眾的想法不一樣的是，減發(fā)不會(huì)讓頭發(fā)長(zhǎng)的快或長(zhǎng)的慢。頭發(fā)稠密的不同是因?yàn)轭^發(fā)顏色的不同。紅發(fā)人的頭發(fā)會(huì)比黑發(fā)或金發(fā)的人更加稠密。

    大部分的人每天要掉100根頭發(fā)，也會(huì)重新長(zhǎng)出100根頭發(fā)，但是頭發(fā)可以保留在小發(fā)囊里長(zhǎng)達(dá)6年。

    故事中常常有說(shuō)某個(gè)人的頭發(fā)因?yàn)轶@嚇或是突然震驚而一夜間變白。這不是正確的。發(fā)生這樣的事，是因?yàn)橛蓄伾�的毛發(fā)脫落，只剩隱藏著的白發(fā)。這些人可能不知道他之前其實(shí)有白頭發(fā)的，因?yàn)橥�往白發(fā)會(huì)被有顏色頭發(fā)所掩蓋。