Scientists at the Florida Museum of Natural History reported in the latest issue of the online journal of the Public Library of Biology that after studying two kinds of body lice that occur in all races, it was found that although the shapes of these two kinds of body lice are almost the same, their genetic material deoxyribonucleic acid (DNA) is quite different.
Judging from the differences between them, as early as 6.5438+0.2 million years ago, they parted ways on the road of evolution, when they were parasitic on different races living in different continents.
The researchers pointed out that only direct contact such as fighting, dressing together or having sex can transfer lice from one species to another. So what is certain is that before the extinction of Homo erectus, it must have had close contact with modern people.
Some experts disagree with this conclusion. Max Planck, an expert on human evolution at the German Institute of Evolutionary Anthropology, said that the premise of this research result is that the ancestors of these two kinds of body lice lived 6.5438+0.2 million years ago, and the speculation of this era depends on the number of body lice at that time.
Therefore, if the estimate of this figure is wrong, then the conclusion of this study is also wrong. Nevertheless, scientists still point out that lice and other parasites are very useful for studying human evolution. Only when two hosts come into contact can they move from one host to another and start to reproduce.
The researchers said, "No matter what kind of evolutionary process humans have experienced, lice have recorded exactly the same historical period."
Extended data
First, the development of lice belongs to gradual metamorphosis, which is divided into three stages: egg, nymph and adult. ?
1, eggs
The lice eggs are light yellow and oval, with a length of 0.9~ 1.0mm and a cover at one end. When laying eggs, female lice hold hair or clothing fibers with their tails, secrete glue, and stick the eggs to prevent them from falling off. Both head lice and crabs lay eggs on hair, while body lice lay eggs on the fibers of clothes.
Step 2: young worms
Tick eggs hatch from eggshells after 6~8 days of development, which is called nymph. Nymphs and adults are basically similar, but they look lighter in color and smaller in size. Nymphs can suck blood as soon as they hatch, and become adults after molting for three times in about 9 days.
3. Adults
The nymph is an adult after being skinned for three times. Male and female adults can mate within 10h after the nymph is skinned for the last time, and an adult can mate several times in its life. Female insects begin to lay eggs 2 days after mating, and can produce 7~8 eggs a day. A female can lay 200~300 eggs in her lifetime.
The development from egg to adult usually takes 3~4 weeks. When the temperature is suitable (30~32 degrees Celsius) and the blood source can be obtained at any time, it only takes 16 days to complete a passage.
Second, parasitic conditions.
Lice is a kind of parasitic insect that has completely adapted to the host surface environment, and its requirements for parasitic environment are relatively constant and specific. For example, the optimum temperature of body lice is 30~32 degrees Celsius, which is the temperature of human body surface.
The optimum relative humidity is 10%~60%. Don't like humidity and high temperature. Towards darkness. Therefore, when the weather gets warmer in spring and the host sweats or has a fever due to activities, lice can easily climb out of the clothes from the body surface and spread outward through the contact of the host or clothes.
Third, blood-sucking habits
Both nymphs and adults of lice suck blood, and only human blood. The blood-sucking amount can generally reach more than 1/3 of its body weight. If you find yourself smoking, please don't pull it with brute force. Wipe the lice' heads with alcohol to loosen them. )
Baidu encyclopedia-lice
Baidu encyclopedia-lice