→ instincts：inborn pattern of behavior often responsive to specific stimuli 天性
→ aberration：An aberration is an incident or way of behaving that is not typical 失常
When it comes to sexual behaviour, the animal kingdom is a broad church. Its members indulge in a wide variety of activities, including with creatures of the same sex. Flying foxes gather in all male clusters to lick each other’s erect penises. Male Humboldt squid have been found with sperm-containing sacs implanted in and around their sexual organs in similar quantities to female squid. Female snow macaques often pair off to form temporary sexual relationships that includes mounting and pelvic thrusting. Same-sex sexual behaviour has been recorded in some 1,500 animal species.
→ broad church：a group, organization, or set of beliefs which includes a wide range of different opinions or ideas 包容各種不同意見、主張的群體（或機構、信仰）;自由主義群體
→ clusters n. : a grouping of a number of similar things 群集
→ erect adj. : of sexual organs; stiff and rigid 因性刺激而勃起的
→ Humboldt squid ：洪堡烏賊，名稱源自第一個介紹該物種給西方學界的德國自然主義科學家亞歷山大·馮·洪堡。該科學家的主要成就之一就是發現物種，如洪堡企鵝，洪堡百合洪堡天竺葵等。
→ sacs n. : a structure resembling a bag in an animal 液囊
→ snow macaques：also known as snow monkeys, Japanese macaques are the world's northernmost non-human primates 雪猴
→ pelvic thrusting：The pelvic thrust is used during sexual intercourse by many species of mammals 盆腔推擠
The mainstream explanations in evolutionary biology for these behaviours are many and varied. Yet they all contain a common assumption: that sexual behaviours involving members of the same sex are a paradox that does indeed need explaining. Reproduction requires mating with a creature of the opposite sex, so why does same-sex mating happen at all?
→ paradox n. : a paradox is a statement in which it seems that if one part of it is true, the other part of it cannot be true 悖論
A paper just published in Nature Ecology and Evolution offers a different approach. Instead of regarding same-sex behaviour as an evolutionary oddity emerging from a normal baseline of different-sex behaviour, the authors suggest that it has been a norm since the first animals came into being. The common ancestor of all animals alive today, humans included, did not, they posit, have the biological equipment needed to discern the sex of others of its species. Rather, it would have exhibited indiscriminate sexual behaviour—and this would have been good enough to transmit its genes to the next generation.
→ Nature Ecology and Evolution：《自然-生態和進化科學》：《自然》雜誌1869年創刊於英國，是世界上最早的國際性科技期刊，涵蓋生命科學、自然科學、臨床醫學、物理化學等領域。自成立以來，始終如一地報導和評論全球科技領域裡最重要的突破。其辦刊宗旨是「將科學發現的重要結果介紹給公眾，讓公眾儘早知道全世界自然知識的每一分支中取得的所有進展」。
→ oddity n. : something unusual or strange 怪異；怪癖
→ posit v. : assume as a postulate 假定；假設
→ discern: detect with senses 辨別；識別
The group of young researchers from institutions across America who wrote the paper, led by Julia Monk, a graduate student at Yale, argue that conventional models of sexual behaviour’s evolution take two things for granted that they should not. The first is that the cost of same-sex behaviour is high because energy and time spent engaged in it do not contribute to reproductive success. If that were true it would indeed mean that maintenance of same sex behaviour over the generations requires some exotic explanation whereby such activity confers benefits that outweigh the disadvantage. The second assumption is that same-sex activity evolved separately in every species that exhibits it, from an ancestral population that engaged exclusively in different-sex behaviour.
Do you come here often?
Ms Monk and her co-authors question the first assumption by pointing out that many animals seem to mate at a frequency far higher than looks necessary merely to reproduce—meaning that the proportional costs of any instance of sexual activity which does not produce offspring must be low. If this is true, it reverses the burden of proof. The cost of the sensory and neurological mechanisms needed to identify another’s sex, and thus permit sex-discriminating mating behaviour, is high. Sometimes, that will be a price worth paying, especially if a long-term relationship is involved in reproduction, as it is in most birds and some mammals. But it is the evolution of sex-discrimination for which special-case exemptions must be sought, not the evolution of same-sex behaviour.
→ offspring n. : an immediate descendants of a person 後代
→ reverse v. ：turning in the opposite direction 逆轉
→ burden of proof： 舉證責任；提供證據之責
→ exemption：immunity from an obligation or duty 豁免
The second assumption is even easier to challenge. Typically, evolutionary biologists assume that traits shared widely across a related group are likely to have evolved in an ancestral population, not repeatedly and separately in each lineage. Ms Monk and her colleagues argue that cognitive biases in the subject’s practitioners have pushed them to look for fantastic explanations for the evolution of same-sex behaviours in a range of animals, rather than considering the perhaps more reasonable explanation for its persistence, that it is a low-cost ancestral trait that has little evolutionary reason to disappear.
→ traits：A trait is a particular characteristic, quality, or tendency that someone or something has 特徵
→ lineage: inherited properties shared with others of your bloodline 血統；家系
→ cognitive biases：認知偏差
Although the idea that same-sex behaviour has always been a norm is scientifically intriguing, the paper’s authors are also making a broader point about human beings』 pursuit of knowledge. Ms Monk says that the paper’s authors met through a Twitter account which promotes the work of lgbt scientists. This was a serendipitous encounter which gave them space to explore an idea that might have been dismissed at first sight in a more conventional setting. The group includes people with a range of sexual orientations, so naturally they had an incentive to ask whether mainstream evolutionary biology’s view of sexual orientation is correct.
→ intriguing adj. ：interesting or strange 新奇的；引人入勝的
→ lgbt：（lesbian Gay Bisexual Transgender）同性戀雙性戀及變性者
→ serendipitous adj. ：luckly in making unexpected and fortunate discoveries 偶然發現的
→ incentive n. : a positively motivational influence 動機；刺激
Their hypothesis still needs testing. That will mean zoologists gathering more observational data on sexual behaviour of animals in the wild—and doing so with an open mind. The authors themselves are also mulling approaches involving computer modelling, which might show that a group of organisms behaving according to their theory is capable of reaching the distribution of sexual behaviours seen in the wild today. If their hypothesis is confirmed, it raises the question of which other facets of scientific knowledge might be being obscured because the backgrounds of practitioners in those fields do not lead them to ask unconventional questions. Ms Monk’s and her colleagues』 theory may yet turn notions of the evolution of animal sexual behaviour on their head. With a broader array of minds focused on other problems, other fields might follow, too.
→ mulling v. ：reflect deeply on a subject 仔細考慮
→ array n. : an orderly arrangement 數組；列 an array of 一排；一批；大量