New book demystifies human sex via highly memorable non-human comparisons

It’s a challenge to write something original on a topic that’s as old as time, but the subject of sex is arguably never boring. Facuty of Science Professor Alexander Mills, associate dean, students, proves this point in spades. He has written an engaging and intellectually challenging new textbook, Biology of Sex, published by the University of Toronto Press (2018).

In this new book, Mills approaches the topic of sex and reproduction in a wholly original way by presenting intriguing comparisons between human sex and the many variations in sexual systems among non-human organisms. “By comparing the characteristics and patterns of a diversity of species, our knowledge of all life, including humans, is enriched,” he explains.

It’s not for the faint of heart. The author describes quite a few non-human species that maim, coerce, kill and eat their partners during the mating process, for example. Indeed, this publication is chock-a-block with highly memorable biological truths.

Alexander Mills and the cover of his book, published by U of T Press. Image reproduced with permission

In writing this book, Mills sought to demystify so-called black box topics – voids in most people’s understanding of sex and the “facts of life.” This publication reflects Mills’ keen interest in aiding scientific literacy and, more specifically, improving the methods of teaching post-secondary biology.

“It’s well accepted that graduates will fare better having achieved some real scientific literacy.” – Alexander Mills

Comprehensive book covers vast territory

Mills tackles this very large topic systematically over 400+ pages, considering genetic, physiological and evolutionary principles. He opens with sexual reproduction; asexual reproduction, as in the case of bacteria; and non-sexual reproduction in unicellular and multicellular organisms. He then moves on to sex and inheritance, which profiles DNA and chromosomes.

Chapter 4, on sex and evolution, is very interesting as it discusses the principles of natural selection and the role of sex in the creation of species. Chapter 5 continues the discussion on sexual selection, a subcategory of natural selection.

Male brown marsupial mice seek copulation so rigorously that it kills them

The book also profiles mating systems by breaking the topic down into monogamy and several types of polygamy, including polyandry, a form of polygamy where a female takes two or more male partners at a time. Mills also covers homosexuality. He states that homosexuality and associated behaviours, including same-sex courtships and pair-bonding behaviours, exist in hundreds of species, including mammals, birds, reptiles and insects. The biology of sexual conflict – before, during and after mating, and during parenting – is also covered.

Some content will be controversial

The book tackles many timely issues, some of which will be controversial.

Assigned sex, transgender and gender dysphoria, which occurs when sex assignment based on genital inspection does not align with the individual’s developing identity, are discussed. Mills explains that in the natural world there are individuals who are not clearly male or female, and many organisms are gender neutral. “However, the binary, male-female model runs very deep in biology,” he writes.

In Part 8, the author notes that environmental sex determination can override genetic sex determination in nature – as is the case for many developing reptiles. He also considers cases where mothers can use temperature to select their offspring’s sex and reflects on social systems of sex determination. Sex allocation is adaptive when having offspring of a particular sex is advantageous, he reports.

Mills also considers anomalies in sex chromosomes, genetic mutations, intersex conditions and rare cases where children who appear to be girls develop into men at puberty.

A female praying mantis kills and eats its partner during and after copulation

Many facts will stay with readers

Some biological truths will, doubtlessly, linger in the minds of readers – a clear indication that the author has succeeded in his goal to engage readers. The most memorable facts may include the following:

  • Male brown marsupial mice are so single-minded during mating season that they allow their internal systems to break down, resulting in an early death.
  • A praying mantis cannibalizes her male partner during and following mating.
  • Sex change is common in clownfish (Finding Nemo), and cleaner wrasses (another reef fish) can change their sex if the need arises. For example, if two males are placed together, the smaller one will revert into a female.
  • Male scorpion flies capture prey, which they use to “negotiate” with the female for mating privileges.
  • Hermaphroditic flatworms engage in penis fencing, where each seeks to win by inseminating the other.
  • Parasitic castration occurs when a host’s reproductive system is taken over, as in the case of the green shore crab.
  • When a Hanuman langur (monkey) colony is taken over, the conquering males kill the existing babies, then mate with the females to start a new breeding cycle.
  • Studies of songbirds show that extra-pair mating is usually done covertly – that is, in a secret location.
Hermaphroditic flatworms penis fence and seek to win by inseminating the other. Wikipedia, photo credit: Nico Michiels

Author credits York for its interdisciplinary approach

In the book, Mills credits York University’s exceptional interdisciplinary strength for providing an optimal environment for students and a supportive one in which he could create this book.

“York University embraces the tradition of interdisciplinary education. This educates students in a manner that prepares them for life.” – Alexander Mills

“York embraces the tradition of interdisciplinary education, which means that a component of the student’s degree includes enrichment in areas outside the major,” Mills says. “This educates students in a manner that prepares them for life. It’s well accepted that graduates will fare better having achieved some real scientific literacy,” he adds.

To learn more about this book, visit the U of T Press website. For more information on Mills, see his faculty profile page.

To learn more about Research and Innovation at York, follow us at @YUResearch, watch the York Research Impact Story and see the snapshot infographic.

By Megan Mueller, senior manager, research communications, Office of the Vice-President Research and Innovation, York University,