AND IT'S JUST A MATTER OF WHOSE IS THE BEST ONE:

Evolution's Bad Girl: Ardi shakes up the fossil record (Bruce Bower, January 16th, 2010, Science News)

Disputes over Ardi’s evolutionary relationships to living and extinct apes seem cordial compared with debate over her sexual relationships and their implications for ancient hominid social life.

This fracas goes back to 1981, when Lovejoy published a paper in Science about the sex life of what was, at that time, the earliest known hominid species,

Australopithecus afarensis. The most famous member of that species is Lucy, a 3.2-million-year-old partial female skeleton found at another Ethiopian site in 1974. Lovejoy proposed that Lucy’s kind possessed traits consistent with what amounted to a sexual revolution in the ape world (SN: 6/11/05, p. 379).

In most ape species, males are much larger than females and fight viciously to mate with fertile females, who advertise their availability with swollen red tissue. Females raise offspring on their own.

Lucy’s kind upended that arrangement, Lovejoy argued. Males grew only slightly larger than females and had small canines. Adults of both sexes favored long-term relationships as a matter of survival, he theorized. Males supplied food to regular partners with whom they had children, allowing females to spend more time raising their own children.

Monogamy worked, in Lovejoy’s view, because female anatomy evolved to mask obvious signs of ovulation that signal sexual readiness to males, instead developing features such as permanently enlarged breasts. Hit-and-run unions stood a good chance of yielding no offspring and thus became unappealing to both sexes.

Lovejoy’s evidence for minimal size differences between A. afarensis sexes has been sharply criticized. Critics charge that he’s underestimated the size disparities.

Detractors add that upright males with diminutive canines could have found plenty of ways to pummel one another in mating battles, even if they had to resort to fisticuffs.

With Ardi in tow, Lovejoy has now elaborated on his argument. A transition to monogamous relationships, expanded child care by mothers and hidden female ovulation first occurred before Lucy, in Ardipithecus, he proposes. Ardi’s kind displays even smaller sex differences in canine size than Lucy’s species. “Australopithecus represents a more intense version of what was already evolving in Ardipithecus,” Lovejoy says.

Cooperation among males later expanded in A. afarensis, he posits. Male bands scoured forests and savannas for food and worked together to avoid and defend against predators. [...]

To portray early hominids as a peaceful, monogamous crowd “is phenomenally speculative,” Plavcan says. Although large-bodied primate males with fanglike canines usually fight over mates, minimal sex differences can result in any of a variety of mating arrangements, he contends.

What’s more, Ardipithecus ramidus fossils do display size differences between the sexes sufficient to assume that males mated with several females, as in many other primates with size disparities, McGrew remarks.

“Lovejoy’s social hypothesis is an interesting just-so story,” Richmond asserts. “He’s winning the competition for the title of the Rudyard Kipling of paleoanthropology.”

Sublime.

Posted by Orrin Judd at January 10, 2010 9:08 AM