Biodiversity and the meaning of sex

In the 1990s, vultures in India began dying after eating the carcasses of livestock that had been treated with a painkiller called diclofenac. With few vultures left to clean up carcasses, the number of feral dogs exploded. Because those dogs can carry rabies, human rabies deaths rose too: the loss of one kind of animal rippled all the way to human health.

What biodiversity is and why it matters

The variety of species living in an area, together with the genetic variety within those species, is the area’s biodiversity. Biodiversity isn’t only about wild species in remote places. It’s also tied to human well-being, prosperity, and people’s connections to nature.

Ecosystems, the communities of organisms in an area together with their physical environment, tend to function better when biodiversity is higher. Diverse communities also hold up better against disease and have a better chance of coming through disasters. For people, the payoffs fall into three main areas:

Each species that disappears narrows future options. It leaves fewer wild relatives to breed new crops from (every crop began as a wild plant reshaped by artificial selection) and fewer places to look for new medicines.

Protecting biodiversity

Biodiversity has been declining for decades, but people can slow the loss and perhaps even reverse it. Conservation efforts over the past several decades have already made a real difference, and understanding what threatens species helps people prepare for new conservation challenges.

Hundreds of thousands of protected areas, such as national parks, wildlife refuges, and marine reserves, give wildlife places to live and help limit deforestation. Protecting habitats isn’t enough on its own, though; restoring biodiversity will take several kinds of human action working together.

What biologists mean by sex

In biology, the words female and male describe sex, which is based on physical characteristics. They don’t describe gender. Gender refers to characteristics of women and men that are socially constructed, such as the roles, norms, and expectations a society attaches to each.

In humans, sex involves several kinds of characteristics:

• At birth, sex is usually assigned by looking at the external reproductive body parts: typically a vulva and vagina in females, and a penis and scrotum in males. When these external structures don’t match either of the two common patterns, they are called intersex structures.
• Sex is also linked to internal reproductive structures (such as ovaries, testes, fallopian tubes, and seminal vesicles), to levels of hormones (chemical messengers such as estrogen and testosterone), and to secondary sex characteristics, body features that develop once puberty begins. All of these vary widely. Intersex people have sex characteristics that don’t fit the two most common patterns.
• Sex determines the type of gamete, or reproductive cell, that an individual can potentially produce. Fertile females produce eggs (oocytes), and fertile males produce sperm.
• Chromosomes are the structures that carry a cell’s DNA, and X and Y are the sex chromosomes. Females are usually XX and males usually XY, but other combinations occur in humans, including XXX, XXY, and a single X.

Sex is not strictly binary. Anatomy, hormone levels, gametes, and chromosomes may be typical of females or of males, yet humans and other animals offer many examples that don’t fit a simple two-category scheme.

Check yourselfTwo forests hold the same number of species. In one, the members of each species are genetically very similar; in the other, they vary a lot. Which forest has greater biodiversity?

The forest with more genetic variation. Biodiversity includes both the variety of species in an area and the genetic diversity within those species.

Check yourselfHow does the biological meaning of “female” and “male” differ from gender?

Female and male refer to sex, which is based on physical characteristics such as reproductive structures, hormone levels, the type of gamete an individual can produce, and sex chromosomes. Gender refers to socially constructed characteristics, such as roles, norms, and expectations.