Thread by @Anthrofuentes

There is a lot of talk about gametes (sex cells, ova (egg) and sperm) as the defining factor in sex biology and the essenceof females or males. A 🧵

This is based on Anisogamy, the production of different sized gametes (the main form of gamete production across animals). The size difference became the focus of many hypotheses about large and small gamete producer differences

Biologists usually refer to small gamete producers as male and large gamete producers as female.

Current hypotheses about anisogamy derive from Darwin’s assumptions about the differences in males and females and something called Bateman’s principles. These are popular hypothesis in biology and are now being used for legal decrees.

The basic idea behind them is that sperm are cheap, and eggs are expensive. This “cost” difference sets up different evolutionary stories, and lives, one pattern for males and another females. But reality is far from this simple or clear.

It turns out that both Darwin and Bateman made assumptions that don’t always hold up across species. Plus, there is much biological research that challenges the assertion that diffs in gamete size (anisogamy) means the same thing, or has the same impact, across all animals.

So, at least some awareness of these important discussions is necessary before simply accepting that anisogamy, and gametes, tell you everything you need to know about sex for a species, and the individuals in it. Esp. if you are making laws based on this assumption.

Here is the Wikipedia page for Bateman’s principle and it has a fairly balanced take w/good citations en.wikipedia.org/wiki/Bateman%2…

And here is a great overview of some of the errors (in the midst of many successes) Darwin made when envisioning females… degruyter.com/document/doi/1…

Note: there are many links to article/books in this🧵. But I don’t link to any individuals here…you have their names from the articles, and please if interested in their work do find them and check out their own threads/posts/other articles.

Let’s start with the basic “gametes as the defining factor in biology and the essence of females or males” perspective…this recent essay lays out the view very well (and its tie to the current legal arguments of the Trump admin): bostonglobe.com/2025/02/20/opi…

But, not all is as clear as some might argue in regards to sexual selection, Bateman’s principle and mating dynamics…it seems having sperm or egg does not always result in the same thing. Plus, sex is messy. Here are a bunch of reads that illustrate that…

A recent very general overview: Biological sex is not as simple as male or female sciencenews.org/article/biolog…

“ to uncover the causes of the immense natural variation in sexual selection and sex roles, the number and sizes of gametes are important but not sufficient”
academic.oup.com/evlett/article…

“We propose that ecological factors, life-history and demography have more substantial impacts on contemporary sex roles than the differences of gametic investments between the sexes.” nature.com/articles/s4159…

“At best, Bateman's principles should be considered hypotheses and approached with great care” pnas.org/doi/10.1073/pn…

“AJ Bateman's laboratory data are inconsistent with “Bateman's Principles.”” pmc.ncbi.nlm.nih.gov/articles/PMC75…

“We argue that human mating strategies are unlikely to conform to a single universal pattern.”
pmc.ncbi.nlm.nih.gov/articles/PMC30…

“using Bateman gradients to measure the potential for sexual selection may be misleading for some mating systems and life histories” academic.oup.com/beheco/article…

Plus a few excellent books on the subject:

“From lemurs to spiders, this gleeful exploration of female sexuality in the animal world overturns a host of outdated assumptions” amazon.com/Bitch-Female-S…

“when it comes to evolution—diversity wins” harpercollins.com/products/the-s…

“Our genomes are not blueprints, algorithms, or recipes for the physical representation of our individual sexual essences or fates.” press.uchicago.edu/ucp/books/book…

The assumption that gametes are the one true key to what makes a male or female evolutionarily, ecologically, behaviorally or individually are tenuous at best and not correct in many cases. There is no one universal “essence” to male or female.

Bottom line: Anisogamy doe matter and is a relevant aspect of organismal biology, but its impacts are neither universal or uniform across species and lineages.

"does" matter

For humans, this means that that a sperm is not “man” and an egg is not “woman.” But that is a whole other thread, or better yet a book… press.princeton.edu/books/hardcove…