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WORK TITLE: I, Mammal
WORK NOTES:
PSEUDONYM(S):
BIRTHDATE:
WEBSITE:
CITY: Kent
STATE:
COUNTRY: United Kingdom
NATIONALITY: British
married with two daughters
RESEARCHER NOTES:
N/A
PERSONAL
Married; wife’s name Cristina; children: Isabella, Mariana.
EDUCATION:University College London, Ph.D.
ADDRESS
CAREER
Writer and former neurobiologist. Has done research at Columbia University, New York, NY, and University College London. NeuWrite London, director.
WRITINGS
Contributor to print and online periodicals, including Nature, New Scientist, Slate, and Guardian.
SIDELIGHTS
Liam Drew, a veteran science writer and former neurobiologist, was inspired to write his first book, I, Mammal: The Story of What Makes Us Mammals, by the birth of his first child. Witnessing the birth–she was the first of his two daughters and was born prematurely–and watching her develop led him to a realization. “For twenty years, I’d studied biology; finally, I understood that I was biology,” he writes in the book. He covers the defining characteristics that define mammals and how these traits evolved, along with a history of the study of mammals and many humorous anecdotes, some drawn from his family life. “You look it up in the dictionary and it says a mammal is a warm-blooded vertebrate with hair and mammary glands, maybe a few other traits if your dictionary is a good one,” he told Kat Arney in an interview for the Naked Scientists podcast. “And so, I thought you know, to define what a mammal is, I’ll write a list of the traits we have hair, a unique type of cerebral cortex, three bones in our middle ears, a unique jaw joint… And I figured that each chapter of the book would describe fairly independently how each of these traits had evolved.” He deals with the reproductive system–mammals being the only group in which male reproductive organs are outside the body–lactation, chromosomes, brains, hair, bones, teeth, and other features of mammals, and how all these characteristics complement one another. “I thought at one point my big take-home on mammals was going to be about how the traits that define them are so wondrously adaptable. … Instead, what’s important is the combination of individual traits,” he writes. His study includes an examination of how this combination has made mammals the dominant animals on earth, while noting that there are fewer mammal species in the world than readers may expect–just 1,687, discounting bats and rodents.
Several critics found I, Mammal a valuable work of science that is, at the same time, accessible and entertaining. “Liam Drew really piles in the surprising facts (often surprising to him too) and draws us a wonderful picture of the various aspects of mammals that make them different from other animals,” remarked Brian Clegg on the Popular Science Web log. In Science Magazine‘s online edition, Michael A. Goldman called the book “a clear, conversational (sometimes to a fault), and engaging work that is especially good at explaining how evolutionary biology works.” According to a Publishers Weekly reviewer, Drew “combines detailed technical information with interesting natural-history tidbits” and “vividly conveys the excitement of scientific discovery,” writing “with wit and passion.”
A Kirkus Reviews contributor called I, Mammal “a solid and demanding account, one best read after some grounding in current evolutionary and biological theories.” BookPage online critic Becky Libourel Diamond thought Drew succeeded in “skillfully weaving scientific fact with beautiful prose and humor,” making his book “a compelling narrative for anyone who wants to discover more about what makes us tick.” Clegg, while praising I, Mammal generally, maintained that Drew spent too much time on details about his family, although the reviewer recognized that some readers would appreciate this aspect of the book. “Overall, this is a brilliant book, particularly if, like me, you know relatively little of biology or what makes mammals, erm, mammals,” he concluded. “It’s light enough to be enjoyable but detailed enough to satisfy the most fact-driven reader.” Goldman summed it up as “just the sort of book that can spark a love of nature and an appreciation for the ever-changing, eternally correcting march of science.” Booklist commentator Nancy Bent added: “Drew’s immersion makes one proud to be a mammal.”
BIOCRIT
PERIODICALS
Booklist, December 1, 2017, Nancy Bent, review of I, Mammal: The Story of What Makes Us Mammals, p. 22.
Kirkus Reviews, November 15, 2017, review of I, Mammal.
Publishers Weekly, November 6, 2017, review of I, Mammal, p. 73.
ONLINE
Bloomsbury Website, https://www.bloomsbury.com/ (March 21, 2018), brief biography.
BookPage Website, https://bookpage.com/ (January 16, 2018), Becky Libourel Diamond, review of I, Mammal.
Naked Scientists, https://www.thenakedscientists.com/ (October 8, 2017), Kat Arney, “What Makes a Mammal?” (broadcast transcript).
Popular Science Web log, http://popsciencebooks.blogspot.com/ (November 30, 2017), Brian Clegg, review of I, Mammal.
Science Magazine Website, http://blogs.sciencemag.org/ (January 8, 2018), Michael A. Goldman, review of I, Mammal.
Liam Drew is a writer and former neurobiologist. He writes about biology and biomedical research. His work has appeared in Nature, New Scientist, Slate and the Guardian. I, Mammal: The Story of What Makes us Mammals (Bloomsbury) is his first book. In his academic carrier he earned his PhD in sensory biology from University College London, then spent 12 years researching schizophrenia, pain and the birth of new neurons in the adult mammalian brain at Columbia University, New York and, again, at UCL. He lives in Kent, UK with his wife and two daughters.
Liam Drew
Media for author Liam Drew
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Liam Drew is a writer, former neurobiologist and mammal. He has a PhD in sensory biology from University College London, and spent twelve years researching the neural and genetic basis of schizophrenia, the biology of pain and the birth of new neurons in the adult mammalian brain at Columbia University, New York and at UCL. His writing has appeared in Nature, New Scientist, Slate and the Guardian. He is director of NeuWrite London, a London subsidiary of 'NeuWrite: a collaborative working group for scientists, writers, and those in between'. He lives in Kent with his wife and two daughters.
@liamjdrew
Writes: Popular Science
Author of : I, Mammal
Print Marked Items
Quoted in Sidelights: “combines detailed technical information with interesting natural-history tidbits” and “vividly conveys the excitement of scientific discovery,” writing “with wit and passion.”
I, Mammal: The Story of What Makes Us
Mammals
Publishers Weekly.
264.45 (Nov. 6, 2017): p73.
COPYRIGHT 2017 PWxyz, LLC
http://www.publishersweekly.com/
Full Text:
I, Mammal: The Story of What
Makes Us Mammals
Liam Drew. Sigma, $27 (336p) ISBN 978-14729-2289-2
With wit and passion, Drew, a freelance writer and former neurobiologist, explores what it means to be a
mammal by taking an evolutionary look at how and where mammals arose. He discusses such topics as the
origin of lactation, the nature of the placenta, the evolution of warm-bloodedness, and the characteristics of
the mammalian brain. He makes clear that none of these traits arose in isolation: "Individual traits can be
meaningfully defined and studied in isolation, but such an approach should never blind us to the fact that
every trait is a part of a greater whole." Throughout, Drew describes organismal evolution as a multifaceted
process that is difficult but not impossible to study. He presents the results of current research and offers
competing hypotheses to explain many of the developmental and behavioral patterns observed. Drew
vividly conveys the excitement of scientific discovery, reminding readers that there is much yet to be
uncovered. He combines detailed technical information with interesting natural-history tidbits, such as that
"marsupials have three vaginas--two for letting sperm in, and one for letting their joeys out." He also niftily
connects his personal experiences of fatherhood to the broader issue of animal reproduction. There's much
here to be savored by scientists and nonscientists alike. (Jan.)
Source Citation (MLA 8th
Edition)
"I, Mammal: The Story of What Makes Us Mammals." Publishers Weekly, 6 Nov. 2017, p. 73. General
OneFile, http://link.galegroup.com/apps/doc/A514056644/ITOF?
u=schlager&sid=ITOF&xid=49bdca75. Accessed 4 Mar. 2018.
Quoted in Sidelights: “a solid and demanding account, one best read after some grounding in current evolutionary and biological theories.”
Gale Document Number: GALE|A514056644
Drew, Liam: I, MAMMAL
Kirkus Reviews.
(Nov. 15, 2017):
COPYRIGHT 2017 Kirkus Media LLC
http://www.kirkusreviews.com/
Full Text:
Drew, Liam I, MAMMAL Bloomsbury Sigma (Adult Nonfiction) $27.00 1, 16 ISBN: 978-1-4729-2289-2
A tale of scrotality and other pressing mammalian concerns.
A neurobiologist by training, science writer Drew relates that some time ago, he got it in his head that
readers might enjoy "a lengthy discussion of the natural history of scrotums," and all that remained was to
find an editor who agreed with him. After some rejections, he did, first for a magazine and then for this
book, which indeed includes, among other things, a lengthy discussion of the natural history of scrotums--
perhaps too lengthy. The author explores other mammalian matters, of course, among them the fact that
there are not so many kinds of mammals in the world once one discounts bats and rodents: by his reckoning,
1,687 species. As Drew writes, "rats, mice, voles, squirrels, chipmunks, gerbils, guinea pigs and their kin
accout for just over 40 percent of all mammals." And, the subject being mammals, mammaries naturally
enter into the narrative, and the author connects their evolution to the triad of apocrine gland, sebaceous
gland, and hair follicle. Readers may be delighted to learn, finally, that the egg indeed preceded the chicken,
although "biologists are at a bit of a loss as to why the egg evolved." Drew's account is doggedly Darwinian,
allowing for modern interpretations of things like clades and radiative adaptations, and his argument often
proceeds from technical fine points. "Might the evolution of a key trait," he asks, "have given therapsids,
say, an edge over pelycosaurs? Did a uniquely mammalian character allow mammals to succeed
cynodonts?" The answer is an elusive yes and no, but the ability to entertain contending possibilities is
another thing that makes us human--i.e., mammalian with a few more folds of the cortex, descended
testicles, a constant body temperature, and such.
A solid and demanding account, one best read after some grounding in current evolutionary and biological
theories.
Source Citation (MLA 8th
Edition)
"Drew, Liam: I, MAMMAL." Kirkus Reviews, 15 Nov. 2017. General OneFile,
http://link.galegroup.com/apps/doc/A514267810/ITOF?u=schlager&sid=ITOF&xid=7716bfbe.
Accessed 4 Mar. 2018.
Quoted in Sidelights: “Drew’s immersion makes one proud to be a mammal.”
Gale Document Number: GALE|A514267810
I, Mammal: The Story of What Makes Us
Mammals
Nancy Bent
Booklist.
114.7 (Dec. 1, 2017): p22.
COPYRIGHT 2017 American Library Association
http://www.ala.org/ala/aboutala/offices/publishing/booklist_publications/booklist/booklist.cfm
Full Text:
* I, Mammal: The Story of What Makes Us Mammals.
By Liam Drew.
Jan. 2018. 336p. Bloomsbury/Sigma, $27(9781472922892). 599.
The birth of his daughter sent neurobiologist Drew an important message. For 20 years, he had studied
biology, and only with her arrival did he realize that he was biology. As thoughts of pregnancy and his new
child obsessed him, Drew perceived that everything he was preoccupied with was quintessentially
mammalian, and therefore, he takes the reader along on a quest to understand what makes us mammals.
Starting with an intriguing evaluation of the scrotum (mammals are the only group that keeps the male
reproductive organs outside the protection of the body), Drew looks at the evolution of various mammalian
traits. Platypuses demonstrate the early evolution of lactation as, despite being egg-laying, these
monotremes provide milk for their young. The rise of mammalian copulation is specifically due to the
evolution of the vagina. In his highly readable and anecdotal style, Drew explains the differences between
placental and marsupial mammals that go beyond the presence or lack of a pouch; the delicate balance the
placenta maintains between mother and fetus; the myriad forms of milk, the sole food of infant mammals;
the infant-rearing role of fathers (usually not much); and the role of teeth in mammalian evolution. Drew's
immersion makes one proud to be a mammal. --Nancy Bent
Source Citation (MLA 8th
Edition)
Bent, Nancy. "I, Mammal: The Story of What Makes Us Mammals." Booklist, 1 Dec. 2017, p. 22. General
OneFile, http://link.galegroup.com/apps/doc/A519036161/ITOF?
u=schlager&sid=ITOF&xid=b3e43741. Accessed 4 Mar. 2018.
Gale Document Number: GALE|A519036161
Quoted in Sidelights: “skillfully weaving scientific fact with beautiful prose and humor,” making his book “a compelling narrative for anyone who wants to discover more about what makes us tick.”
Web Exclusive – January 16, 2018
I, MAMMAL
What it means to be warmblooded
BookPage review by Becky Libourel Diamond
Chances are most of us don’t give much thought to what it means to be a mammal. In science class we learn that mammals are warmblooded and give birth to live young. But it is much more complicated than that, as writer and former neurobiologist Liam Drew explains in his fascinating debut, I, Mammal.
As a scientist, Drew had a good working knowledge of mammals and their evolution. But becoming a father changed his perspective. The natural human processes of pregnancy, childbirth and breastfeeding piqued his curiosity regarding the specific traits that make us mammals. As he notes, “For twenty years, I’d studied biology; finally, I understood that I was biology.”
Each chapter is devoted to a specific aspect of mammalian biology, such as X and Y chromosomes, the reproductive process and the calories we need to support our warmblooded lifestyle (up to 20 times more than our coldblooded cousins). He explains how mammals are divided into three groups: the monotremes, marsupials and placental animals. Some of the facts are mind-boggling: Placental animals (yes, that includes us) make up the overwhelming majority of the three types, with 5,080 species to be exact, 2,277 of which are rodents.
Although mammals share many commonalities, there are vast differences, too, demonstrating the delicate balance between survival and extinction. Drew explains these in detail, such as the painstaking, dangerous journey marsupial infants must take to reach their mother’s mammary glands. It is amazing just how long it took scientists to understand many mammalian functions and how many theories are still being debated. Drew discusses these various hypotheses, often pointing out those he feels carry the most weight.
Skillfully weaving scientific fact with beautiful prose and humor, I, Mammal is a compelling narrative for anyone who wants to discover more about what makes us tick.
Quoted in Sidelights: “Liam Drew really piles in the surprising facts (often surprising to him too) and draws us a wonderful picture of the various aspects of mammals that make them different from other animals,”
“Overall, this is a brilliant book, particularly if, like me, you know relatively little of biology or what makes mammals, erm, mammals,” he concluded. “It’s light enough to be enjoyable but detailed enough to satisfy the most fact-driven reader.”
November 30, 2017
It's rare that a straightforward biology book (with a fair amount of palaeontology thrown in) really grabs my attention, but this one did. Liam Drew really piles in the surprising facts (often surprising to him too) and draws us a wonderful picture of the various aspects of mammals that make them different from other animals.
More on this in a moment, but I ought to mention the introduction, as you have to get past it to get to the rest, and it might put you off. I'm not sure why many books have an introduction - they often just get in the way of the writing, and this one seemed to go on for ever. So bear with it before you get to the good stuff, starting with the strange puzzle of why some mammals have external testes.
It seems bizarre to have such an important thing for passing on the genes so precariously posed - and it's not that they have to be, as it's not the case with all mammals. Drew mixes his own attempts to think through this intriguing issue with the historical debates over it, leading up to the latest thinking.
This is the broad approach Drew tends to take in most of the chapters, whether we're looking at the jaw bone (apparently the most distinctive aspect of mammals), the senses, being warm blooded (but we're not allowed to call it that), hairiness or lactation. That last item had one of the most striking statistics amongst the 'Wow!' facts Drew gives us - that one species of whale when suckling young produces about a quarter of a tonne of milk a day.
Another delightful feature that recurs through the book is the duck billed platypus. After diving into this weird and wonderful creature in some detail early on, they keep cropping as their odd position on the mammalian family tree makes them an inevitable recurring reference point. And the more you read about the platypus, the more you love it.
Only two things were less than perfect. A couple of chapters fell into the Feynman Trap by spending too much time naming things and losing steam a little on the narrative, but these weren't too much of an issue. The other problem for me is a personal one. Drew uses his children and details of family life, particularly of the premature birth of his first child, far too much for me. I know some people (and publishers) love all these personal details, but I found it mildly nauseating - however, I'm sure that's just me.
Overall, this is a brilliant book, particularly if, like me, you know relatively little of biology or what makes mammals, erm, mammals. It's light enough to be enjoyable but detailed enough to satisfy the most fact-driven reader. Recommended.
Quoted in Sidelights: “a clear, conversational (sometimes to a fault), and engaging work that is especially good at explaining how evolutionary biology works.”
“just the sort of book that can spark a love of nature and an appreciation for the ever-changing, eternally correcting march of science.”
Books, Et Al.
Book and media reviews from the journal Science, edited by Valerie Thompson.
Valerie Thompson
Valerie Thompson, Editor
BOOK DEVELOPMENTAL BIOLOGY, EVOLUTIONARY BIOLOGY
A witty romp through evolution reveals a trove of curiosities in mammalian biology
By Michael A. Goldman
January 8, 2018
I, Mammal: The Story of What Makes Us Mammals
Liam Drew
Bloomsbury Sigma
2018
336 pp.
Purchase this item now
In today’s world of alternative facts and attenuating funding of research, scientists need to communicate with the public as we never have before. Joining the ranks of a burgeoning number of professional scientists turned professional writers, Liam Drew, a practicing neuroscientist for 12 years, has put down his microfuge tubes and taken up the charge. His first book, I, Mammal: The Story of What Makes Us Mammals, stands out as a clear, conversational (sometimes to a fault), and engaging work that is especially good at explaining how evolutionary biology works.
Drew was drawn to the topic of mammalogy through personal experience. In the book’s introduction, “My family and other mammals,” he describes witnessing his wife give birth, watching his newborn daughter suckling in the neonatal intensive care unit, and the painful encounter with an errant football that led him to question the wisdom of the external placement of the testes.
Beyond the descent of man’s gonads, Drew’s tour of Class Mammalia ranges into early mammalian evolution, sex determination, reproduction, lactation, parental investment, warm-bloodedness, and the complexity of the brain.
Drew is an enthusiastic advocate for the field of “evo-devo,” the enthralling combination of developmental and evolutionary biology. He is particularly captivated by August Weismann’s 19th-century conceptualization of “germ plasm” (the idea that heritable information is transmitted only by germ cells), writing that it should have been a “Copernicus moment” for biology. “[A]ppreciating the germline takes our everyday notions that we own our sperm or eggs and turns it back to front.”
In a cleverly titled chapter on sex determination (“Y, I’m male.”), Drew credits the American geneticist Nettie Stevens with the discovery of the X and Y chromosomes in 1906. Stevens’s work, as he describes, not only explained chromosomal sex determination but also provided incontrovertible evidence that the chromosomes played a role in hereditary traits. (The discovery of the genetic basis of male sex determination would take nearly another century.)
Drew’s narratives of the essential characters of mammals—and his discussion of the evolution of marsupials and monotremes in particular—are quite engaging and entertaining. “Famously,” he writes “the first academic description of a platypus questions whether it was a hoax … an outright assault on the neat categories Linnaeus had spent years establishing.”
Drew is sensitive to the tension that the past half-century has seen between the molecular/cellular and the whole-organism approaches to taxonomy. He ultimately comes down in favor of molecular approaches, observing that “Nothing about limbs and genitalia makes their construction especially useful for inferring their evolutionary history.” However, in a nod to the value of morphology, he does acknowledge that “appreciating their development can help increase evolutionary understanding.”
Some fascinating aspects of mammalian genetics were decidedly missing from I, Mammal, including the silencing of one of the two X chromosomes that occurs in most cells of most female mammals (X-chromosome inactivation), the expression of only one of the two copies of a substantial number of genes inherited (genomic imprinting), and the phenomenon of epigenetics.
As a developmental biologist, I would also have had trouble telling the story of mammals without mention of reproductive cloning and Dolly the sheep. However, selected references for each chapter, as well as an index, allow the reader to follow up on interesting topics.
KEVIN SCHAFER/ALAMY STOCK PHOTO
The author’s encounter with an errant football led him to question the wisdom of external testes, as seen here on a stump-tailed macaque.
Writes Drew, near the end of the book: “I thought at one point my big take-home on mammals was going to be about how the traits that define them are so wondrously adaptable. … Instead, what’s important is the combination of individual traits.” It’s hard to argue with his conclusion, but I think the emphasis on adaptability is misplaced; it’s an obvious consequence of natural selection. The same, after all, could have been written about almost any other group of organisms as well.
Ultimately, however, I, Mammal is just the sort of book that can spark a love of nature and an appreciation for the ever-changing, eternally correcting march of science. It brought this reviewer back to a time spent wondering about the birds chirping outside and the creatures lurking in tide pools, rather than dealing with the more tedious tasks required of a practicing biologist.
The book is not a plea to preserve the enormous diversity of mammals, although it does bring up curiosities of mammalian biology that will no doubt delight and surprise even practicing scientists. I hope it will give every reader a taste for more.
In the end, I, Mammal serves more as a reminder of what we owe to the cataclysmic extinctions of the past. The idea that our species is likely to have only a short tenure on Earth is one that we should always keep in mind.
About the author
The reviewer is at the Department of Biology, San Francisco State University, San Francisco, CA 94132, USA.
Quoted in Sidelights: “You look it up in the dictionary and it says a mammal is a warm-blooded vertebrate with hair and mammary glands, maybe a few other traits if your dictionary is a good one,” he told Kat Arney in an interview for the Naked Scientists podcast. “And so, I thought you know, to define what a mammal is, I’ll write a list of the traits we have hair, a unique type of cerebral cortex, three bones in our middle ears, a unique jaw joint… And I figured that each chapter of the book would describe fairly independently how each of these traits had evolved.”
What makes a mammal?
08 October 2017
Interview with
Liam Drew
Part of the show Evolution's luxury item
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From tiny shrews to enormous blue whales, polecats to polar bears, mammals have expanded across the planet to fill a wide range of environmental niches from the frozen Arctic to the fiery desert. But what actually makes a mammal a mammal? That’s a question that bothered neuroscientist-turned science writer Liam Drew when he accidentally took a very painful football to the groin while playing goalkeeper - as only mammals keep their vital reproductive organs dangling about on the outside.
Luckily this didn’t stop him becoming a father, and during that process he became fascinated by the underlying biology - a live baby growing in the womb, fed through a placenta, and then nourished on milk produced by the mammary glands from which mammals get their name. You might think of other traits, such as having fur - but if all it takes is hair and milk, then is a coconut a mammal? To get to the bottom of this mammalian mystery, Kat Arney caught up with Liam at the Wellcome Collection in central London for a chat about his new book on this very subject - I, Mammal.
Liam - You look it up in the dictionary and it says a mammal is a warm-blooded vertebrate with hair and mammary glands, maybe a few other traits if your dictionary is a good one. And so, I thought you know, to define what a mammal is, I’ll write a list of the traits we have hair, a unique type of cerebral cortex, three bones in our middle ears, a unique jaw joint... And I figured that each chapter of the book would describe fairly independently how each of these traits had evolved. And so, it was great fun, looking at how milk had evolved or…
Kat - Boobs and willies, you know.
Liam - Yeah, well I guess I was inspired by reproductive biology, so it did start in the bathing suit area and I’d like to try and move beyond that...
Kat - This is a scientific book obviously!
Liam - Yes, exactly. Well, I did end up trying to arrange the book, having started with the scrotum and saying, “Look! Life begins when sperm are made there and obviously, when eggs are made in the ovaries.” And then I tried to trace the arc of a mammalian life. But to go back to your question, I have this list of traits and this was very 18th century really. You know, the actual classification of mammals can be traced to Linnaeus in the mid-18th century, 1758.
Kat - He did love a bit of classification.
Liam - He did love a bit of classification! And so, it’s in the same book that he coined the term Homo sapiens, that he coined the term mammals. But anyway, next to these 200 primarily European mammals, he had a list of the traits they had and that’s how they did it then. And of course, Darwinian Theory a hundred years later really turned everything on its head. But I think what was important in writing the book, in trying to come up with what a mammal was, was that the chapters weren’t independent at all.
When I was writing about the scrotum, it wasn’t like this made sperm production better. It was like, this is a necessary adaptation to either mammals becoming more warm-blooded or essentially because they started galloping in a certain way which made the abdomen susceptible to these waves of pressure. So we have these two traits of the animal which changed its characteristic.
And then once you went to mammary glands, the sort of main theories on why milk evolved was that before it was a food stuff, it was a useful secretion to either keep eggs moist or to stop from dehydrating, or that the secretion contained components of the innate immune system which killed microorganisms which would have proliferated more on eggs as mammals became warm blooded. So you have this warm-blooded animal laying warmer eggs that needed to be protected either from dehydration or from microorganisms. And so again milk was tied to the warm bloodedness.
There was this fantastic essay written in 1977 on why lactation was important - it was actually published in a month when I was actually being breastfed, which I kind of liked that connection - by Caroline Pond at Oxford University and she listed how as soon as milk could have evolved it changed the landscape again for the possibilities of the animals that possessed it. So suddenly, by the newborns being fed milk, they didn’t have to hunt their own food. And so, they didn’t need such good teeth and so they could grow to a sort of fairly adult size and have an adult jaw and only grow their teeth in an adult jaw.
Mammals have one set of milk teeth and an adult dentition. One of the really defining things of mammals is how sophisticated their teeth are. And one of the things about them is that they interlock perfectly between upper and lower jaws which allows us to chew food very efficiently which helps power this warm blooded metabolism of ours. So again, it was just sort of link upon link. So as soon as I got to the warm-blooded chapter, it was like, “Hey, remember. All these other stuff was spoken about.”
Kat - You can't forget any of it. It seems like being a mammal is absolutely not this like 18th century tick list of, if you’ve got all seven of these, you're definitely a mammal. It’s more like kind of, “do you fit into this weird Venn diagram?” because there must be exceptions. There must be mammals that are weirdly exceptional.
Liam - So, as soon as you say a mammal is an animal with hair, you have a problem with dolphins – they have hair in utero and a few hairs around their mouths when they're first born. But then they have…
Kat - Yeah, like a tiny mustache.
Liam - Yes, apparently useful for finding the mother’s teat. But the dolphin has lost that hair. It’s lost this definition or trait, but it’s still defined by its high energy level lifestyle and all these other traits which allow it to function.
Kat - When we’re talking about Linnaeus, we’re talking about the idea of what is a mammal, Linnaeus and the taxonomists, they love to classify things and say, “Well, it’s got this structure and that form, and so, it must be this kind of animal.” But now, we have genetics. What is genetics telling us about what it is to be a mammal and where we came from?
Liam - When people starting doing taxonomy after Darwin, which was based upon shared history and inter-relatedness, the groups look quite similar with what Linnaeus had come up with because one sort of assumed that a shared physical characteristic meant you are very closely related.
Kat - If you look like a mouse, you're probably some kind of like rodenty mousey thing.
Liam - Yeah, precisely. For a century after Darwin, people were doing taxonomy on morphological basis. And then in the late 1950’s and early ‘60s, this idea of using – it was actually Francis Crick who, in a 1957 lecture said we can start using protein sequences or DNA sequences to trace relatedness. Instead of looking at morphological features, look at protein or DNA sequences of different species and and then further interrelatedness from that.
And it was a wonderful idea. Linus Pauling did this with primate hemoglobin and of course, DNA sequencing was incredibly arduous and hardwork for a long time. Some of the morphologists didn’t really trust this and you can kind of imagine that, right? People who know animals incredibly well and infer everything from all their features, suddenly, guys with test tubes of DNA are like, “Hold on buddy. I've got this covered.” People who’ve never even held an animal could use DNA to infer inter-relatedness.
Kat - It must be a bit like having a paternity test going. “No. That’s definitely my kid.” And it’s like, “DNA says no. I'm afraid that is not a rodent.”
Liam - Exactly. And so, this back and forth went on and on, and in the early ‘90s, some molecular biologists said, “Actually, we don’t think a guinea pig is a rodent” and everyone just sort of dismissed it as very silly. And then suddenly, in 1997, this group in California led by Mark Springer suddenly published this paper entitled, “African Mammals Shake the Mammalian Family Tree.” They basically showed on really robust genetic evidence – they’d really assembled more genetic evidence than anyone had ever previously done – and they suggested that actually, there was a group of African mammals which were more closely related to one another than any other types of mammals.
Kat - So, when people started to discover that DNA was telling us different stories about mammalian history than the fossils, and then the actual physical shapes of mammals, should this change the way that we think about what it means to be a mammal? Is there a genetic definition of what it is to be a mammal?
Liam - The genetics data is now overwhelming in this classification of four groups. One of the really interesting things that it did is that it really tied mammalian evolution to geography. And so, there was the original African group and then the data showed very convincingly that the South American mammals, the sloths, the ant eaters, and armadillos were very closely related forming another group. And there was a third group which could be subdivided in two which evolved on Eurasia. So it actually tied really nicely together the genetic story and the geography of the world.
Kat - I love how in the book you describe mammals as being almost like luxury items in evolutionary history.
Liam - Yeah and I had a moment - that was actually in Darwin’s garden, I think - I was just wandering around there and it’s a beautiful house and it was a weird moment of thinking, ‘there's a lot of plants there’. I was all alone in the woodland behind his house where he used to walk. I'm just thinking, “Look at all these wood and all these plants.”
I mean, it’s absurd – the amount of energy we use. We’re not energy efficient. 95 per cent of our energy consumption goes on just maintaining our temperatures, maintaining our physiology. Together, we are a luxury. You couldn’t have a world made of mammals. We’re reliant on just eating and consuming all the time.
Kat - We are biology’s luxury.
Liam - Yeah, maybe!
Kat - Liam’s book, I, Mammal, is published by Bloomsbury Sigma on the 2nd November, and is available from all good retailers/