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A groundbreaking study reveals that human brains are filled with a staggering amount of plastic, challenging our understanding of the human experience. From the biology of sex to the impact of microplastics on our minds, this conversation explores the fascinating and often overlooked world beyond the male-female binary.
The Biology of Sex and Plastic in the Brain: A Discussion
A January executive order by President Donald Trump defines individuals as female if they produce the ‘large’ reproductive cell (the egg) and male if they produce the ‘small’ one (the sperm). However, human sexes do not fit neatly into a male-female binary due to factors such as genetics and hormones.
Humans are typically categorized into two biological sexes: male and female.
Male sex is characterized by the presence of XY chromosomes, while female sex has XX chromosomes.
However, some individuals may have variations in their chromosomal makeup, such as XXY or XYY.
Additionally, there are intersex conditions where an individual's reproductive anatomy doesn't fit typical definitions of male or female.
According to a 2020 report by the United Nations, about 1.7% of births globally have some form of sex variation.
Understanding Reproductive Cells
Reproductive cells change throughout development, making a sex definition based on size tricky. In developing embryos, primordial germ cells (PGCs) form before ovaries and testes do. These cells are huge and start off roughly the same size, regardless of the type of gonad an embryo forms.
After gonads form, meiosis further complicates things. In human females, meiosis produces one large egg cell and two small infertile cells called polar bodies. In males, a PGC replicates its genome several times without splitting into product cells, producing a huge cell with multiple nuclei that then jettisons tiny sperm cells.
Plastic Shards in the Brain
A study of nearly 100 human brain samples shows that micro- and nanoplastics (MNP) have increased substantially over time. The median concentration of MNPs increased by about 50 percent from 2016 to 2024, with an estimated 4,917 micrograms of plastic present in an entire human brain – roughly three bottle caps’ worth.
Microplastics, smaller than 5 millimeters, and nanoplastics, less than 1 micrometer in size, have become a pressing environmental issue.
These tiny plastics are released from various sources, including cosmetics, clothing, and plastic bags.
They contaminate waterways, oceans, and even the food chain.
Research suggests that microplastics can be ingested by humans through drinking water and food, potentially leading to health problems.
The World Health Organization estimates that 80% of tap water worldwide contains microplastics.
Brain Variability and the Study’s Limitations
The study measured MNPs only in samples from the brain’s frontal cortex. Brains vary in weight, as do bottle caps, making it unclear whether plastic loads differ depending on brain region. Additionally, the study did not account for potential variations due to other factors such as lifestyle or environmental exposure.
Appreciation for Scientific Coverage
Reader Diana Lutz greatly enjoyed the April issue’s three features on nuclear weapon testing, biological sex, and the carbon credit market. She praised the articles for covering important topics rarely examined at depth, resolving lingering questions she had about each topic.
- sciencenews.org | Readers discuss the biology of sex, plastic in the brain and more
