Over Christmas and the new year, three of the world’s leading naturalists died. Thomas Lovejoy, a conservation biologist credited with popularising the term “biodiversity” and a passionate defender of the Amazon, died on 25 December. A day later, Edward O Wilson, known to many as the “modern-day Darwin”, died in Burlington, Massachusetts. On 2 January, Richard Leakey, a world-renowned Kenyan conservationist who helped establish Africa as the birthplace of humankind, died at his home in Nairobi. From presidents to undergraduate students, thousands have paid tribute to the three men, whose achievements range from developing theories on forest and island ecosystems to reforming the Kenyan civil service and devising proposals to protect half the planet for nature. Alongside grand accomplishments, which were sometimes controversial, their passing has been a chance to reflect on the small and the mundane: fleeting interactions that inspired careers, kind words that propelled research projects, and generosity of spirit that has helped amplify the voices of those that practise and produce science. “There’s a whole generation of diverse ecologists and conservationists following in the footsteps of their work,” says Ricardo Rocha, a conservation ecologist from the island of Madeira, who studies bats and the human drivers of biodiversity loss. Holding books written by all three men, he says they all had a massive impact on his career and improved the diversity of their respective fields. “I’m black and I’m European. These were three white men that consciously and unconsciously helped promote a shift in the demographics of the scientific community.” The Guardian received dozens of responses to a callout about the legacy of Wilson, Lovejoy and Leakey. From funding field studies of indigenous territories in Peru to convincing prospective lawyers to pursue careers in human paleobiology, their impact has been far-reaching. In an email titled “Tom Lovejoy changed my life”, Alexander Nassikas explains how he switched from pursuing a career as a doctor to working on the climate crisis after visiting Camp 41 in the Amazon, where Lovejoy hosted presidents, researchers and celebrities from Tom Cruise to Olivia Newton-John. “He wrote me an email once telling me that he’s counting on me to make a difference in the world,” says Nassikas, who now works for the UN secretary general’s climate action team. Dr Dino J Martins, a renowned Kenyan entomologist and evolutionary biologist at Princeton, who heads the Mpala research centre near Mount Kenya, says his friend Leakey helped forge a path for African researchers to lead research in their own continent. “There is an entire cohort of African scientists who, against the odds, have risen because of Richard inspiring us, fighting for us and making sure we got on and did it,” he says. Dr Ben Okita-Ouma, co-chair of the world’s leading elephant conservation group, agrees. Okita-Ouma was inspired by the photo of Leakey burning ivory tusks in an anti-poaching campaign that was pinned to a noticeboard while he was at university in the early 1990s. They went on to work together at the Kenya Wildlife Service. “He loved and meant what he was doing in conservation, archeology and in dreaming big for Kenya as a nation,” says Okita-Ouma. Dr Corrie Moreau, a professor at Cornell University who founded the Women in Science group, was a student of Wilson’s at Harvard and shared his passion for ants, redrawing the insect’s family tree for her PhD dissertation. She paid tribute to his kindness and openness. Wilson, a prolific writer, wrote all his papers and books on yellow legal tablets, which were then transcribed by his assistant Kathleen Horton, who worked with him from 1965 to 2021. “Science was conducted almost exclusively by this gentleman’s club in the past. Not only did you have to look a certain way, you had to have a certain kind of background and identity,” Moreau says. “Ed saw that in order to really harness the power of our ability to understand the world around us, we had to fling open the doors and invite more people to be involved. I’m some tattooed kid from the south that was passionate about ants. That never interfered with Ed’s ability to see my intellect. That’s not true of a lot of people.” The death of all three men comes at an inflection point in the world’s ecological history. In Wilson’s final lecture in October, he reflected on the three environmental crises humanity will face this century: the climate crisis, a fresh water shortage and biodiversity loss. The new roads, infrastructure and farms that are carving up the Amazon, which Lovejoy wrote about his entire career, will dictate the fate of the world’s largest rainforest. Leakey, who was buried on his favourite ridge overlooking the Rift valley, helped ensure the African elephants and rhinos are there for future generations alongside many other achievements. Colleagues and family members say that despite rising extinctions and growing environmental destruction, Wilson, Lovejoy and Leakey remained optimistic. Lovejoy’s daughters and granddaughters paid tribute to his belief that our species would “figure it out”. For now, all three helped ensure the health of the planet remains an open question. “Giving up is a sure recipe for your worst nightmares becoming reality,” says marine biologist Elliott Norse, who, along with Wilson and Lovejoy, started using the phrase “biological diversity” around the same time in the early 1980s. “They saw bigger things in the patterns of what we do. I am eternally thankful for their contributions to our understanding of the nature of life, including the nature of humankind, and the unthinking things we are doing to our one and only home.” There were too many responses to our callout to include them all but here are a few: Tom Lovejoy was a peerless adviser because of his firm conviction that a healthy environment is the best way to provide quality of life to everyone on the planet.” Adalberto Luis Val, former director of the National Institute of Amazonian Research (INPA). Lovejoy was elected to the Brazilian Academy of Sciences shortly before his death. There will never again be anyone like Tom Lovejoy.” Primatologist Russell Mittermeier, Re:wild’s chief conservation officer, who met Lovejoy as a student at Harvard and was friends with him for half a century. Personally, Tom made it clear to me that I needed to get out more. He showed me the value of breaking out of disciplinary silos and finding partners where I didn’t think to look. He never prescribed or demanded greater breadth. He just asked the right questions at the right time for me to discover for myself the value of thinking differently. I often tell my students that if they walk into a room and know everyone already, they aren’t getting out enough.” Geoffrey Dabelko, professor at Ohio University. Lovejoy helped him start the Wilson Center’s environmental change and security programme in Washington in 1994 with PJ Simmons. The strong foundation [Leakey] laid during his tenure at KWS has helped us more than double Kenya’s elephant population to over 36,000.” Dr Patrick Omondi, former deputy head of the Kenya Wildlife Service. Leakey played a key role in listing African elephants as among the most endangered animals in the world in 1989, resulting in an international ivory trade ban. Had tropical ecologists in the 1970s-1990s deigned to ask their indigenous neighbours about the organisation and dynamics of tropical forests, we all would have made faster scientific progress.” Douglas Yu, a professor of the school of biological sciences at University of East Anglia, who, along with a colleague, was awarded a $32,000 grant in 1999 by Wilson to study Matsigenka indigenous forest classification. The study found indigenous knowledge about the Amazon was a “vast and underutilised database”. I was walking by the swimming pool in the evening before dinner when I spotted Tom Cruise. I thought that he was there shooting some movie in the Amazon. Then I saw Tom Lovejoy. He told me what he was doing, that is, to bring famous people to the Amazon to stress the global importance of protecting the forest and its immense biodiversity. I will never forget that casual and so relevant encounter with Tom. He even introduced me to Tom Cruise and some other actors as a Brazilian scientist concerned with the future of the Amazon, but certainly Tom Cruise will never remember having met me.” Carlos Nobre, a climate scientist at the University of São Paulo who co-authored articles with Lovejoy. Richard Leakey impacted so many people, whether they know it or not. People shape people and undoubtedly my time at the Turkana Basin Institute was shaped by him and countless others. It inspired me to continue on my current journey.” Kailie Batsche, PhD student at the Center for Functional Anatomy and Evolution at John Hopkins. A field trip in the Rift valley inspired her to shift from a career in law to paleoanthropology. He told me he could tell that I would do well in grad school, but also that there were still important questions in human evolution that needed to be answered and that the field needed people like me to continue to make progress and find those answers.” Sarah Baumgarten, PhD candidate in bioanthropology at Washington University, who went on the same field trip as Batsche. It was Baumgarten’s first journey outside the US and Leakey spoke with her about her future in the camp mess. We cannot stay. Entropy takes everything. Yet, although all that we have done and may yet do will be dissipated, the steps that were taken, the path of a life, forgotten or not, remain as real and eternal as the flow of time. I am made happy and feel lucky, that we have shared a goal, and above all, that our paths that have crossed, as we travel onward, on our journey to forever.” Adrian Forsyth, executive director of the Andes Amazon Fund, was a student of Wilson in the mid 1970s and worked with Lovejoy on and off for 40 years. He shared this extract from a goodbye letter he sent to Lovejoy before his death. Find more age of extinction coverage here, and follow biodiversity reporters Phoebe Weston and Patrick Greenfield on Twitter for all the latest news and features