Sharks are among the slowest-reproducing and latest-maturing of all vertebrates, and their pregnancies are long. Nurse sharks take a long time to grow up: males take about 10 to 15 years to mature and females about 15 to 20 years, so a nurse shark is at least ten years old before it can breed. Blue sharks mature considerably earlier, at about five years old, and until they reach that age the juveniles typically stay in pupping areas. Because sharks grow slowly and have few young, fishing can wipe out a population faster than it recovers.

White sharks grow slowly, and as of November 2026 males are estimated to mature at about 26 years and females at about 33, although some estimates for females say at least 30. Great white mothers give birth to live pups, not eggs, after a pregnancy thought to last a year or more, and a baby white shark is already about 4 feet long when it is born.

Litters and pregnancies differ from one kind of shark to another, and so do the ways pups develop before birth. Some sharks lay eggs in a tough egg case, where the embryo feeds on a yolk sac until it hatches. Other sharks give birth to live young that, before birth, feed on unfertilized eggs inside the mother, a habit called oophagy. Lemon sharks give birth to live pups after a pregnancy of about a year (10 to 12 months), in litters of fewer than 20 pups (4 to 19 by one count, 4 to 17 by another). Tiger shark litters are large for a shark, up to about 80 pups, but the young take a long time to develop: the pregnancy lasts a little over a year (16 months by one count). Blue shark pregnancy lasts 9 to 12 months, and litters usually run about 15 to 50 pups.

Scientists can estimate a shark's age by counting growth bands, like rings, in its backbone. For shortfin mako sharks, the age estimate depends on whether the vertebrae add one growth band pair a year or two. Some studies assumed two, others one, and recent work found one a year. Scientists tested carbon-14 left by nuclear-bomb testing (bomb radiocarbon) in the growth bands of whale shark backbones. It showed the sharks add one band every year, so counting the bands gives the shark's age. Researchers using bomb radiocarbon to check whale shark growth bands found one shark that was 50 years old when it died, which as of November 2026 is the oldest age seen for the species.

The same marker was used to age white sharks. Scientists used the radiocarbon that nuclear-bomb tests of the 1950s and 1960s left in the ocean, and one male was about 73 years old, far older than earlier estimates. As of November 2026, white sharks are thought to live from about 30 to more than 70 years. Greenland sharks, by contrast, grow very slowly, roughly 1 cm a year or less, which hinted that they live far longer than other vertebrates. Their age could not be read from growth bands, because their soft vertebrae have no growth bands, so the age was worked out by radiocarbon dating the center of the eye lens. As of November 2026, Greenland sharks may live for centuries: one study put the age of a large female at about 392 years, give or take 120. Greenland sharks are thought to reach adulthood only at around 150 years old, as of November 2026.

Teeth are the part of a shark most often found as fossils. Sharks have no bones, and their skeleton is made of cartilage. Complete fossil sharks are rare because cartilage is softer than bone, so scientists mostly find teeth. Helicoprion, a fish famous for a spiral of teeth, is known mostly from those tooth spirals, because almost none of the rest of its body was fossilized, and CT scans of a Helicoprion fossil showed that its spiral of teeth filled the whole lower jaw. Megalodon, one of the largest sharks that ever lived, is extinct and is known mostly from its teeth as well; no reliable megalodon fossil is younger than about 3.6 million years old, so it probably went extinct then.

The slow lives of single sharks sit inside a far longer story. As of November 2026, sharks have lived in the sea for more than 400 million years, long before the first trees about 385 million years ago. Doliodus problematicus, an early shark, lived about 400 million years ago in the Devonian Period, long before the dinosaurs existed. Modern kinds of sharks first evolved in the Jurassic Period, when giant dinosaurs lived, and sharks have changed very little in shape over millions of years.

Words to know

• radiocarbon: carbon-14 dating signal
• vertebrae: backbone pieces
• juveniles: young ones
• cartilage: bendy skeleton stuff
• Helicoprion: spiral-tooth fish