Thread by @HeatherEHeying

Ignorance, arrogance, and the wielding of credentials to shut down discourse: a triple threat.

When these three characteristics show up in one place, I feel a responsibility to at least slow the spread of misinformation. Here we go. [thread 1/26]

We are all ignorant of some things. Ignorance should be forgiven. 2/

Add arrogance and you have a problem brewing: an undeservedly confident tone that spews garbage will be confusing to some people, people who do not deserve to be confused by the ignorant, arrogant person in their feed. 3/

Add the wielding of credentials to shut dissent down—an appeal to authority that reveals how little such authorities deserve any power or respect at all—and it seems incumbent to step in. Now said person is actively getting in the way of inquiry and the discovery of truth. 4/

We’ve been here before, will likely be here again. Here’s a recent example of an ignorant, arrogant, credentialed dude thinking he had schooled me, when actually he just revealed his own inability to think carefully. 5/

https://twitter.com/HeatherEHeying/status/1377805849888923650?s=20

And now we have this. This guy is mouthing off about what sex is and is not, while trumpeting his PhD in biology. 6/

https://twitter.com/DeltaBCDad/status/1381291839165136896?s=20

Here is what binary means. I’ll say it loud for those of you who apparently slept through your entire graduate and undergraduate curriculum.

BINARY MEANS TWO STATES

Therefore starting out male and becoming female is a reference to…a binary. Male and female. Two states. 7/

This guy doubles down on his own confusion. And earlier, he makes oblique reference to reaction norms (in which diff environments can produce a range of phenotypes even when the genotype is identical), as if it’s relevant to his argument. (It’s not.) 8/

https://twitter.com/DeltaBCDad/status/1381336465800454144?s=20

Yes yes yes there are developmental errors. And intersex is real (also a developmental error, sometimes a genetic one). And ffs do you really think nobody knows that at this point?

Also, by the way, rare errors do not mean the entire system is misunderstood. 9/

So that’s one point: hermaphroditism does not disprove the sex binary. Hermaphroditism is in fact the state of having both sexes at once (simultaneous hermaphrodites) or moving between the two (sequential hermaphrodites).

Note “both”. And “two”. Two states. Binary. 10/

The errors here go on and on, but I’ll take on one more: his invocation of how sex is determined in sea turtles. He’s right about the temperature of the sand that eggs are laid in determining the sex of the hatchlings. It’s not clear to me that he’s right about much else. 11/

I’m going to cram a lot in here, which I don’t like to do, because it takes time & consideration to fully incorporate all this into your model of how evolution works, & how it has transpired on Earth. I used to give 3hr, interactive lectures on this stuff. That was better. 12/

In one of the lectures I used to give to my *undergraduates*, after we discussed the evolution of sex, I showed this slide—animated such that the figure to the right provides the answer to the question, “why anisogamy”? 13/

In adjacent lectures, I talked about conditions like haplodiploidy (as in ants bees and wasps, in which females are diploid—like humans—but males are haploid, having only half the genome), and parthenogenesis (broadly: asexual reproduction, be it obligate or facultative). 14/

Note that nobody from the “but we’re all evolved so anything could happen” camp are imagining that we could also become haplodiploid or parthenogenetic. Nope. 15/

Phylogenetic constraint—the fact of so much functional having to be undone in order to get to a different state, such that we vertebrates will never have, for instance, the more efficient eye of cephalopods (e.g. octopus)—does what it says: it constrains us. 16/

How is your sex determined?

Birds and mammals have Genetic Sex Determination (as do some other clades). It looks three different ways in these two clades: 17/

Basal mammals (echidnas and duck-billed platypus) have 9 or 10 sex chromosomes. It’s very weird. As are these organisms generally (to our modern eyes). Scientists are still actively trying to figure this system out. 18/
nature.com/articles/s4158…

Second, birds have one pair of sex chromosomes, but unlike in (most) mammals, females are heterogametic (ZW), males are homogametic (ZZ). (This is also the system that many snakes, and butterflies and moths, have.) 19/

Finally, most mammals (the metatherians—marsupials—and eutherians—placentals, that’s us) also have one pair of sex chromosomes, in the arrangement familiar to us: females are homogametic (XX) and males are heterogametic (XY). 20/

By comparison, lots of other species, including sea turtles, have Environmental Sex Determination. Specifically, sex is often determined by the temperature of the egg at a critical period during development. 21/

For instance:
tortoises: cool temp -> male, warm temp -> female
many lizards: cool temp -> female, warm temp -> male
crocodiles: warm and cool temps -> female, intermediate temp -> male [22/]

So what? Why do we care?

Well, we literally have NO EXAMPLES of individuals in a species with Genetic Sex Determination (GSD) actually changing sex. Functional sequential hermaphroditism, in which a male turns into a female, or vice versa, doesn't occur in species with GSD. 23/

The fact that even graduate programs in the sciences are failing to teach their graduates basic logic and comprehension is devastating, but not unexpected. Nearly every single one of my undergrad students would have been able to find flaws in this guy’s thinking. 24/

We worked, in my classrooms (and labs and fields) to lose our ignorance, but become as aware as possible of what of it remained. We tried to minimize arrogance. And my students didn’t have credentials to hide behind, but they knew and saw that I never silenced them with mine. 25/

Using a scientific credential to bully those who don’t have one, and to promote ignorant and wrong things, is anti-scientific, foolish and wrong. Y’all wonder why distrust of science and scientists is high now? Look no farther. You’re creating the problem. /end