| In a 2013 book-length evaluation of the Gaia hypothesis considering modern evidence from across the various relevant disciplines, Toby Tyrrell concluded that: "I believe Gaia is a dead end. Its study has, however, generated many new and thought provoking questions. While rejecting Gaia, we can at the same time appreciate Lovelock's originality and breadth of vision, and recognise that his audacious concept has helped to stimulate many new ideas about the Earth, and to champion a holistic approach to studying it".<ref>{{citation |last=Tyrrell |first=Toby |authorlink= |date= 2013|title= On Gaia: A Critical Investigation of the Relationship between Life and Earth |url=http://press.princeton.edu/titles/9959.html |location=Princeton |publisher=Princeton University Press |page=209 |isbn=9780691121581 |accessdate= }}</ref> Elsewhere he presents his conclusion "The Gaia hypothesis is not an accurate picture of how our world works".<ref>{{Citation |last= Tyrrell |first = Toby |title =Gaia: the verdict is… |journal = New Scientist |volume = 220 |issue = 2940 |pages = 30–31 |date= 26 October 2013 |doi=10.1016/s0262-4079(13)62532-4}}</ref> This statement needs to be understood as referring to the "strong" and "moderate" forms of Gaia—that the biota obeys a principle that works to make Earth optimal (strength 5) or favourable for life (strength 4) or that it works as a homeostatic mechanism (strength 3). The latter is the "weakest" form of Gaia that Lovelock has advocated. Tyrrell rejects it. However, he finds that the two weaker forms of Gaia—Coeveolutionary Gaia and Influential Gaia, which assert that there are close links between the evolution of life and the environment and that biology affects the physical and chemical environment—are both credible, but that it is not useful to use the term "Gaia" in this sense and that those two forms were already accepted and explained by the processes of natural selection and adaptation.<ref>{{citation |last=Tyrrell |first=Toby |authorlink= |date= 2013|title= On Gaia: A Critical Investigation of the Relationship between Life and Earth |url=http://press.princeton.edu/titles/9959.html |location=Princeton |publisher=Princeton University Press |page=208 |isbn=9780691121581 |accessdate= }}</ref> | | In a 2013 book-length evaluation of the Gaia hypothesis considering modern evidence from across the various relevant disciplines, Toby Tyrrell concluded that: "I believe Gaia is a dead end. Its study has, however, generated many new and thought provoking questions. While rejecting Gaia, we can at the same time appreciate Lovelock's originality and breadth of vision, and recognise that his audacious concept has helped to stimulate many new ideas about the Earth, and to champion a holistic approach to studying it".<ref>{{citation |last=Tyrrell |first=Toby |authorlink= |date= 2013|title= On Gaia: A Critical Investigation of the Relationship between Life and Earth |url=http://press.princeton.edu/titles/9959.html |location=Princeton |publisher=Princeton University Press |page=209 |isbn=9780691121581 |accessdate= }}</ref> Elsewhere he presents his conclusion "The Gaia hypothesis is not an accurate picture of how our world works".<ref>{{Citation |last= Tyrrell |first = Toby |title =Gaia: the verdict is… |journal = New Scientist |volume = 220 |issue = 2940 |pages = 30–31 |date= 26 October 2013 |doi=10.1016/s0262-4079(13)62532-4}}</ref> This statement needs to be understood as referring to the "strong" and "moderate" forms of Gaia—that the biota obeys a principle that works to make Earth optimal (strength 5) or favourable for life (strength 4) or that it works as a homeostatic mechanism (strength 3). The latter is the "weakest" form of Gaia that Lovelock has advocated. Tyrrell rejects it. However, he finds that the two weaker forms of Gaia—Coeveolutionary Gaia and Influential Gaia, which assert that there are close links between the evolution of life and the environment and that biology affects the physical and chemical environment—are both credible, but that it is not useful to use the term "Gaia" in this sense and that those two forms were already accepted and explained by the processes of natural selection and adaptation.<ref>{{citation |last=Tyrrell |first=Toby |authorlink= |date= 2013|title= On Gaia: A Critical Investigation of the Relationship between Life and Earth |url=http://press.princeton.edu/titles/9959.html |location=Princeton |publisher=Princeton University Press |page=208 |isbn=9780691121581 |accessdate= }}</ref> |