Birgitta Tullberg was a professor of evolutionary ecology. She was one of Sweden’s leading researchers in the crossover between evolutionary ecology, behavioural ecology and human ethology. She was also a vital link in the chain of prominent researchers and ambassadors of the biological sciences.

Birgitta Tullberg was born Anna Birgitta Sillén in 1952. She grew up in Djursholm. Her mother, Birgit Sillén, was an artist and her father, Lars Gunnar Sillén, was a professor of inorganic chemistry at Kungliga Tekniska Högskolan (royal institute of technology) in Stockholm. She had three brothers, two of whom were older than she whilst the third was her junior. Birgitta Tullberg focused on developing an academic career and, given her serious interest in animals and nature, she initially studied zoology. The Stockholm University zoology department had a lengthy tradition of anatomical studies but, in the early 1970s just when Birgitta Tullberg was starting her studies, a change occurred placing the new disciplines of ecology and ethology in focus. Thus, instead of studying animal remains through skeletal and bone fragments the focus now transferred onto living animals and their behaviour both in laboratory conditions and in the wild.

After gaining her Bachelor’s degree in chemistry and biology Birgitta Tullberg was taken on as a PhD candidate. Following a somewhat convoluted start to her research she gained her PhD in 1982 through a dissertation entitled Behavioural ecology and population dynamics of an aposematic seed bug, Lygaeus equestris. One of the dissertation essays in particular underpinned her future research, eventually bringing her to international attention. The essay had shown that Black-and-Red-bugs (Lygaeus equestris), which were both unappetising to their predators and displayed a conspicuous black, red, and white colouration, tended to survive attacks by predators.

Although this phenomenon – that unappetising insects can defend themselves against predators – had already been discovered in the mid-1800s, it only became a really popular subject over a century later upon the realisation that this gave rise to a problem: how then did warning colouration evolve? The dominant thought had been that predators had to “learn” through their own experiences that brightly-coloured insects could be inedible or poisonous. It was assumed that the first member of a group which displayed warning colouration was eaten. The question thus remained as to how such an altruistic property could have developed as part of natural selection. The solution offered was that evolution must depend on so-called kin selection – even if the altruistic individual member of a species sacrificed itself it did so for the benefit of its fellow members. It was generally known that many insects which display warning colouration live in groups, such as the Black-and-Red-bugs that Birgitta Tullberg studied. In the autumn they gather in their thousands prior to hibernating, often close to prominent landmarks such as churches. The monarch butterfly, for example, hibernates in large colonies which can comprise more than one hundred million individuals.

Once Birgitta Tullberg discovered that insects which displayed warning colouration can often survive being attacked she could not accept the dominant belief that kin selection was a necessary aspect of the evolution of these warning colours. She, instead, felt that warning colouration may perhaps have developed through individual selection. These were two competing ideas – either living in a large group had come about first and pre-dated the evolution of warning colouration or warning colouration evolved before the habit of living in a colony arose. Birgitta Tullberg realised that phylogenetic analysis could resolve this conflict and thus she began to collate information from several thousand species of butterfly, all displaying great variations: some types include larvae which live in groups and are camouflaged, others include larvae which live in groups but display warning colouration, and still others include larvae that live separately and are camouflaged and the final group comprise larvae which live separately but display warning colouration. Birgitta Tullberg’s analysis of these four combinations revealed that in several instances the display of warning colouration in butterfly larvae had developed amongst those that lived separately and the need to live in colonies had only arisen subsequently. She never found a single case where the need to live in groups preceded the display of warning colouration. Birgitta’s article published in the Evolution journal in 1988 concluded by stating that kin selection was of little to no importance in the evolution of warning colouration.

Birgitta Tullberg’s essay was a pioneering work in what is now known as “trädtänkande” (tree-thinking) where phylogenetic analysis enables the deduction of the order in which various characteristics developed. The essay also represented a genuine scientific breakthrough. Birgitta Tullberg subsequently successfully adapted the methodology by studying several other animal groups, from fish and birds to mammals, including humans. An example of a heavily cited work, in which she adapted evolutionary biology theory to her studies of anthropoid primates (of which humans are one of 68 species), is her 1983 work entitled The relationship between concealed ovulation and mating systems in anthropoid primates: a phylogenetic analysis. In this piece Birgitta Tullberg analysed the connection between hidden ovulation and a monogamous or polygamous mating system. Her analysis revealed that there is a clear connection between hidden ovulation and monogamy whilst it was also clear that hidden ovulation tends to lead to the evolution of monogamy rather than the opposite, namely that monogamy leads to hidden ovulation.

Birgitta Tullberg was also interested in how the evolution of human behaviour relates to normative ethics – this is a subject that is more conceptual than empirical and seeks to answer the question of how norms can be related to human behaviour within an evolutionary biology perspective. She collaborated with her husband, Jan Tullberg, on this subject and together they published a book entitled Naturlig etik: en uppgörelse med altruismen, in 1994. They both also participated in several public debates during the later 1990s and the ensuing decades.

Birgitta Tullberg was an excellent lecturer and participated in public debates with great courage and integrity on a variety of topics, not least the issue of the place of the wolf within Sweden’s natural world – an issue which remains controversial and in which obvious wildlife concerns are opposed to a more hard-to-define group of what one could call the anti-wolf faction. At her own department Birgitta Tullberg was much loved not just as a teacher of ecology, ethology, and evolutionary biology, but also as tutor of post-graduates. Throughout her more than thirty year career she guided many research students towards completing their PhDs.

Along with her scientific success Birgitta Tullberg also held many honorary roles. She was a member of Naturvetenskapliga forskningsrådets biologikommitté (natural sciences research council biology committee), a member of Naturhistoriska riksmuseets board, a member of the Nordic Oikos society, and in 2010 she was elected as a member of the Royal Swedish Academy of Sciences, for which she was active on several committees and advisory committees. In 2013 she was elected as prefect of Stockholm university’s zoology department, a position she retained until she died.

Birgitta Tullberg died in 2017. She is buried at Galärvarvskyrkogården (cemetery) in Stockholm.