After torrential rains, butterflies always flock to the mud puddles in Pigeon Mountain in northwestern Georgia. James Adams and Owen Finkelstein quietly ambush with nets. Suddenly, a very strange butterfly flew past the two of them. Its left wing is yellow, and its right wing is black, as if someone had torn two different butterflies in half and spliced them together perfectly. Finkelstein couldn’t help but cried out. James suppressed his inner excitement and caught it after a few steps. James immediately realized that he had just caught a hermaphrodite butterfly-a half-female and half-male creature.
Butterfly collectors love hermaphrodite butterflies because they are rare and special. They are unexpected works in the symmetrical movement created by the creator. Scientists also love hermaphrodite butterflies because they provide excellent examples for the study of females, males, and hermaphrodites.
For hundreds of years, biologists have been recording the hermaphrodite creatures they found, including insects, spiders, lobsters, and birds. In recent years, researchers have overturned the traditional theory of gender formation through the use of sophisticated experimental methods and studies on hermaphrodite organisms. Both reality and the history of science have proven that these creatures seem weird, peculiar, and asymmetric, and cannot be classified into any biological category, but they can best reveal the growth pattern of creatures. Such a conclusion does not come from scientists’ research on a large number of normal birds, but from research on a very small number of hermaphrodite birds.
It all starts with a zebra finch.
Bird eggs in a male birdcage
At the end of the 20th century, a breeder in the Rockefeller University laboratory discovered that one after another bird eggs appeared in a cage containing only male zebra finches. In order to find the “culprit”, the breeder moved them into separate bird cages for observation and found that the eggs came from a very special bird. This little bird is very different from other zebra finches. Seen from the right, it has all the characteristics of a male zebra finch: orange feathers on the cheeks, zebra stripes on the neck, and beautiful brown wings with white spots. From the left side, it is a typical female zebra finch: almost all gray feathers, a few black and white markings on the face, and a light yellow breast. The head of this ornithological laboratory is a neuroscientist at Rockefeller University named Fernando Notteboom. When he realized that this particular bird was hermaphrodite, he gave the bird to Art Arnold, his former student at UCLA. He believes that Arnold mainly studies gender differences, and perhaps something can be learned from this bird.
For a long time, scientists believed that the sex formation process of birds is the same as that of mammals. At first, a bird is just a genderless embryo. Later, under the dominance of the sex chromosomes, the bird grows a pair of testes or ovaries. The hormones released from the testicles or ovaries will encourage the birds to continue to grow according to certain gender characteristics. However, some later studies seem to indicate that this interpretation version is too simple.
Following this clue, Arnold and his colleagues decided to conduct an in-depth study of the brain cells of this zebra finch. Generally speaking, the neural circuit network in the brain of male zebra finches is designed to learn courtship songs and is much larger than the same area of females. If sex formation is mainly determined by hormones, then the left and right sides of the brain of this androgynous bird should have similar structures. After all, the hermaphrodite sex hormones released from the testicles or ovaries should be distributed throughout the various organs in the body.
However, Arnold’s research team found that the love song learning area in the right half of the zebra finch’s brain was 82% larger than the left half. For further research, the researchers sliced their brains and immersed them in a solution filled with radioactive ribonucleic acid. These radioactive ribonucleic acids would be adsorbed on one of the Z or W sex chromosomes. After placing it on the photosensitive plate, the scientists found that the right hemisphere of the brain was filled with male cells composed of two Z chromosomes, while the left hemisphere was filled with female cells containing both Z and W chromosomes. This means that sex chromosomes, not hormones, dominate the fate of every cell in the brain. Arnold said: “That hermaphroditic bird overturned some of the so-called classic scientific understandings in my mind. Brain cell tissue is not a whiteboard that allows hormones to write. It has been set before the organism is born.”
Sex chromosome change cell
2005 Around the year, Mike Clinton, a developmental biologist at the University of Edinburgh, began to collect and study hermaphroditic chickens from farms around Britain. Seen from one side, these chickens are male, with white and golden feathers, large red wattles on the lower jaw, and long horn-like spines on the legs; from the other side, it looks like a female again, with tan feathers and lower jaws. The lobes and the long spines on the legs are also much smaller. Clinton’s research team tested DNA in the blood, skin, and muscle cells of hermaphroditic chickens. They found that hermaphrodite chickens not only show two types in appearance, just like the previous zebra finch, at the cellular level, the whole body can basically be divided into two different types-a large number of ZW females. The cells are on one side, and the ZZ male cells are on the other side, but some have both types of cells. It’s like a separate bottle containing two flavors of jelly beans, most of them are separated, and a small amount will be mixed together.
These hermaphrodite organisms confirmed that the sex of birds is formed through cell-by-cell changes, and is not formed under the uniform influence of hormones like mammals. However, it is not yet clear how the sex chromosomes in each cell protect the formation of sex from hormones. Perhaps, from the moment of fertilization, the ZW chromosome combination has begun to cause a certain change in the expression of genes-allowing the molecules surrounding the DNA to promote or inhibit its various activities. Clinton and his colleagues found that normally developing female or male bird embryos have grown according to different genetic patterns before their sexual organs are formed.
Sex mammals form
now, Arnold and his team wanted to know whether they come in bird study conclusion also applies to mammals. In order to determine the role of hormones and chromosomes in mammalian sex formation, Arnold’s team has been studying some special mice-although they are genetically male, some have particularly many X or Y chromosomes. The release of female hormones. Arnold hopes that his research can provide new solutions to some human diseases, because the incidence and severity of many sclerosis, cancer, heart disease and other diseases have a specific gender orientation. Arnold said: “If we can figure out why a certain gender is protected during the development of the disease, we can find new treatments. To solve this problem, we need to know the various factors that determine gender differences. In the past, We have always thought that hormones are the only factor that determines gender differences. ”
Many sclerosis, such as a severe sclerosis in which the nervous system is attacked and destroyed by the immune system, is more common in female patients, but once they become ill, male patients worsen The speed will be faster. Arnold’s research on special mice that are genetically male but release female hormones shows that in the face of the same disease, the combination of XY chromosomes (rather than hormones) makes cells more vulnerable to attack.
Research on hermaphrodite zebra finches and hermaphroditic chickens has shocked researchers in other fields. Nippam Patel, a biological growth scientist at the University of California, Berkeley, said: “With regard to the question of how vertebrate cells acquire their sex, androgynous organisms have indeed subverted people’s long-held thinking.”
In addition to these studies, Patel’s research on the unique androgynous butterfly also changed people’s deep-rooted concepts. After more than ten years of painstaking research, Patel believes that in some cases, a hermaphroditic organism is not just an organism with both female and male organs, but a fusion of two types of organisms.
Many scientists attribute the appearance of hermaphrodite butterflies to errors in cell division. Like birds, male butterflies contain two Z chromosomes in each cell, while female butterflies have one Z and one W chromosome. According to the traditional interpretation theory, when a caterpillar begins to metamorphose, the dividing cells that eventually form hermaphrodite wings will also divide its chromosomes, so that one of them gets a Z and a W chromosome and becomes a female, and the other gets two Zs. Chromosomes and become males. These two daughter cells will grow into the left and right wings of the butterfly. Therefore, the butterfly will have a hermaphroditic appearance bounded by the midline.
Another hermaphrodite butterfly
scientists clearly illustrates this process, but Patel collected some pictures that he believes there is another reason to produce hermaphrodite. Every once in a while, Patel would encounter a strange butterfly. This butterfly is colorful, and the male and female appearances look very similar. Patel was able to find the hermaphrodite among them because the abdomen of the hermaphrodite butterfly is slightly different in size and structure-there are female and male genitalia on the left and right sides of the abdomen.
So Patel thought that in addition to being hermaphrodite, they might also be a hybrid. The different patterns on their two wings reveal their genetic differences, and this difference cannot be explained only by a mixture of male and female cells. . For example, the Optix gene is responsible for giving the hindwings of the butterfly red, the WntA gene is responsible for giving it black like a black marker, and the Z and W chromosomes do not have these two genes. The traditional explanation is that the genetic differences on both sides of the hermaphrodite only exist on the Z and W chromosomes, but their wings are also significantly different in color combination genes, which indicates that they have two completely different sets of genomes. In Patel’s view, since the difference between hermaphrodite nymphs is not only in gender characteristics, it can be regarded as a combination of male and female animals.
How did that happen? Insect egg cells actually have a smaller sister cell-polar body. The polar body is a by-product produced during the cell division process that produces egg cells. Sometimes, two sperms can divide within the egg cell and fertilize the nucleus and polar body of the egg cell at the same time, thus producing two embryos, like conjoined twins. However, the cell boundary between these two lives is not always so clear. This also explains why some hermaphrodite creatures have asymmetry in their appearance strictly based on the midline, while some are not, and there will be mosaic patterns that cross the midline. Although some experts have used the theory of double fertilization to explain the production of hermaphrodites, the information provided by Patel is one of the clearest evidence so far.
With the in-depth understanding of the genetic makeup of organisms, scientists discovered that, in fact, human beings are also diverse organisms. Basically, every cell in our body can be divided into two categories, namely the human cell group in the nucleus and the non-human cell group in the mitochondria (ie, free individual microorganisms). Billions of bacteria flood our skin and intestines, turning the human body into a kaleidoscope of microbial cell groups, and some foreign genes enter our cell groups with the help of bacteria and parasites. Hermaphrodite creatures with a mix of alternative appearances are also mirrors that reflect human diversity.