Forscher verändert die Gene von menschlichen Zwillingen mittels Crispr

Ein Chinesischer Forscher gibt an, dass er genetische Veränderungen an Menschen vorgenommen hat:

Angesichts scharfer weltweiter Kritik hat der chinesische Forscher He Jiankui seine Arbeit verteidigt, die zur Geburt der weltweit ersten genetisch veränderten Babys geführt haben soll. Die Wissenschaft müsse mehr tun, um Menschen mit Krankheiten zu helfen, sagt He am Mittwoch auf einem Genomforscher-Kongress in Hongkong, bei dem er sich den Fragen aufgebrachter internationaler Experten stellte.

(….)

In Hongkong wiederholte He, dass er insgesamt mehrere kinderlose Paare aus gesunder Mutter und HIV-infiziertem Vater dazu brachte, bei den Versuchen mitzumachen. Am Ende habe eines der Paare Zwillinge bekommen. „Auf diesen speziellen Fall bin ich wirklich stolz“, sagte He. Nach der Geburt der Kinder habe er vom Vater eine Nachricht erhalten, in der dieser versprach, hart zu arbeiten, Geld zu verdienen und sich immer um seine beiden Töchter und seine Frau zu kümmern.

Nach Ansicht des Nobelpreisträgers David Baltimore ist der Fall ein Beleg für mangelnde Selbstkontrolle in der Wissenschaft. Baltimore erklärte in Hongkong, die Arbeit des chinesischen Forschers müsse als unverantwortlich eingestuft werden. Baltimore erklärte, ein solches Vorgehen sei medizinisch nicht notwendig. Es verstoße außerdem gegen Vereinbarungen, die in der Wissenschaft vor einigen Jahren getroffen worden seien. Der Nobelpreisträger kündigte an, ein Ausschuss der Konferenz werde am Donnerstag eine Stellungnahme zur Zukunft des Fachgebiets veröffentlichen.

Die Welt ist empört, weil genau das eben eine Tabu sein soll. Warum aber eigentlich?

Auf der einen Seite könnten sich ungeahnte Vorteile ergeben. Etwa eine ganz besonders hohe Intelligenz, die Immunität gegen bestimmte Krankheiten oder schlicht einen kräftigeren Menschen (damit wir endlich Supersoldaten haben).

Auf der Kontraseite werden erhebliche Risiken darin gesehen, dass man mit der Veränderung ungeahnte Folgen erzeugen kann, dass Menschen eben keine Versuchstiere sind und es unwürdig ist, sie als Testwesen zu benutzen und auch der Gedanke, dass man damit „bessere“ Menschen schaffen könnte, die dann letztendlich zu Unfrieden führen, eine Teilung in die verbesserte und die unverbesserte Menschheit.

Ich muss sagen, dass ich etwas gespannt wäre, was ein verrückter und skrupelloser, dafür aber genialer Forscher mit einem geheimen Untergrundlabor aus der Menschheit so heraus holen könnte. Vielleicht brauchen wir ein paar genmanipulierte Supergehirne, die uns in allen möglichen Bereichen voranbringen. Immerhin ist die menschliche Fortpflanzung auch einfacher zu kontrollieren als die Ausbreitung von genetisch veränderten Pflanzen.

Um so mehr wir vom Menschen und seinen Genen verstehen, um so besser die Methoden werden, um so höher wird die Versuchung sein, die Methoden auch bei Menschen anzuweden. Und vielleicht sind sie auch bald ganz normal.

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Die Wirkung von Testosteron

Der englische Wikipedia Artikel zu Testosteron gibt einen guten Überblick über die durch Testosteron bewirkten Effekte:

In general, androgens such as testosterone promote protein synthesis and thus growth of tissues with androgen receptors.[11]Testosterone can be described as having virilising and anabolic effects (though these categorical descriptions are somewhat arbitrary, as there is a great deal of mutual overlap between them).[12]

Testosterone effects can also be classified by the age of usual occurrence. For postnataleffects in both males and females, these are mostly dependent on the levels and duration of circulating free testosterone.

Before birth

Effects before birth are divided into two categories, classified in relation to the stages of development.

The first period occurs between 4 and 6 weeks of the gestation. Examples include genital virilisation such as midline fusion, phallic urethrascrotal thinning and rugation, and phallic enlargement; although the role of testosterone is far smaller than that of dihydrotestosterone. There is also development of the prostate gland and seminal vesicles.

During the second trimester, androgen level is associated with sex formation.[13] This period affects the femininization or masculinization of the fetus and can be a better predictor of feminine or masculine behaviours such as sex typed behaviour than an adult’s own levels. A mother’s testosterone level during pregnancy is correlated with her daughter’s sex-typical behavior as an adult, and the correlation is even stronger than with the daughter’s own adult testosterone level.[14]

Early infancy

Early infancy androgen effects are the least understood. In the first weeks of life for male infants, testosterone levels rise. The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by 4–7 months of age.[15][16] The function of this rise in humans is unknown. It has been theorized that brain masculinizationis occurring since no significant changes have been identified in other parts of the body.[17]The male brain is masculinized by the aromatization of testosterone into estrogen, which crosses the blood–brain barrier and enters the male brain, whereas female fetuses have α-fetoprotein, which binds the estrogen so that female brains are not affected.[18]

Before puberty

Before puberty effects of rising androgen levels occur in both boys and girls. These include adult-type body odor, increased oiliness of skin and hair, acnepubarche(appearance of pubic hair), axillary hair(armpit hair), growth spurt, accelerated bone maturation, and facial hair.[19]

Pubertal

Pubertal effects begin to occur when androgen has been higher than normal adult female levels for months or years. In males, these are usual late pubertal effects, and occur in women after prolonged periods of heightened levels of free testosterone in the blood. The effects include:[19][20]

Growth of spermatogenic tissue in testicles, male fertilitypenis or clitoris enlargement, increased libido and frequency of erection or clitoral engorgement. Growth of jaw, brow, chin, nose, and remodeling of facial bone contours, in conjunction with human growth hormone.[21] Completion of bone maturation and termination of growth. This occurs indirectly via estradiol metabolites and hence more gradually in men than women. Increased muscle strength and mass, shoulders become broader and rib cage expands, deepening of voice, growth of the Adam’s apple. Enlargement of sebaceous glands. This might cause acne, subcutaneous fat in face decreases. Pubic hair extends to thighs and up toward umbilicus, development of facial hair (sideburnsbeardmoustache), loss of scalp hair (androgenetic alopecia), increase in chest hair, periareolar hair, perianal hair, leg hairarmpit hair.

Adult

Testosterone is necessary for normal spermdevelopment. It activates genes in Sertoli cells, which promote differentiation of spermatogonia. It regulates acute HPA (hypothalamic–pituitary–adrenal axis) response under dominance challenge.[22]Androgen including testosterone enhances muscle growth. Testosterone also regulates the population of thromboxane A2 receptors on megakaryocytes and platelets and hence platelet aggregation in humans.[23][24]

Adult testosterone effects are more clearly demonstrable in males than in females, but are likely important to both sexes. Some of these effects may decline as testosterone levels might decrease in the later decades of adult life.[25]

Health risksEdit

Testosterone does not appear to increase the risk of developing prostate cancer. In people who have undergone testosterone deprivation therapy, testosterone increases beyond the castrate level have been shown to increase the rate of spread of an existing prostate cancer.[26][27][28]

Conflicting results have been obtained concerning the importance of testosterone in maintaining cardiovascular health.[29][30]Nevertheless, maintaining normal testosterone levels in elderly men has been shown to improve many parameters that are thought to reduce cardiovascular disease risk, such as increased lean body mass, decreased visceral fat mass, decreased total cholesterol, and glycemic control.[31]

High androgen levels are associated with menstrual cycle irregularities in both clinical populations and healthy women.[32]

Sexual arousalEdit

When testosterone and endorphins in ejaculated semen meet the cervical wall after sexual intercourse, females receive a spike in testosterone, endorphin, and oxytocin levels, and males after orgasm during copulation experience an increase in endorphins and a marked increase in oxytocin levels. This adds to the hospitable physiological environment in the female internal reproductive tract for conceiving, and later for nurturing the conceptus in the pre-embryonic stages, and stimulates feelings of love, desire, and paternal care in the male (this is the only time male oxytocin levels rival a female’s).[citation needed]

Testosterone levels follow a nyctohemeral rhythm that peaks early each day, regardless of sexual activity.[33]

There are positive correlations between positive orgasm experience in women and testosterone levels where relaxation was a key perception of the experience. There is no correlation between testosterone and men’s perceptions of their orgasm experience, and also no correlation between higher testosterone levels and greater sexual assertiveness in either sex.[34]

Sexual arousal and masturbation in women produce small increases in testosterone concentrations.[35] The plasma levels of various steroids significantly increase after masturbation in men and the testosterone levels correlate to those levels.[36]

Mammalian studies

Studies conducted in rats have indicated that their degree of sexual arousal is sensitive to reductions in testosterone. When testosterone-deprived rats were given medium levels of testosterone, their sexual behaviors (copulation, partner preference, etc.) resumed, but not when given low amounts of the same hormone. Therefore, these mammals may provide a model for studying clinical populations among humans suffering from sexual arousal deficits such as hypoactive sexual desire disorder.[37]

In every mammalian species examined demonstrated a marked increase in a male’s testosterone level upon encountering a novelfemale. The reflexive testosterone increases in male mice is related to the male’s initial level of sexual arousal.[38]

In non-human primates, it may be that testosterone in puberty stimulates sexual arousal, which allows the primate to increasingly seek out sexual experiences with females and thus creates a sexual preference for females.[39] Some research has also indicated that if testosterone is eliminated in an adult male human or other adult male primate’s system, its sexual motivation decreases, but there is no corresponding decrease in ability to engage in sexual activity (mounting, ejaculating, etc.).[39]

In accordance with sperm competition theory, testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats.[40]This reaction engages penile reflexes (such as erection and ejaculation) that aid in sperm competition when more than one male is present in mating encounters, allowing for more production of successful sperm and a higher chance of reproduction.

Males

In men, higher levels of testosterone are associated with periods of sexual activity.[41]Testosterone also increased in heterosexual men after having had a brief conversation with a woman. The increase in testosterone levels was associated with the degree that the women thought the men were trying to impress them.[42]

Men who watch a sexually explicit movie have an average increase of 35% in testosterone, peaking at 60–90 minutes after the end of the film, but no increase is seen in men who watch sexually neutral films.[43] Men who watch sexually explicit films also report increased motivation, competitiveness, and decreased exhaustion.[44] A link has also been found between relaxation following sexual arousal and testosterone levels.[45]

Men’s levels of testosterone, a hormone known to affect men’s mating behaviour, changes depending on whether they are exposed to an ovulating or nonovulating woman’s body odour. Men who are exposed to scents of ovulating women maintained a stable testosterone level that was higher than the testosterone level of men exposed to nonovulation cues. Testosterone levels and sexual arousal in men are heavily aware of hormone cycles in females.[46] This may be linked to the ovulatory shift hypothesis,[47]where males are adapted to respond to the ovulation cycles of females by sensing when they are most fertile and whereby females look for preferred male mates when they are the most fertile; both actions may be driven by hormones.

Females

Androgens may modulate the physiology of vaginal tissue and contribute to female genital sexual arousal.[48] Women’s level of testosterone is higher when measured pre-intercourse vs pre-cuddling, as well as post-intercourse vs post-cuddling.[49] There is a time lag effect when testosterone is administered, on genital arousal in women. In addition, a continuous increase in vaginal sexual arousal may result in higher genital sensations and sexual appetitive behaviors.[50]

When females have a higher baseline level of testosterone, they have higher increases in sexual arousal levels but smaller increases in testosterone, indicating a ceiling effect on testosterone levels in females. Sexual thoughts also change the level of testosterone but not level of cortisol in the female body, and hormonal contraceptives may affect the variation in testosterone response to sexual thoughts.[51]

Testosterone may prove to be an effective treatment in female sexual arousal disorders,[52] and is available as a dermal patch. There is no FDA approved androgen preparation for the treatment of androgen insufficiency; however, it has been used off-label to treat low libido and sexual dysfunction in older women. Testosterone may be a treatment for postmenopausal women as long as they are effectively estrogenized.[52]

Romantic relationships

Falling in love decreases men’s testosterone levels while increasing women’s testosterone levels. There has been speculation that these changes in testosterone result in the temporary reduction of differences in behavior between the sexes.[53] However, it is suggested that after the „honeymoon phase“ ends—about four years into a relationship—this change in testosterone levels is no longer apparent.[53] Men who produce less testosterone are more likely to be in a relationship[54] or married,[55] and men who produce more testosterone are more likely to divorce;[55] however, causality cannot be determined in this correlation. Marriage or commitment could cause a decrease in testosterone levels.[56] Single men who have not had relationship experience have lower testosterone levels than single men with experience. It is suggested that these single men with prior experience are in a more competitive state than their non-experienced counterparts.[57] Married men who engage in bond-maintenance activities such as spending the day with their spouse/and or child have no different testosterone levels compared to times when they do not engage in such activities. Collectively, these results suggest that the presence of competitive activities rather than bond-maintenance activities are more relevant to changes in testosterone levels.[58]

Men who produce more testosterone are more likely to engage in extramarital sex.[55]Testosterone levels do not rely on physical presence of a partner; testosterone levels of men engaging in same-city and long-distance relationships are similar.[54] Physical presence may be required for women who are in relationships for the testosterone–partner interaction, where same-city partnered women have lower testosterone levels than long-distance partnered women.[59]

Fatherhood

Fatherhood also decreases testosterone levels in men, suggesting that the resulting emotional and behavioral changes promote paternal care.[60] The way testosterone levels change when a child is in distress is indicative of fathering styles. If the levels reduce, then there is more empathy by the father than in fathers whose levels go up.[61]

Motivation

Testosterone levels play a major role in risk-taking during financial decisions.[62][63]

Aggression and criminality

Most studies support a link between adult criminality and testosterone, although the relationship is modest if examined separately for each sex. Nearly all studies of juvenile delinquency and testosterone are not significant. Most studies have also found testosterone to be associated with behaviors or personality traits linked with criminality such as antisocial behavior and alcoholism. Many studies have also been done on the relationship between more general aggressive behavior/feelings and testosterone. About half the studies have found a relationship and about half no relationship.[64]

Testosterone is only one of many factors that influence aggression and the effects of previous experience and environmental stimuli have been found to correlate more strongly. A few studies indicate that the testosterone derivative estradiol (one form of estrogen) might play an important role in male aggression.[64][65][66][67] Studies have also found that testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus.[68]

The sexual hormone can encourage fair behavior. For the study subjects took part in a behavioral experiment where the distribution of a real amount of money was decided. The rules allowed both fair and unfair offers. The negotiating partner could subsequently accept or decline the offer. The fairer the offer, the less probable a refusal by the negotiating partner. If no agreement was reached, neither party earned anything. Test subjects with an artificially enhanced testosterone level generally made better, fairer offers than those who received placebos, thus reducing the risk of a rejection of their offer to a minimum. Two later studies have empirically confirmed these results.[69][70][71]However men with high testosterone were significantly 27% less generous in an ultimatum game.[72] The Annual NY Academy of Sciences has also found anabolic steroid use which increase testosterone to be higher in teenagers, and this was associated with increased violence.[73] Studies have also found administered testosterone to increase verbal aggression and anger in some participants.[74]

Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.[75] The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.[75]Thus it is the challenge of competition among males of the species that facilitates aggression and violence.[75] Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.[75] The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males.[75]

The second theory is similar and is known as „evolutionary neuroandrogenic (ENA) theory of male aggression“.[76][77] Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.[76] The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.[78] Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.[79][80][81][82][83]

The rise in testosterone levels during competition predicted aggression in males but not in females.[84] Subjects who interacted with hand guns and an experimental game showed rise in testosterone and aggression.[85] Natural selection might have evolved males to be more sensitive to competitive and status challenge situations and that the interacting roles of testosterone are the essential ingredient for aggressive behaviour in these situations.[86] Testosterone produces aggression by activating subcortical areas in the brain, which may also be inhibited or suppressed by social norms or familial situations while still manifesting in diverse intensities and ways through thoughts, anger, verbal aggression, competition, dominance and physical violence.[87] Testosterone mediates attraction to cruel and violent cues in men by promoting extended viewing of violent stimuli.[88] Testosterone specific structural brain characteristic can predict aggressive behaviour in individuals.[89]

Estradiol is known to correlate with aggression in male mice.[90] Moreover, the conversion of testosterone to estradiol regulates male aggression in sparrows during breeding season.[91] Rats who were given anabolic steroids that increase testosterone were also more physically aggressive to provocation as a result of „threat sensitivity“.[92]

Brain

The brain is also affected by this sexual differentiation;[13] the enzyme aromataseconverts testosterone into estradiol that is responsible for masculinization of the brain in male mice. In humans, masculinization of the fetal brain appears, by observation of gender preference in patients with congenital diseases of androgen formation or androgen receptor function, to be associated with functional androgen receptors.[93]

There are some differences between a male and female brain (possibly the result of different testosterone levels), one of them being size: the male human brain is, on average, larger.[94] Men were found to have a total myelinated fiber length of 176,000 km at the age of 20, whereas in women the total length was 149,000 km (approx. 15% less).[95]

No immediate short term effects on mood or behavior were found from the administration of supraphysiologic doses of testosterone for 10 weeks on 43 healthy men.[96] A correlation between testosterone and risk tolerance in career choice exists among women.[62][97]

Attention, memory, and spatial ability are key cognitive functions affected by testosterone in humans. Preliminary evidence suggests that low testosterone levels may be a risk factor for cognitive decline and possibly for dementia of the Alzheimer’s type,[98][99][100][101] a key argument in life extension medicine for the use of testosterone in anti-aging therapies. Much of the literature, however, suggests a curvilinear or even quadratic relationship between spatial performance and circulating testosterone,[102]where both hypo- and hypersecretion (deficient- and excessive-secretion) of circulating androgens have negative effects on cognition.

 

Religion als gutes Meme

Als Atheist und jemand, der davon ausgeht, dass die Evolutionstheorie keinen Raum für einen Gott lässt, der die Welt und den Menschen geschaffen hat, und der auch davon ausgeht, dass alle „Wunder“ eine rationale Erklärung haben, würde ich dennoch vertreten, dass Religion häufig sehr gute Memes bietet.

Damit meine ich nicht entsprechende Bilder sondern eher etwas auf der Grundlage der Memetheorie von Dawkins:

Religionen passen sehr zu unserem Denken und sind damit sehr verführerisch, was ihnen eine hohe Haltbarkeit gibt.

Zum einen geben einem Religionen einen festen Halt, ein Gut und Böse, wobei das Gute meist auf der eigenen Seite ist, wenn man nicht einer Religion folgt, die weniger auf Moral als auf Macht abstellt, die dann auch aus der „Bösen“ Seite folgen kann (aber natürlich damit gerechtfertigt werden kann, dass man überlegen ist).

Sie bedient häufig unser Bedürfnis Gründe zu erkennen, Sachen einen Sinn zu geben, sie erlaubt ein Verhandeln und Zwigespräche, wenn es eigentlich nichts zu verhandeln gibt („Bitte Gott, lass mich diese Klausur bestanden haben, dann werde ich in Zukunft ein guter Mensch sein.“)

Sie ordnet einen in eine Hierarchie ein, in der man über anderen steht, aber gleichzeitig auch einen „guten Herrscher“ hat, der an dem wohl von einem interessiert ist. Früher mögen sie auch die Bildung einer einheitlichen Meinung erleichtert haben und Regeln absolut gesetzt haben und Strafen für einen Verstoß gegeben haben, eine Instanz, die alles sieht und Fehlverhalten teuer macht. Dieser Prozess spielt denke ich in der heutigen Welt häufig eine geringere Rolle, aber im persönlichen mag die Vorstellung vielen helfen solches Verhalten für sie selbst lohnender zu machen und sich gut dabei zu fühlen.

Sie erlauben zudem ein gewisses Gemeinschaftsgefühl zu erzeugen.

Momentan treten immer mehr Funktionen von Gott zurück, weil die Wichtigkeit verschiedener Memes in ihrer Funktion zurückgeht. Wir haben eine vergleichsweise sichere Welt, die ihre eigenen Regeln vorgibt und umsetzen kann, ohne das wir einen strafenden Gott glauben.

Aber auch viele Atheisten werden in passenden Stunden schon mal den Gedanken an einen „Handel“ im Kopf gehabt haben, ein „Lass das gut gehen und ich werde dann was für dich/die Gesellschaft  tun“ an eine imaginäre Person oder ins nichts gesprochen. Es beruhigt einen vielleicht einfach, wenn man das Gefühl hat, dass man da noch etwas machen kann, dass es dann irgendwie ja gut gehen muss, weil man ja auch ein Gegenangebot dafür gemacht hat.

Das bedeutet nicht, dass ich Religionen plötzlich gut finde. Es erklärt aber, warum der Gedanke an etwas Übergeordnetes eine hohe Widerstandskraft hat

 

Gibt es Homophobie nur beim Menschen?

Kürzlich wurde hier die These aufgestellt, dass lediglich der Mensch homophob sein kann, um so zu belegen, dass es eine kulturelle Sache ist.

Wäre Homophobie evolutionär oder sonstwie biologisch erklärbar, müsste es sie auch bei Tieren geben. Aber der Mensch ist das einzige Tier, das Homophobie zeigt. Sie kann daher nur kulturell bedingt sein.

Sicherlich ist ein großer kultureller Anteil dabei, wie man auf Homosexualität reagiert, das ist aus meiner Sicht aber unabhängig davon, dass sie dennoch einen gewissen biologischen Anteil haben kann. 

Aber ich finde dennoch die These, dass nur Menschen Homophobie kennen interessant, weil sie einen zu der Frage bringt: Wie würden denn Tiere überhaupt Homophobie deutlich machen?

Ich hatte entsprechend kommentiert:

Wie verhalten sich denn Tiere üblicherweise gegen homosexuellen Tieren?
Wie reagiert ein Hetero-Schimpanse darauf, dass ein Homosexueller männlicher Schimpanse mit ihm Sex haben will?
Wie reagieren Hetero-Schimpansen darauf, dass ein männlicher Schimpanse eher weiblich verhält? Ich vermute mal, er wird da schnell ganz unten in der Hierarchie stehen
Ich vermute ein Hetero-Gorilla würde bei einen Homo-Gorilla auch nicht sagen: „Oh du bist ja Homosexuell, da willst du mir ja gar nicht meinen Harem wegnehmen, dann verkloppe ich dich ausnahmsweise mal nicht, wie sonst alle Männchen“

Jetzt wäre Homophobie sicherlich nicht nur die Reaktion auf den Versuch Sex zu haben, aber ich vermute mal, dass ein entsprechender Schimpanse auch eher niedriger in der Hierarchie stehen könnte, weil er sich in seinen versuchen, sich zu paaren, mit zu vielen anderen Affen anlegt. Vielleicht käme es auch dort auf die „Kultur“ an.

Ich finde es daher gar nicht so einfach festzustellen, dass es Homophobie nur beim Menschen gibt.

Es ist aber eine dieser Aussagen, die nach einem tollen Argument klingen, die aber tatsächlich eher nicht sehr gut abgesichert sind und leicht zu hinterfragen sind.